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• Hydraulic failure, but not carbon starvation, occurred towards mortality in all species under both drought treatments. • Rapid xylem repair after drought was not observed. • The recovery of photosynthesis was decoupled from water potential recovery. The impact of drought stress on dominant tree species of subtropical China, and the capacity of these species to recover from drought, is relatively unknown. Three ecologically important tree species (Syzygium rehderianum , Castanopsis chinensis and Schima superba), with contrasting drought sensitivities, were grown in pots under well-watered conditions in the glasshouse before being subjected to two drought treatments (i.e. higher intensity and shorter-duration fast drought(FD);lower intensity and longer-duration slow drought(SD)) towards mortality, and then re-watered to assess the rate of physiological recovery. Dry mass production and physiological traits related to water and carbon relations were measured over the experimental period. FD led to faster declines in hydraulic and photosynthetic function than SD in all species, while hydraulic failure occurred towards mortality in all species under both drought treatments. Although NSC responses varied among drought treatments and species, carbon starvation was not observed. S. rehderianum exhibited more rapid declines in leaf water potential and gas exchange traits, and shorter time-to-mortality, followed by C. chinensis and S. superba. Following re-watering, all three species showed rapid recovery of leaf water potential, while rapid recovery in stem hydraulic conductivity was not evident in any species. Furthermore, C. chinensis exhibited full rapid recovery of photosynthesis, but photosynthetic recovery in S. rehderianum and S. superba was slower than recovery of water potential, reflecting differential stomatal and biochemical limitations. The response of the three species to drought was strongly correlated with xylem embolism resistance, but recovery following drought was complex and partially associated with stomatal and biochemical traits. Under future longer and severe droughts, these species may diverge in drought responses and recovery, perhaps driving shifts in forest community structure in subtropical China. [ABSTRACT FROM AUTHOR]

Abstract The impacts of climate change on green water drought and associated economic activity can be simulated with future climate projections, hydrologic models that predict drought indices based on reliable soil moisture, and historic relationships between drought indices and agricultural sector impacts. This study compares the potential impacts of climate change on future agricultural drought and economic conditions in a rural and an urban congressional district in Northern Virginia (VA). The Variable Infiltration Capacity (VIC) model is applied to estimate a soil moisture index (SSI), which is then employed with historic and future climate data to generate SSI predictions. Economic impacts of future SSI changes are inferred from linear regression analysis of the historic relationship between annual mean SSI values and agricultural production values for a seven-year period (2010–2016). The two districts face similar future temperature and precipitation changes due to geographic proximity, but soil moisture, agricultural production and economy-wide responses to climate change differ considerably due to differences in land use and economic structure. In the more rural district, the mean value of drought occurrence increases 38%, while in the more urban district the increase is only 15%. Similarly, economy-wide agricultural sector value added decreases between 17% and 22% in the rural district and between 1 and 5% in the urban district. More studies are required to understand the impacts of adaption on agricultural and other economic sectors both rural and urban regions. More research should be carried out with an application of blue water droughts that have significant impacts to explain the economic impact of droughts. Graphical abstract Unlabelled Image Highlights • Impacts of climate change using coupled soil moisture and economic model. • Future drought occurrence increased over the study region. • Impacts of agriculture and economy differ due to land use and economic structure. • Agricultural sector value decreased 17–22% in rural and 1–5% in urban areas. [ABSTRACT FROM AUTHOR]

Highlights • The amendment with a K-rich compost under drought modulated pepper fruit quality. • Plants grown with carrot compost had low carotenoids and high phenols in fruits. • Carrot compost treatment increased fruit concentrations of minerals, mainly K. • Positive relationships between fruit K, proline and phenolic compounds were found. Abstract Water availability is the most critical factor to growth and development of plants, which limits the productive potential of plants. Plants adapt to water deficits by physiological alterations, biochemical changes and osmotic adjustments. The aim of this study was to investigate the effect of soil amendment of a K-rich carrot compost on pepper (Capsicum annuum L. cv. Paco) physiology and fruit quality under drought. Furthermore, an attempted to determine the influence of these combined factors on yield and quality pepper fruits. Carrot compost (ZC) was obtained by aerobic composting from carrot wastes from packing plants and not presented phytotoxic substances that prevented germination and grown of pepper seedlings. When the vegetative stage corresponding to start of flowering was reached, half of the plants were subjected to drought conditions (moderate water stress). Results showed that the concentration of minerals, free proline, total phenols and main carotenoids (β-carotene and lycopene) in pepper fruits were significantly modified by water level and/or substrate type. Under drought, plants grown in a mixture of 35% ZC and 65% soil (ZC35) increased concentrations of minerals (mainly K) and phenols but decreased β-carotene and lycopene levels. Moreover, significant relationships between K content, phenolic compounds and free proline were highlighted. Overall, data suggest that the use of a K-rich carrot compost for growing pepper under drought could selectively modify plant metabolic activities that are involved in the accumulation of carotenoids and phenolic compounds and thus, in fruit quality. [ABSTRACT FROM AUTHOR]

Highlights • The modulation of elevated CO 2 on stomatal response to progressive drought was studied in tomato plants. • Elevated CO 2 retarded the response of photosynthesis and stomatal conductance to soil water deficits. • The responsiveness of stomatal conductance to ABA was unaffected by CO 2 environment. • Elevated CO 2 enhanced both water use efficiency and nitrogen use efficiency in tomato plants. Abstract The objective of this study was to investigate the response of leaf gas exchange of tomato plant to progressive drought stress under ambient (a [CO 2 ], 400 ppm) and elevated (e [CO 2 ], 800 ppm) atmospheric CO 2 concentration. The fraction of transpirable soil water (FTSW) was used to evaluate soil water status in the pots. The results showed that stomatal conductance (g s) and transpiration rate (T r) were significantly lower while the net photosynthetic rate (A n) was significantly higher in plants grown under e [CO 2 ] than those under a [CO 2 ] at onset of drought stress. Along with soil drying, the FTSW thresholds at which g s and A n started to decrease were significantly lower in plants grown under e [CO 2 ] as compared to plants grown under a [CO 2 ]. The intrinsic water use efficiency and instantaneous water use efficiency of plants grown under e [CO 2 ] was significantly higher than those under a [CO 2 ]. Under e [CO 2 ], the drought-stressed plants had greater leaf area, dry matter and water use efficiency than those grown under a [CO 2 ]. e [CO 2 ] notably enhanced shoot C concentration while decreased shoot N concentration hereby increased the C:N ratio. With the decrease of FTSW, the concentration of abscisic acid in leaf ([ABA] leaf) and xylem sap ([ABA] xylem) increased exponentially. When FTSW > 0.2, under both CO 2 environments, g s decreased linearly with increasing [ABA] leaf and [ABA] xylem ; and similar slopes but different intercepts were noticed for the regression lines, indicating that the responsiveness of g s to ABA was unaffected by CO 2. In conclusion, CO 2 elevation retarded the response of leaf gas exchange to progressive soil drying in tomato plants. This result provides novel knowledge for more precise prediction of plant response to drought stress in a future CO 2 -enriched environment. [ABSTRACT FROM AUTHOR]

Highlights • A new drought index which integrated multi-sensor remote sensing data was developed. • The new drought index performances better than most existing integrated drought indices and single drought indices. • The new drought index does not require site information and local expert knowledge for good performance. Abstract Drought is one of the most expensive but least understood natural disasters. Remote sensing based integrated drought indices have the potential to describe drought conditions comprehensively, and multi-criteria combination analysis is increasingly used to support drought assessment. However, conventional multi-criteria combination methods and most existing integrated drought indices fail to adequately represent spatial variability. An index that can be widely used for drought monitoring across all climate regions would be of great value for ecosystem management. To this end, we proposed a framework for generating a new integrated drought index applicable across diverse climate regions. In this new framework, a local ordered weighted averaging (OWA) model was used to combine the Temperature Condition Index (TCI) from the Moderate-resolution Imaging Spectroradiometer (MODIS), the Vegetation Condition Index (VCI) developed using the Vegetation Index based on Universal Pattern Decomposition method (VIUPD), the Soil Moisture Condition Index (SMCI) derived from the Advanced Microwave Scanning Radiometer–Earth Observation System (AMSR-E), and the Precipitation Condition Index (PCI) derived from the Tropical Rainfall Measuring Mission (TRMM). This new index, which we call the "Geographically Independent Integrated Drought Index (GIIDI)," was validated in diverse climate divisions across the continental United States. Results showed that GIIDI was better correlated with in-situ PDSI, Z-index, SPI-1, SPI-3 and SPEI-6 (overall r-value = 0.701, 0.794, 0.811, 0.733, 0.628; RMSE = 1.979, 0.810, 0.729, 1.049 and 1.071, respectively) when compared to the Microwave Integrated Drought Index (MIDI), Optimized Meteorological Drought Index (OMDI), Scaled Drought Condition Index (SDCI), PCI, TCI, SMCI, and VCI. GIIDI also performed well in most climate divisions for both short-term and long-term drought monitoring. Because of the superior performance of GIIDI across diverse temporal and spatial scales, GIIDI has considerable potential for improving our ability to monitor drought across a range of biomes and climates. [ABSTRACT FROM AUTHOR]

Highlights • Land use and plant traits are important determinants of grassland drought responses. • The key drivers of grassland decline and recovery differed. • Grasslands response to land use variables differed between drought and wet phases. Abstract Climate change is expected to increase the frequency and intensity of drought globally with potentially significant consequences for grasslands. We examined grassland responses to a long-term drought on the Darling Downs, eastern Australia, using the Enhanced Vegetation Index (EVI), a remotely sensed measure of primary productivity. This extreme drought period had rainfall deficits comparable to the hottest and driest projected climate change scenarios for 2030 and was followed by extreme rainfall. This juxtaposition allowed investigation of grassland dynamics (decline and recovery) under extreme climatic variability. Our aim was to determine whether factors associated with grassland decline during extreme drought are the same as those that drive recovery post drought. There is limited knowledge about whether the determinants of grassland decline and recovery are consistent, but this information is important for understanding how best to reduce grassland decline, without inhibiting recovery. We calculated EVI (Enhanced Vegetation Index) trends at 2549 grassland sites situated in an agricultural landscape and used boosted regression trees to model these against multiple hydro-climatic and land use factors. As anticipated, hydro-climatic variables were key drivers of EVI trends in both the drought and wet phases, with higher soil moisture corresponding to less decline in the drought phase and enhanced recovery in the wet phase; however, land use and plant trait variables were also important predictors of EVI trends. Higher proportions of dryland agriculture in the local landscape, high C3:C4 ratios and lower proportions of woody vegetation in the local landscape were associated with negative EVI trends (i.e. greater decline) during drought, but had inverse or negligible effects during the post drought recovery phase. Our results suggest that mitigating decline and fostering grassland recovery following drought requires considering multiple hydro-climatic, land use and plant trait drivers and how their importance changes under drought and wet phases. [ABSTRACT FROM AUTHOR]

Highlights • Exogenous auxin-type compounds partially restored the growth of PEG-treated pea. • Auxin analogues TA-12 and TA-14 decreased the PEG-induced oxidative stress. • TA-12 and TA-14 modulated the free proline content under drought stress. Abstract Drought is among the abiotic stresses, which considerably decrease the agricultural production worldwide. The effects of exogenous auxin-type compounds 1-[2-chloroethoxycarbonyl-methyl]-4-naphthalenesulfonic acid calcium salt (TA-12) and 1-[2-dimethylaminoethoxicarbonylmethyl]naphthalene chlormethylate (TA-14) on drought stress responses induced by polyethylene glycol-6000 (PEG) in garden pea (Pisum sativum L.) plants were investigated. Preliminary application of TA compounds partially restored the normal growth of PEG-treated plants, led to less accumulation of proline, phenolic compounds and low-molecular thiols and did not provoke malondialdehyde buildup. The pea plants pretreated with auxin-type compounds displayed reduction in hydrogen peroxide content and consequently lower oxidative stress levels. This was confirmed by a decrease of the activity of the antioxidant enzymes superoxide dismutase, catalase, and guaiacol peroxidase. Taken together these results showed that the preliminary application of TA-12 and TA-14 reduced the negative effects of drought stress in pea plants. [ABSTRACT FROM AUTHOR]

Abstract Drought is a common environmental factor that limits plant growth, development and productivity. To understand the effect of drought on the perennial grass Bothriochloa ischaemum , we applied high-throughput Illumina sequencing technology and analyzed the transcriptional expression profile of Bothriochloa ischaemum leaves and roots under drought and normal growth conditions. Compared to the controls, drought-treated samples had 7989 differentially expressed genes in leaves and 15,675 differentially expressed genes in roots. Of these, 4489 and 5010 genes were up-regulated genes in leaves and roots, respectively. Of the 2012 differentially expressed genes that were shared between leaves and roots, 1068 were up-regulated. We identified common and distinct biological processes and metabolic pathways involved in drought stress between the two tissues. Most notably, there was a dramatic up-regulation of genes involved in plant hormone signal transduction especially ABA signal transduction components and flavonoid biosynthesis enzymes or regulation factors in drought stress treated leaves. Therefore, these two cellular processes likely confer resistance to drought stress in Bothriochloa ischaemum. Overall, our findings provided new insights into a mechanism involving the synergistic interaction between ABA signaling and secondary metabolism during the drought adaptation of Bothriochloa ischaemum. Highlights • We analyzed the effect of drought on B. ischaemum by transcriptome sequencing. • ABA signal transduction may confer resistance to drought stress in B. ischaemum. • Flavonoid biosynthesis likely confers resistance to drought stress in B. ischaemum. [ABSTRACT FROM AUTHOR]

Highlights • Both drought and salt stresses affect molecular, biochemical and physiological processes, which leads to decreased photosynthesis, plant growth, economic yield and fiber quality. • Genetic variation in abiotic stress tolerance exists within Gossypium hirsutum , and G. barbadense carries some level of tolerance to abioitc stresses. • Progress in screening methodology, resistance germplasm sources, inheritance, biochemical and molecular aspects, and quantitative trait loci (QTL) for drought and salt stress tolerance in cotton are reviewed. • Numerous drought or salt responsive genes have been identified, some of which are used in transgenic approaches for enhancement of abiotic stress tolerance in cotton. Abstract Drought stress, caused by lack of precipitation or irrigation, is one of the most challenging problems in crop production in the US and worldwide. Drought alone affects 45% of the world's agricultural land, further, 19.5% of irrigated agricultural lands are considered saline. A combination of two or more abiotic stresses, such as drought and salinity results in more yield loss than a single stress. Drought along with salinization is expected to cause up to 50% of arable land loss worldwide. Development of drought and/or salt stress tolerant cultivars represents one of the most practical solutions. Genetic variation in abiotic stress tolerance exists within Upland cotton (Gossypium hirsutum L.); however, most if not all Upland cultivars have been developed under normal well-watered and non-saline conditions. Pima, Sea-Island or Egyptian cotton (G. barbadense L.), carries some level of tolerance to abioitc stresses due to their origin near sea-coasts, and this tolerance can be transferred to Upland cotton by interspecific introgression. Although drought and salt stress tolerances are presumed to be interconnected, the genetic basis is not fully understood due to complexity of the stress resistance and difficulties in phenotyping. The objective of this review was to summarize the progress in screening methodology, resistance germplasm sources, inheritance, biochemical and molecular aspects, transgenic approaches, and quantitative trait loci (QTL) for drought and salt stress tolerance in cotton. In the last 10–15 years, significant progress has been made in understanding the genetic basis of drought and salt tolerance through QTL mapping using molecular markers on biparental and multi-parental populations and natural populations. Numerous drought or salt responsive genes have been identified, some of which include those commonly associated with drought or salt tolerance in other plants and are used in transgenic approaches for enhancement of abiotic stress tolerance. However, none of these genes have been utilized in commercial cotton breeding programs, and no abiotic stress tolerance QTL has been used in cotton breeding through marker-assisted selection (MAS). More and larger permanent intra-specific and interspecific mapping populations using diverse and multiple parents should be developed. These populations are necessary for repeated phenotyping for abiotic stress tolerance and for high resolution mapping of QTL using genome-wide SNP markers and for MAS to transfer tolerance genes to high-yielding cultivars. Further, quick, reliable and high throughput screening methods applicable for large scale populations need to be developed to improve the reliability and scale of phenotyping of the cotton germplasm in these populations for drought and salt stress tolerance. [ABSTRACT FROM AUTHOR]

Abstract This research was conducted to address the influence of foliage-applied sodium nitroprusside (SNP; 0, 50, 100 and 150 μM) on resistance against reduced irrigation by 80, 60 and 40% Field Capacity (FC), in two drought tolerant thyme (Thymus serpyllum Serpolet) and drought susceptible thyme (T. Vulgaris L.). Non-SNP treated resistant specie showed 55.17% higher plant growth rate than drought susceptible thyme under severe water deficit (40% FC). However, SNP treatment caused drought susceptible specie to show higher growth rate compared with those of resistant one under non- water stressed conditions (80% FC). Intensified drought, while significantly enhancing malondialdehyde (MDA), H 2 O 2 and electrolyte leakage of both specie, caused marked reduction in chlorophyll content, ratio of variable to maximum fluorescence (Fv/Fm) and relative water content. The essential oil yield of both specie increased with the decrease in irrigation from 80 to 60% FC, and decreased with the water deficit increase to 40% FC. Spraying Thymus specie with all three levels of SNP further increased the essential oil yield and improved physiological attributes of both specie, being more pronounced in drought resistant one. The compensatory effect of SNP in mitigating the negative impact of reduced irrigation was due to increase of proline accumulation and reduction of some antioxidant activities which increased drought tolerance of Thymus. [ABSTRACT FROM AUTHOR]

Highlights • Soil water deficit treatment significantly increase the number of first-flush summertime flowers in Meiwa kumquat. • Transpiration occurred from the stem surface but the rate was approximately one-eighth of that from the leaf under non-stressed conditions. • Despite the rapid decrease in the transpiration of the leaves, that of the stem remained unchanged during soil water deficit treatment. • Increase in the monosaccharides due to the soil water deficit treatment also occurred even in the xylem of scaffold branches. Abstract Drought induce various physiological changes such as flowering advancement and carbohydrate accumulation in many plants. Soil water deficit (SWD) has been shown to significantly increase the number of first-flush summertime flowers in the ever-flowering Meiwa kumquat (Fortunella crassifolia Swingle). In this study, we examined how SWD affects transpiration and the accumulation of soluble sugars in various parts of the plant as a result of osmoregulation. Despite the rapid decrease in the transpiration of the leaves, that of the stem remained unchanged during SWD treatment at one-eighth of that from the leaves under non-stressed conditions. The SWD treatment increased the total soluble sugar content in all plant parts, except the leaves. Increase in the monosaccharides such as glucose and fructose being greater than for the disaccharide sucrose, in the stems of shoots more than 3 years of age as well as in the xylem of scaffold branches, is suggesting that these increased sugar levels were due to osmoregulation. The sucrose content decreased markedly during the 4 months after SWD treatment in the xylem of scaffold branches but was significantly higher in the fruit that were harvested from SWD-treated trees at 4 months after SWD treatment. These results suggest that the sugars that are accumulated in the xylem positively affect fruit growth after SWD treatment. [ABSTRACT FROM AUTHOR]

Abstract Echinacea purpurea is an important industrial and ornamental plant that its quality and physiological parameters may be negatively affected by drought, however, negative effects of drought could be reversed by application of plant growth regulators such as salicylic acid (SA) and spermine (SPM). Therefore, this experiment was conducted to investigate the effects of irrigation regimes (irrigation after 20, 40 and 60% soil water depletion) and, SA and SPM treatments (no spray, 75 mg L−1 SA, 150 mg L−1 SA, 70 mg L−1 SPM, 75 mg L−1 SA + 70 mg L−1 SPM and 150 mg L−1 SA + 70 mg L−1 SPM) on the activities of antioxidant enzymes catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX) and superoxide dismutase (SOD), shoot dry mass (SDM), chlorophyll (Chl), carotenoid (Caro), proline (Pro), phenol, flavonoid and Malondialdehyde (MDA) in purple coneflower (Echinacea purpurea L.). Water deficit increased the activities of enzymes, and the contents of carotenoids, proline, MDA, phenol and flavonoid while it decreased chlorophyll content and shoot dry mass. Among tested enzymes, CAT showed the highest increase in response to water deficit. SA and SPM application increased antioxidant enzymes activities, shoot dry mass and the contents of chlorophyll, carotenoid, proline and flavonoid (only by SA application), but decreased phenol and MDA contents. SOD was the most responsive enzyme to SA and SPM. However, the magnitude of SA and SPM effects was dependent on the level of soil available water. The positive effects of SA were greater than those of SPM. The superiority of SA over SPM was more pronounced at higher level of water deficit. The effects of SA application were greater at 150 than at 75 mg L−1. The highest plant biomass was produced under combined application of SA and SPM. These results indicated that SA and SPM improve purple coneflower growth under water deficit by stimulating antioxidant defense system, alleviating lipid peroxidation and increasing osmotic adjustment. The results also suggest that growers can use SA and SPM to increase productivity of purple coneflower under drought stress. [ABSTRACT FROM AUTHOR]

Highlights • Our data showed that autotetraploids showed higher tolerance to drought stress than diploids. • Autopolyploid does not seem to undergo major changes of gene expression over long periods (2.84%) and under drought stress. • Genome duplication resulted in more differentially expressed drought-related genes in autopolyploid than in diploid. • Genome duplication also resulted in gain or loss of drought-related genes. Abstract The evolutionary mechanism where autopolyploid tolerate abiotic stresses better than its diploid ancestor is poorly known. Large-scale gene-expression changes were not observed in synthetic autopolyploids compared to their respective diploids. However, natural autopolyploids with longer evolutionary periods might have experienced major changes that resulted in greater adaptation of autopolyploids, which might contribute to gene expression in natural autopolyploid differently from that in synthetic autopolyploid, and explain why genome doubling can help plants develop a stronger ability to adapt to various environmental stresses. However, information on this is still lacking. Here, diploid and autotetraploid sea barley tolerance to drought stress were analyzed. Our data showed that autotetraploids showed higher tolerance to drought stress than diploids. The results of GO enrichment and KEGG pathway enrichment showed that diploid and tetraploid would alter their physiological and biochemical process, even morphology to respond to drought stress via different molecular mechanism. Genome duplication resulted in more differentially expressed drought-related genes and higher expression level of those genes in autopolyploid than in diploid, 186 drought-related genes with 97 genes up-regulated in comparison of DiH826Dr_vs_DiH826Ck, while 297 drought-related genes with 126 up-regulated in TetraH832Dr_vs_TetraH832Ck. Among these drought-related genes, 81 of them were specific significantly expressed in DiH826Dr_vs_DiH826Ck, 192 genes were specific significantly expressed in TetraH832Dr_vs_TetraH832Ck. Although our results indicated that the autopolyploid does not seem to undergo major changes of gene expression over long periods (2.84%) and under drought stress, more DEGs and more up-regulated DEGs between autotetraploid and diploid were observed than those in the CK. Furthermore, genome duplication also resulted in gain or loss of drought-related genes, which might offer potential for autopolyploid to survive better under drought environment. [ABSTRACT FROM AUTHOR]

Highlights • Gibberellin deficiency increases the partition of reserves to the root compared to the shoot. • Impaired GAs biosynthesis lead to pronounced alterations in the primary metabolism, mainly following water limitation. • Water deficit elevates the amino acid content, especially proline, in leaves and roots of gibberellin biosynthesis mutant. • The lack of gibberellin promotes maintenance of the water content and thereby enhancing tolerance to the water deficit. Abstract Gibberellins (GAs) have been shown to be involved in the tolerance of plants to a range of environmental stresses. However, the physiological and metabolic implications of altered levels of GAs in plants under drought stress remain largely unknown. To understand the contribution of GAs for the responses to water deficit conditions, physiological and metabolic parameters were evaluated in tomato deficient mutants in GAs biosynthesis, gib1 , gib2 , and gib3. Interestingly, the mutants maintained leaf water content over a longer time period and recovered photosynthesis faster than wild-type (WT) plants. Furthermore, gib1 and gib2 plants showed no apparent wilt even after reaching low leaf water potential (-1.3 MPa). Additionally, mutants plants partitioned more biomass to the roots than shoots compared to WT. The maintenance of leaf water content and consequent increased water use efficiency observed in the mutants can be explained by the osmotic adjustment of leaf and root cells, mainly due to amino acid accumulation. Collectively, our results suggest that plants with reduced GAs content are able to cope with water deprivation by increasing proline and other amino acid levels. This response, alongside partitioning of carbon to roots allows GAs-deficient plants to maintain the leaf turgor for a longer time and thereby promotes water deficit tolerance. [ABSTRACT FROM AUTHOR]

Highlights • Photosynthetic enzymes are regulated spatially and temporally by epigenetic mechanisms. • Light and drought stress disturb different types of photosynthesis. • miRNAs and their functions is different among plant species. Abstract Without photosynthesis, life on earth as we know it would be impossible. Advances in our understanding of how light harvesting and carbon fixation work have traditionally been driven by biochemical and molecular approaches with the goal of increasing crop yield. However, environmental challenges are putting the survival of many plants at risk due to photosynthetic inbalance. Epigenetic regulation has only recently been recognized as an important player in the response to changes in key environmental conditions such as light, temperature and drought, and while there has been scattered research on the topic, it has not yet been collated into a review. Here we focus on epigenetics' affect on photosynthesis-related carbon fixation pathways and identify important directions for future research. For instance, during the perception of light, epigenetic regulation mediates a complex and flexible series of events, including histone acetylation and DNA demethylation, to promote expression of several genes involved in carbon fixation, such as RuBisCO and PEPC in C 3 and C 4 plants, respectively. On the other hand, the crucial role of deacetylases of histones HD1 and HDA15 and the possible participation of miRNAs during light/dark signaling and light harvesting, respectively, reveal an unexplored connection between light signaling and epigenetic regulation during photosynthesis. In the present review, we highlight how euchromatin configuration helps in the acquisition of drought tolerance and efficient stomata conductance. Therefore, we suggest that several drought-sensitive crops could be improved with the use of miRNA to optimize photosynthetic stomata conductance and gas exchange. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Growth regulator affected the dry weight production. • Naphthaleneacetic acid and 6-benzylaminopurine induced higher shoot number as predict by response surface. • Carvacrol and thymol were influenced in media supplemented with growth regulator. • Higher carvacrol contents was found in the medium without growth regulator. Abstract The essential oil from Lippia gracilis Schauer (Verbenaceae) leaves are rich in thymol and carvacrol with antibactericidal and antinflammatory action. The aim of the present study was to evaluate the effect of growth regulators and their combinations on shoot proliferation, growth, and volatile fraction analysis of Lippia gracilis in vitro. In the first experiment, five different concentrations of 6-benzylaminopurine (BAP) were used: 0.0, 2.22, 3.33, 4.44, and 5.55 μM and three of naphthaleneacetic acid (NAA): 0.0, 2.68, and 5.36 μM, in a factorial design. In the second, the treatments consisted in combination of BAP + TDZ at concentration (μM): 0 + 0, 1.11 + 1.13, 1.33 + 0.91, 0.88 + 1.36, 0.43 + 1.81, and 1.78 + 0.46. At 30 days of culture in ½ Murashige and Skoog (MS) medium, the growth and volatile constituents were evaluated. Growth regulators significantly influenced in vitro growth of L. gracilis. Growth data for the first experiment were predicted from the three-dimensional (3D) response surface of the different variables analyzed. In the second experiment, the presence of growth regulators reduced shoots and root length in all combinations. The combinations among regulators (BAP and TDZ) stimulated the number of shoots per explant, but BAP and NAA induced higher shoot number. Variation in the number, content, and profile of volatile compounds were also observed under the influence of growth regulators. The major constituents ρ-cimene, γ-terpinene, thymol, carvacrol, and E- caryophyllene were identified, independent of the experimental conditions. However, the use of growth regulators significantly reduced carvacrol and thymol levels. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • New insights regarding the mechanisms and processes involved in S. dolomitica drought adaptation are provided. • Moderate drought decreased growth, leaf water potential and stomatal conductance, while increased deyhdrin gene expression. • Severe drought decreased net photosynthesis and transpiration rate. • Drought increased sesquiterpene production by modulating gene expression of key enzymes of terpenoid biosynthesis. • Moderate drought can ameliorate secondary metabolites production and water-management practices in S. dolomitica. Abstract Sage is an important medicinal and aromatic plant. While Salvia officinalis and S. miltiorrhiza have been widely studied, little information regarding S. dolomitica exists, although it has recently attracted attention due to its anti-plasmodial and anti-inflammatory properties. This study investigated the performance and metabolic profile of this species in response to two drought treatments (moderate or severe) relative to well-watered control plants. Changes in growth and ecophysiological traits, as well as in bioactive and volatile compounds and essential oil production were determined. Given that terpenoids are the most representative class of secondary metabolites, the gene expression of key enzymes of terpenoid biosynthesis was also investigated. Moderate drought stimulated a decline in leaf water potential, growth and stomatal conductance, as well as an increase in deyhdrin expression. Serious stress symptoms occurred only in severe drought-stressed plants, where a decline in net photosynthesis and transpiration and an increase in endogenous abscisic acid was observed. Both drought stress conditions led to modulate the expression of some genes involved in biogenic volatile organic compound and essential oil biosynthesis and metabolic profile. In particular, drought induced an increase in sesquiterpene production, a class of terpenoids that is important in the food, cosmetics, and pharmaceutical industries. Thus, controlled drought, in addition to water savings during cultivation, can be applied to improve the production of secondary metabolites in S. dolomitica. [ABSTRACT FROM AUTHOR]

Highlights • The anti-transpirant Vapor Gard has a beneficial, albeit temporary, effect in pea. • Reduced transpiration causes an early inhibition of symbiotic nitrogen fixation. • Regulation of nitrogen fixation is not associated with amino acid accumulation. Abstract Stomatal closure is one of the first plant responses under a water deficit situation. This leads to a decline in transpiration but also in the plant photosynthetic activity. Legume plants grown under symbiosis with rhizobium bacteria present an inhibition of nitrogen fixation that has been shown to occur even before this of photosynthesis. One of the hypotheses to explain this rapid inhibition is the accumulation of nitrogen (N) compounds in nodules due to reduced transpiration, which would provoke the N-feedback inhibition of nitrogenase activity. The current work analyzes the effects of changes in transpiration rates in the regulation of nitrogen fixation through the application of the anti-transpirant Vapor Gard (VG) to pea (Pisum sativum L.) plants subjected to a progressive water deficit. VG produced a rapid inhibition of nitrogen fixation upon application. This inhibition, however, did not coincide with the accumulation of either amino acids or soluble carbohydrates observed at later drought stages in nodules. Results show that the application of VG has a beneficial, albeit temporary, effect in both maintaining the plant water status and apparent nitrogenase activity of nodulated pea plants under water-deficit conditions. [ABSTRACT FROM AUTHOR]

Highlights • Drought and saline water caused permanent damages to olive leaf activity. • Water status recovery after a severe drought. • physiological performance of olive not fully recovered after re-watering. • Saline water irrigation reduced drought impact on olive tree growth. • Young leaves have the same photosynthetic capacity indecently of the stress. Abstract Effects of drought and salinity on water status, growth and physiological activity of olive can be temporary or permanent and may impact olive production sustainability, especially in southern Mediterranean areas. Tunisia has a Mediterranean climate with high temperatures and low summer rainfall. Thus water stress problems are likely to be more severe for cultivated olive trees. In addition, the reduction in the availability of good quality irrigation water will increase the use of saline water. Olive trees are able to tolerate low soil water availability and quality and develop physiological adaptations to cope with water and salt stress. However, these adaptation strategies are limited and permanent damages can be observed. The permanent effects caused to olive leaves due to drought, and the capacity of irrigation with saline water to avoid these impacts is not well known. The aim of this work was to compare olive leaves performance after a severe drought with, and without, irrigation and to assess recovering capacities after a rainy period. Moreover, irrigation water quality effects were also evaluated. The results showed that, photosynthetic rate was very low for rainfed plants, during drought, as compared to irrigated ones. After re-watering, rainfed trees photosynthetic rate was only 55% of that of trees irrigated with fresh water. Irrigation with saline water (EC = 7.5 dS m−1) reduced drought impact by increasing photosynthesis by 55% but remained lower than that of fresh water by 23%. Thus olive leaves were unable to recover their whole photosynthetic capacity after being exposed to severe water or salt stress. Furthermore, young leaves had the same photosynthetic capacity at the beginning. This indicated that olive leaves lost permanently half of their photosynthetic activity during to drought without irrigation. The use of saline water reduced this gap to 23% as compared to fresh water. [ABSTRACT FROM AUTHOR]

Highlights • Northeast China is the center of maize production in the country. • Assess varying impacts of drought across different maize growth stages in Northeast China. • Probability of extreme events in irrigation water shortage will increase in the future. • Irrigation infrastructure and efficient irrigation scheme and technologies are of great importance. Abstract Northeast Farming Region of China (NFR) produces about one-third of the national maize output. Shortage of crop irrigation water is one of the main threat to the stable level of maize production in the NFR. Previous studies on the sensitivity of maize production to drought are typically based on field experiments and treat the maize growing season as a whole, with rare attention to the varying impacts of drought across different maize growth stages. Given the importance of NFR on China's food security, it is crucial to optimize the irrigation schedule to mitigate the adverse effects of drought. In this study, we employ Agro-ecological Zone (AEZ) model to investigate how climate change affects irrigation water requirement (IWR) of maize during different growth stages and under different climate change scenarios. Results indicate that the NFR would experience a substantial increase in the probability of extremely shortage of crop irrigation water under future climate change. The ensemble simulation under future climate projections indicates more frequent demands for irrigation with substantially increased amount in the mid-season stage (G3) when maize is more sensitive to water deficit compared with other stages. These findings indicate that earlier planning of irrigation infrastructure and development of more efficient irrigation scheme and technologies is of great importance to secure maize production in the region. [ABSTRACT FROM AUTHOR]

Highlights • Models based on VCI/TCI explained 70% of wheat and barley yield level annual variability. • Validation tests at agricultural districts confirmed better fit of VCI/TCI-based crop models compared to SPI-based models. • Both families of indices (meteorological and satellite) fail to explain yield variability of maize, mostly rainfed in Spain. • VCI/TCI-based models performed better than SPI-based as in-season, real-time yield forecasting tools. Abstract In the context of global warming, as drought episodes become increasingly frequent, it is crucial to accurately measure the impacts of droughts on the overall performance of agrosystems. This study aims to compare the effectiveness of meteorological drought indices against satellite-based agronomical drought indices as crop yield explanatory factors in statistical models calibrated at a local scale. The analysis is conducted in Spain using a spatially detailed, 12-year (2003–2015) dataset on crop yields, including different types of cereals. Yields and drought indices were spatially aggregated at the agricultural district level. The Standardised Precipitation Index (SPI), computed at different temporal aggregation levels, and two satellite-based drought indices, the Vegetation Condition Index (VCI) and the Temperature Condition Index (TCI), were used to characterise the dynamics of drought severity conditions in the study area. Models resting on satellite-based indices showed higher performance in explaining yield levels as well as yield anomalies for all the crops evaluated. In particular, VCI/TCI models of winter wheat and barley were able to explain 70% and 40% of annual crop yield level and crop yield anomaly variability, respectively. We also observed gains in explanatory power when models for climate zones (instead of models at the national scale) were considered. All the results were cross-validated on subsamples of the whole dataset and on models fitted to individual agricultural districts and their predictive accuracy was assessed with a real-time forecasting exercise. Results from this study highlight the potential for including satellite-based drought indices in agricultural decision support systems (e.g. agricultural drought early warning systems, crop yield forecasting models or water resource management tools) complementing meteorological drought indices derived from precipitation grids. [ABSTRACT FROM AUTHOR]

Highlights • Water deficits in Michigan asparagus production have increased linearly since 1997. • Irrigation reduced losses due to drought stress for one of two cultivars. • Cultivar differences in drought tolerance were likely due to differences in rooting depth. Abstract Increasing temperatures and rainfall variability in the Midwestern U.S. have spurred interest in strategies to reduce risks of heat and drought stress in traditionally rainfed crops including asparagus. A long-term field experiment was conducted on sandy soils in Western Michigan from 2010-17 to evaluate the effects of three levels of irrigation (none, overhead or sub-surface drip) and two asparagus cultivars (Guelph Millennium [GM] and Jersey Supreme [JS]) for reducing these risks. Overhead irrigation during the fern growth period resulted in cumulative yield improvements of 10% for GM during the 2012-17 growing seasons, with the largest yield benefits (21%) occurring in 2012, following hot, dry conditions the previous summer. In contrast, cumulative yields of JS were unaffected by irrigation, and yield reductions of 13% due to irrigation were observed in 2017, following wet conditions the previous late summer and fall. Estimates of cultivar water-use by depth suggest that JS was better able to tolerate drought due to a deeper root system compared to GM. However, our results suggest that JS may also be more sensitive than GM to excessive soil moisture during fall senescence. Yield response did not vary with delivery system, but sub-surface drip used less water than overhead irrigation. These results demonstrate the important role of both genetics and management practices in mitigating drought risk. [ABSTRACT FROM AUTHOR]

Highlights • 2/3 of full irrigation coupled with 0.3% soil salt reduced tomato yield by 20.3%–32.0%, while fruit quality parameters increased by 4.9%–43.4%. • Soil salt content at which yield decreased by 50% was 4‰ in the non-linear reduction model. • Fruit quality parameters were more affected by salt stress than water stress. • Fruit growth process was simulated using EPIC growth model under deficit irrigation and salt stress conditions. Abstract Owing to the severe shortages of fresh water in arid and semi-arid areas, growers are forced to apply deficit irrigation with fresh or saline water. To quantify the impacts of water deficit and salt stress individually and the interaction on tomato yield and quality, three pot experiments were conducted from spring 2016 to autumn 2017. The EPIC growth model was also used to simulate fruit growth process. Three irrigation treatments used were full irrigation, 2/3 and 1/2 of the full irrigation. Salt stress varied with the season: 0, 3‰, 6‰, 9‰ for 2016 season, 0, 3‰ for 2016–2017 season and 0, 2‰, 3‰, 4‰ for 2017 season. Decreases in single fruit weights were associated with increasing soil salt content. However, fruit quality parameters including CI (color index), TSS (total soluble solids) and TSSC (total soluble sugar content) improved significantly with increasing salt content of soil. In the absence of salt stress, the application of 2/3 of full irrigation showed a 18.9% and 1.0% increase of yield per plant, respectively in 2016 and 2017 seasons with comparison to full irrigation, mainly owing to the increase of fruits number per plant. Fruit quality also improved with increasing Fn (fruit firmness), CI, TSS and TSSC by 7.9%, 43.8%, 9.8% and 3.8% in 2016 season, and by 4.7%, 0.7%, 20.9% and 34.2% in 2017 season, respectively. Fruit quality parameters were more affected by salt stress than drought, the interactive impact of water and salt on fruit quality parameters was not significant. At mild water stress (2/3 of full irrigation) with moderate salt stress (salt content of 3‰), although yield showed a decline of 20.3%–32.0%, fruit quality parameters of Fn, CI, TSS and TSSC increased by 4.9%–43.4% through 2016 and 2017 seasons. Two of van Genuchten and Hoffman models (i.e. non-linear and exponential reduction model) were used to evaluate the relations of relative yield and soil salt content with acceptable accuracy, R2 of 0.989 and 0.971, respectively. Soil salt content at which yield decreased by 50% is 4.0‰ and 4.7‰, respectively in the non-linear reduction model and the exponential reduction model. The EPIC growth model simulated fruit growth process with acceptable accuracy for no stress, water stress and salt stress, with R2 of 0.863, 0.839 and 0.895, respectively. The two yield reduction models and the relationship between fruit quality parameters and soil salt content showed that there are tradeoffs between tomato yield and fruit quality in saline soils. [ABSTRACT FROM AUTHOR]

Highlights • Crop sensitivity to a water deficit is defined as the yield loss under this deficit intensity. • S-shaped soybean drought loss sensitivity curves are built for four growth stages. • Soybean seed formation sensitivity to water deficit varies with the deficit degree. • Soybean tolerance to drought during the seedling stage is relatively weak. • Severe drought at soybean flowering and pod-enlargement stage significantly reduces yield. Abstract Crop drought loss sensitivity assessment is fundamental for managing agricultural drought risk. Potted soybean water deficit experiments with different irrigation treatments during two seasons (2015 and 2016) were conducted in China's Huaibei Plain. S-shaped soybean drought loss sensitivity curves at four growth periods were established, and the sensitivity of seed formation to water deficit during different stages was quantitatively compared. The results indicated that the negative effects of water deficit during the flowering-podding and seed filling stages on yield formation were greater than those during the branching and seedling stages. Similarly, aboveground biomass and 1000 seed weight both reached the minimum when soybeans encountered a severe water deficit during the seed filling stage. According to the parameters of the sensitivity curve, the seed yield loss was the greatest when soybeans experienced severe drought stress during the flowering-podding stage. In addition, soybean tolerance to drought during the seedling stage was relatively weak. Moreover, the sensitivity at each growth period varied with water deficit intensity. If there was a mild water defict, soybean yield formation was more sensitive to the deficit when it occurred during the seedling stage. However, if the deficit was relatively serious, yield formation became more sensitive when it happened during the flowering-podding stage. Therefore, it is crucial to strictly control the water deficit intensity during the seedling stage and ensure an adequate water supply during the reproductive growth period, especially during the flowering and pod-enlargement stage, for guaranteeing a high soybean yield. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Trees near springs have higher absolute and relative growth than those away from springs. • Trees away from springs are more sensitive to climate change. • Differences in tree response are persistent and may facilitate survival under warming climate. Abstract Tree rings have been widely used to reconstruct environmental history, especially water availability, because historical records of streamflow are often limited. In the semiarid southwestern USA, springs provide critical water resources and support biodiversity hotspots, but spring flows are poorly documented and spring effects on tree-ring growth are not well studied. Our project was designed to measure the effect of spring adjacency on ponderosa pine tree growth and drought response. We sampled trees adjacent to springs ("near") and farther away ("away") that were similar in latitude, slope, soil characteristics, height and stem diameter, so we inferred that differences in ring width were due to the springś influences. We gathered cores from a total of 50 ponderosa pine trees at ten different springs around Flagstaff, Arizona. We crossdated and measured the tree rings and developed chronologies of near and away trees. We compared absolute growth of trees in each category using basal area increment (BAI; mm2/year), which ranged from 806 to 2511 mm2 tree −1 year−1 near springs and between 503 and 2125 mm2 tree −1 year−1 away from springs. Near trees had consistently higher BAI growth over the past 66 years, the common period of analysis, although the difference was not statistically significant. Mean tree-ring sensitivity from the chronology near springs was 0.323, while the chronology away from springs was significantly higher, 0.366. Drought sensitivity index was significantly higher for away trees, indicating that years of severe drought had a greater negative impact for away than for near trees. Drought recovery index, however, showed inconsistent results. The findings indicate that ponderosa pine growth is responsive to spring settings, even in severe drought. Given that small springs are abundant in semiarid regions, they may provide valuable ecological buffers for warming climate. Further investigation to quantify springs perenniality and variability is needed. [ABSTRACT FROM AUTHOR]

Highlights • We focused on tree-ring width (RWI) and potential evapotranspiration index (SPEI). • The relationship between RWI and SPEI was stronger under drier conditions. • SPEI of November and June were the most important predictors explaining RWI. • Beech tree growth was controlled by soil water supply and atmospheric evaporative demand. Abstract Due to the recent spread of forest die-off worldwide, concerns arise about the relative influence of specific climate parameters on tree growth decline in semi-arid environments, such as the Mediterranean mountain forests. As temperatures increase, drought may reduce tree productivity and survival across these forest ecosystems. Drought-induced tree growth decline can be interpreted as an early-warning signal of forest vulnerability. Here, we modeled the relationship between tree-ring width index (RWI) of beech populations in mountain forests of south-central Italy and the standardized precipitation evapotranspiration index (SPEI) derived from local weather stations. The aim of the research was to propose a procedure to determine the tipping point of drought severity triggering tree decline in beech forests. We focused on the cumulative water balance over the previous 1 month, which was particularly appropriate in relationship with the soil water conditions of these Mediterranean mountains. Under drier conditions, the correlation between RWI and SPEI was stronger, soil water supply (early fall of current year) and atmospheric evaporative demand (late spring of current year) being the dominant factors limiting tree growth of southern beech populations. [ABSTRACT FROM AUTHOR]

Highlights • There has been a strong climate transition change from warm-dry to warm-wet. • Drought still was limiting factor for radial growth of two dominant conifer trees. • Siberian larch had divergent response with first increase and then decrease trend. • Schrenk spruce had stable responses showing continuously decreasing growth trend. • Water management should be adjusted according to trees response characteristics. Abstract As global climate warming intensified in the latter half of the 20th century, the radial growth of trees exhibited unstable climate responses and growth trends, thereby reducing the accuracy of growth-climate ecological relationship and the scientificity of forest management based on tree rings. We assessed the temporal stability of radial growth responses and determined the growth patterns of two dominant co-occurring conifer tree species, Siberian larch (Larix sibirica) and Schrenk spruce (Picea schrenkiana), in the Tianshan Mountains of northwest China under a climate that shifted from warm-dry to warm-wet. The primary conclusions were as follows: (1) drought in the growing season was the main limiting factor of radial growth of the two tree species in recent decades through the analysis of the dynamic relationships between tree radial growth and climate factors; (2) Siberian larch had divergent responses to mean temperature in summer of the previous year, while Schrenk spruce had relatively stable responses to the mean temperature, total precipitation and monthly standardized precipitation-evapotranspiration index (SPEI) in spring of the current year by comparing the response variations before and after the abrupt increases in temperature and the moving correlation function; and (3) Siberian larch showed first increasing and then decreasing trends, while Schrenk spruce showed continuously decreasing trends based on calculating the basal area increment (BAI). The study results confirmed that forests in arid and semiarid environments would be subjected to more serious drought impacts, resulting in radial growth decline, tree mortality and community degradation with climate warming in the future. Therefore, it is important to adopt effective management measures for different species according to their response characteristics to climate change. [ABSTRACT FROM AUTHOR]

Highlights • Drought resilience of two tropical tree species was studied. • Species-specific and temporal variability in drought tolerance were observed. • LMEM revealed that growth rates before and after the drought events had a dominant role in drought responses. Abstract The frequency and intensity of drought events have increased during the recent decades, particularly in the tropics. Yet, the growth and physiological responses of many tropical tree species to drought are still inadequately understood. We studied the drought resilience of two functionally different canopy tree species (Chukrasia tabularis and Toona ciliata) from a moist tropical forest in Bangladesh during two extreme drought events (1984 and 1999). We quantified four resilience components (resistance, recovery, resilience and relative resilience) of both species to infer drought tolerance of selected trees. Tree radial growth dropped by 44–56% in the drought years, varying with species and drought events. Two species showed no differences in their drought resistance during any of the drought events. However, C. tabularis showed higher recovery and resilience than T. ciliata after the 1999 drought event. T. ciliata showed higher resilience after the 1984 drought event. Linear mixed effect model (LMEM) revealed that growth rates in the two years before and after the drought events had a dominant role in drought responses over tree age, height, diameter, basal area increment and crown exposure, although crown exposure had significant influence on the resistance and the resilience of light demanding T. ciliata. We conclude that diffuse porous and intermediate shade tolerant C. tabularis is more drought tolerant than the ring-porous and light demanding T. ciliata. Since both study species are widely used as plantation species throughout the tropics, our results have important implications for forest managers to take decision on species suitability for plantation programs and to adopt forest management to future climate change conditions. [ABSTRACT FROM AUTHOR]

Highlights • Sirex noctilio outbreaks are synchronized at a regional scale. • Occurrence of S. noctilio outbreaks are triggered by an abrupt increase in drought. • Tree mortality decrease due to negative density-dependence in S. noctilio populations. • The damage caused by the outbreaks is determined by stand management variables. Abstract Insect outbreaks are among the most important biotic disturbances in forest ecosystems and can exert immense economic and ecological impacts. Understanding the spatio-temporal patterns of eruptive insects can provide insights into the mechanisms driving their dynamics and help predict future responses under climate change. The aims of this study were to analyze the spatio-temporal patterns of outbreaks of the woodwasp Sirex noctilio –a major invasive pest of pines– in an invaded region of South America, to assess the relative importance of density-dependent and density-independent mechanisms on population dynamics, and to identify the primary factors that influence the magnitude of outbreaks. We used tree ring and insect sampling data of more than 1000 trees to reconstruct S. noctilio outbreaks in 29 pine stands across Patagonia-Argentina over a 16-year period. We found marked spatial synchrony in S. noctilio outbreaks at a regional scale. Rates of tree mortality from S. noctilio were influenced by both density-dependent and density-independent factors. The occurrence of S. noctilio outbreaks are triggered by an abrupt increase in drought, which likely increases the availability of susceptible host trees. The damage caused by the outbreaks is determined by stand level variables, closely related with tree stress. Rates of tree mortality decreased over time due to negative density-dependence in S. noctilio populations, likely due to the loss of suitable resources over time. Depicting mechanisms of large-scale tree mortality in ecosystems provides insights to the drivers of forest outbreaks and other factors such as responses to a changing climate. [ABSTRACT FROM AUTHOR]

Highlights • Forest fragmentation is widespread in Mongolia's forest-steppe ecotone. • It is known to increase the drought sensitivity of tree growth in these forests. • Here the hypothesis was tested whether fragmentation degrades the organic carbon pool. • Organic layer carbon stock density increased with stand size. • Total ecosystem carbon stock density did not vary with stand size and isolation. Abstract The hypothesis was tested that the size and the degree of isolation of Larix sibirica forests in the forest-steppe ecotone of Mongolia affects aboveground and belowground carbon pool densities. The research question was based on the fact that both microclimate and the drought sensitivity of stemwood production were earlier shown to differ with stand size and isolation in this ecotone. Contrary to our hypothesis, we did not find significant differences in the organic carbon stock densities of the tree biomass and the mineral soil. The depth, carbon content and carbon stock density of the organic layer increased with stand size, but was not a major determinant of total ecosystem carbon stock density. Nevertheless, the increasing depth and the increasing humus content of the organic layer with stand size could be significant by improving moisture availability and, thus, promoting forest regeneration. Furthermore, reduced organic layer thickness and humus content and thus water storage capacity could be one out of several causes of the previously observed higher drought vulnerability of stemwood formation in small forest stands of the Mongolian forest-steppe. A mean carbon stock density of 237 Mg C ha−1 for total ecosystem organic carbon stock density matches with earlier estimates for Mongolia's boreal forest corroborating the view that the ecosystem carbon pool density at the southern edge of the boreal forest is lower compared to forests at higher latitudes with even colder climate and deeper and more widespread permafrost. [ABSTRACT FROM AUTHOR]

Highlights • Reductions in stand density improve post drought growth resilience. • Drought resistance is higher in P. sylvestris than in P. nigra in heavily thinned stands. • Water-use efficiency is negatively related to thinning intensity. • Thinning makes plantations less vulnerable to drought. Abstract Previous research has provided insights into the potential response of growth and water use efficiency to thinning in Mediterranean forests, but little is known about the potential benefits of silviculture for plantations under severe drought stress. We selected two stands of Pinus sylvestris L. and P. nigra Arnold., and used dendrochronology and carbon isotopes (δ13C) to understand the growth and functional responses of high-density planted pine forests to thinning in drought-prone areas. Resistance, recovery, and resilience indices were calculated for each species using BAI data. We expected heavy thinning to produce stands that were more resilient to drought, particularly for the more drought-tolerant P. nigra. Differences in the basal area increments (BAI) and intrinsic water-use efficiency (iWUE) were found between the unthinned stand and the thinned stands, for both species. After thinning, BAI decreased as iWUE increased but this relationship was only marginally significant in P. sylvestris. Thinning increased growth resistance, recovery, and resilience following the severe drought of 2012. Our findings suggest that water shortage, linked to recurrent droughts, together with high tree competition, negatively affected tree growth and increased iWUE, which explains the dieback of some of these pine plantations. We evidence the vulnerability of densely planted Mediterranean pines to the forecasted warmer and drier conditions. These results show that a heavy thinning treatment (60% of basal area removed) provides a promising silvicultural framework for the adaptation of these drought-sensitive Mediterranean mountain pine forests to the potential risks of climate change. [ABSTRACT FROM AUTHOR]

Highlights • Haloxylon ammodendron was found to be less drought-resistant than H. persicum. • Haloxylon ammodendron was groundwater dependent, but H. persicum was not. • Declining groundwater depths induced the water-carbon imbalance of H. ammodendron. • The two species converted to deeper, but different water sources during extreme drought. Abstract In the context of global change, frequent extreme droughts and artificial groundwater overexploitation have significantly changed water availability, which will have profound effects on ecosystem water balance and plant survival. However, few studies have explored the changes in physiology and water-use of desert plants caused by these emerging variations in water availability. Therefore, we investigated the photosynthesis, water potential, and water absorption of two dominant woody species (Haloxylon ammodendron and H. persicum) at three sites with different groundwater depths in the Gurbantunggut Desert of Central Asia during an extreme drought period. Our results showed that: (1) H. ammodendron exhibited more negative pre-dawn leaf water potential and lower photosynthetic capacity (–2.85 MPa, 24.19 μmol CO 2 m−2 s−1) than H. persicum (–2.31 MPa, 33.92 μmol CO 2 m−2 s−1) during the extreme drought period; (2) pre-dawn leaf water potential and carbon assimilation of H. ammodendron significantly decreased with declining groundwater depths, whereas those of H. persicum were barely affected; (3) both species converted to deeper but different water sources during the extreme drought period: H. ammodendron obtained 56–100% soil water from the near-groundwater layer, while H. persicum obtained 64–100% soil water from the deep soil layer; (4) the depths of water absorption constantly deepened with declining groundwater depths. Variations in water availability have led to the adjustment in plant water uptake, but this adjustment was not sufficient for the optimal physiological performance of H. ammodendron. Thus, under more intense and frequent drought events, further declines in groundwater depth could significantly inhibit growth of this species and may ultimately threaten its survival. Our findings on water use and physiological responses of dominant plant species to decreasing water availability provide a basis for predicting the future of desert plants under deteriorating water conditions. [ABSTRACT FROM AUTHOR]

Highlights • K step appeared in OJIP transient and ET 0 /RC, ET 0 /CS 0 , φE 0 of rice seedlings were decreased under drought stress. • Si treatment delayed chlorophyll-protein complexes degradation of rice seedlings under stress. • Si treatment altered the thylakoid protein components under drought stress. • Si treatment maintained photosynthetic performance by improving light energy absorption and transformation. Abstract For revealing the internal mitigation mechanism of silicon to drought stress, a super high-yield hybrid rice LYP9 was employed to study the change of photosynthetic fluorescence, structure and composition of thylakoid membrane as well as its physiological property by polyethylene glycol (PEG) and silicon (Si) treatment. Results showed that K step appeared in OJIP transient and ET 0 /RC, ET 0 /CS 0 , φE 0 of rice seedlings were decreased under drought stress, while these parameters were increased by applying silicon. We found that silicon application could relieve the degradation of membrane protein complexes under drought condition, such as supercomplexes, PSI core binding LHCI, PSI core, F 1 -ATPase binding Cyt b 6 /f complex, PSII core, trimeric LHCII and monomeric LHCII. Thylakoid membranes proteins were further detected by BN-SDS-PAGE, 20 differential protein spots between PEG treatment and PEG treatment applying with silicon were identified. These alterations were involved in light harvesting, stability of PS I, function of PS II reaction centers, electron transport, PS II core antenna content, and consequent synthesis of ATP. Our results indicated that Si treatment might play roles in absorption, transformation and transfer of light energy by optimizing the thylakoid membrane protein components in rice seedlings under drought stress observed by BN-PAGE and BN-SDS-PAGE. [ABSTRACT FROM AUTHOR]

Highlights • PF, DF and P700 revealed complementary information on drought-induced changes. • Drought impaired OEC, PSII RCs and PSI acceptor side in maize photosynthetic chain. • Drought decreased maize photosynthetic forward, backward and cyclic electron flows. • Cyclic electron flows might play an important role in maize response to drought. Abstract The effect of drought on the prompt chlorophyll a fluorescence (PF) transient (OJIP), delayed chlorophyll a fluorescence (DF), modulated 820-nm reflection (MR), energy conversion efficiencies in photosystems (PS) I and II, and cyclic electron flow (CEF) activity in two maize hybrids with contrasting drought tolerance was investigated. Our aim was to identify the target site of drought stress on the photosynthetic electron transport chain and investigate the relevance of the CEF pathway to the drought tolerance of maize plants. The OJIP analysis showed that drought stress, depending on its duration, decreased F P , increased F J , and induced a pronounced K-band and a positive L-band. Moreover, OJIP parameters, including PI ABS , RC/CS O , TR O /ABS, and ET O /TR O , were significantly reduced. The DF analysis showed that the values of I 1 and I 2 in the induction curve and L 1 and L 2 derived from the decay curve decreased progressively with the duration of drought stress. The MR analysis showed that drought stress inactivated both the fast decrease and slow increase phases of the MR transient, resulting in a gradual decrease in both V PSI and V PSII-PSI. The energy conversion analysis showed that drought stress decreased the PSI photochemical quantum yield Y(I) and PSII photochemical quantum yield Y(II). Compared to the tolerant hybrid, the drought-induced changes in the sensitive hybrid were stronger and appeared at an earlier treatment stage. The CEF activity analysis showed that the CEF pathway under drought stress operated for a longer time in the tolerant hybrid than that in the sensitive hybrid. The above results indicate that drought stress damaged the donor and acceptor sides of PSII, the PSII reaction center and the acceptor side of PSI and decreased the efficiency of both PSI and PSII and the capacity of electron transfer. The CEF pathway might play an important role in the tolerance of the maize photosynthetic electron transport chain to drought stress. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Proteomics has coupled with morpho-physiology of drought sensitive and resistant parents to define the resistant traits of their progenies. • DAPs in leaf of parents and progeny F6, shed light on the inheritance of the molecular characters that lead to resistance. • The experimental design with proteomic approach might build a complimentary method for future marker-assisted selection of drought resistance. Abstract Comparative physiological and proteomic analyses of two wheat cultivars Arg (resistant to drought), Arta (sensitive to drought) and four F6 lines (B1, B2, W1, W2) derived from their crossbreed lead us to discriminate the Arg, B1 and B2 lines to be resistant toward strong leaf water deficit. Proteins belonging to carbon metabolism, photosynthesis and detoxification/defense showed the major change. Tolerant Arg showed the accumulation of stress-responsive proteins under drought stress higher than in sensitive Arta. The high level of Cu/Zn superoxide dismutase, and two chloroplastic encoded enzymes indicate that their accumulation might improve stress resistance. Morphological and physiological traits of B1 and B2 confirmed that these lines are tolerant to drought stress. Proline and MDA contents are higher and lower, respectively, in these two lines than in other ones. This act synergistically with the modulation of primary metabolisms and protection against dehydration and oxidative damage resulting in the improvements of survival of the seedlings, greater vegetative vigor and productive capacity that also exceeds that of the tolerant Arg parental line. For all these evidences, the B1 and B2 progenies could be selected as the best lines in the future cultivation trials for wheat breeding under moderate and severe drought conditions. [ABSTRACT FROM AUTHOR]

Highlights • Drought stress decreases growth and secondary metabolites in Glycyrrhiza uralensis. • Bacillus pumilus improves the growth and the antioxidant activities of plant. • B. Pumilus increases secondary metabolites content and the gene expression of key enzymes for glycyrrhizic acid synthesis. Abstract Drought is a major limiting factor of plant productivity worldwide and its incidence is predicted to increase with climate changing. Endophytes are non-pathogenic plant-associated bacteria that can play an significant role in improving plant tolerance to drought. Here, the effects of Bacillus pumilus (B. pumilus) inoculation on growth, metabolite accumulation and related protein expression, and it's mechanism focusing on antioxidant defense of Glycyrrhiza uralensis Fisch. (G. uralensis) subjected to drought stress were investigated under controlled conditions. Drought stress induced oxidative damage and further decreased growth and secondary metabolites in G. uralensis. Exposure of inoculated plant to drought-stress led to significant increase in total biomass by 34.9%, and in oxygen species and antioxidants while decrease in lipid peroxidation level, compared to non-inoculated plants grown under similar conditions. There was a significant effect of the endophyte on plant metabolism; higher levels of total flavonoids, total polysaccharide and glycyrrhizic acid were recorded in roots of colonized plants compared to non-colonized ones. Furthermore, the expression of HMGR, SQS and β-AS, key enzymes for glycyrrhizic acid synthesis, significantly increased by B. pumilus inoculation. Taken together, our results indicated that B. pumilus improves G. uralensis growth under drought stress through the modification of antioxidants accumulation and enhances glycyrrhizic acid content by the incremental expression of key enzymes. These results will contribute to the development of a microbial agent to improve the yield and quality of medical plants exposed to environmental stresses. [ABSTRACT FROM AUTHOR]

Highlights • Cultivar mixtures can manage the dilemma of flowering too late or too early. • A mixture of a long and mid-duration cultivar was consistently high yielding. • In one experiment cultivar mixtures yielded 6.4% more than single cultivars. • Research needs to identify cultivars and agronomy to maximise over-yielding. Abstract Mixtures of wheat cultivars of different duration can potentially balance the yield-reducing risks of frost, heat and terminal drought. Cultivar mixtures with contrasting duration were tested across three experiments in Western Australia. Experiment 1 consisted of three sowing dates (early, mid and late), experiment 2 consisted one sowing date and experiment 3 consisted of two sowing dates (early and late). The three experiments and the multiple sowing dates created differences in the exposure to frost, heat and terminal drought risk. Seven treatments were established in each environment, consisting of three commercially-available cultivars (long, mid and short-duration); together with each of the two- and three -cultivar mixtures of these cultivars. In experiment 1 yields of the single cultivars showed the expected pattern with the long duration cultivar having the highest yield when sown early and the short duration cultivar having the higher yield when sown late. There were few differences in yield in experiments 2 and 3. Only a single treatment, a mixture of the long and mid-duration cultivars, was either the highest yielding or not significantly different from the highest yielding across all environments. In experiment 1 there was evidence of over-yielding with the mean of all the mixtures being 6.4% greater (P = 0.043) than the mean of the individual cultivars across the three sowing dates. This research has demonstrated that wheat cultivar mixtures can stabilise the combined risks of frost, heat and drought stress in frost and heat-prone dryland environments, providing growers with a strategy to manage these uncertain risks. [ABSTRACT FROM AUTHOR]

Highlights • Effect of biochar on mitigating the adverse effects of drought on soybean was evaluated. • Application of 1.25%wt was the most appropriate level of cattle manure biochar. • High levels of biochar decreased almost all agronomic traits and yield components. • Drought decreased all agronomic traits and yield components except greenness index. • Effect of drought on stomatal conductance was more severe at reproductive stage. Abstract Drought and low amounts of organic matter are two main constraints when considering agriculture in arid and semiarid regions. The two constraints and their adverse effects on soils and plants may be alleviated by biochar (B). Therefore, this study aimed to evaluate the influence of 0 (0B), 1.25 (1.25B), 2.5 (2.5B) and 5% wt (5B) cattle-manure biochar on the agronomic and physiological traits of soybean under field capacity (FC), 0.7FC and 0.55FC conditions. Drought was observed to reduce water use efficiency (WUE), leaf area, stomatal conductance (SC), harvest index (only for 0.55FC), straw fresh matter yield (SFMY), straw dry matter yield (SDMY), pod yield, grain yield, pod lenght, and plant height by nearly 15–16%, 23–36%, 23–47%, 11–12%, 42–64%, 36–52%, 44–65%, 41–64%, 5–11%, and 33–60%, respectively as compared with those of control (FC conditions), whereas drought increased the greenness index (GI) of soybean leaves by 11–20% compared with control. In general, drought decreased all traits of studied soybean variety. However, pod yield, grain number, SFMY and plant height were more negatively influenced. The most unfavorable effect of drought on SC was observed at the late reproductive stage (90 days after planting, DAP); whereas, drought effects on leaf area were similar at different growth stages. Harvest index (HI) and WUE was the lowest at severe drought (0.55FC) and there was no significant difference between these traits at non-drought (FC) and moderate drought (0.7FC) conditions. Therefore, keeping soil moisture to near 0.7FC not only did not change the WUE and HI, but also reduces water consumption. All B treatments increased the leaf area (at the beginning, 60 DAP and middle reproductive stages, 75 DAP), GI and SC by 6–36%, 11–20%, and 46–80%, respectively. The application of 1.25B increased WUE, SFMY, SDMY, the pod length and plant height by 26%, 35%, 27%, 5%, and 16%, respectively, whereas higher percentages of B were ineffective, i.e. 2.5B did not significantly affect the WUE, SDMY and pod length and 5B reduced the values of the grain and pod yield and 1000-grain weight. Low level of biochar (1.25B) had positive influences on almost all traits; whereas, higher levels (2.5B and 5B) due to the excessive salinity not only had no positive effects but also adversely influenced almost all traits. Furthermore, positive effects of the effective biochar treatment (1.25B) on almost all traits were most pronounced at the moderate or severe drought conditions compared with non-drought conditions. In conclusion, high levels of B due to salinity related negative influences on plant cannot be suggested. While, application of 1.25B due to mitigating the adverse effects of drought and consequently increasing WUE, the growth and yield components of soybean may be recommended. [ABSTRACT FROM AUTHOR]

Highlights • This is the first report of Withania coagulans response to G × E interaction. • Distance between stress time and photosynthesis indices measurements is important. • Values for F v / F m in Fanuj, F 0 and ФPSII decreased with increasing stress severity. • Photosynthesis rate declined and leaf greenness increased with the onset of drought. • According to results, W. coagulans can be called "Xerophytes Camel". Abstract Withania coagulans is one of the most important medicinal species of the Solanaceae which has pharmacological properties for future research in drug development. Photosynthesis and morphological parameters in response to drought of this species have not been investigated as yet, though the issue is of interest. The factorial combination of four water deficit stress (20% (un-stressed control), 30%, 40% and 50% of FC depletion) and four landraces of W. coagulans (Fanuj, Khash, Saravan and Sarbaz) were laid out in a randomized complete design in a phytotron over the course of 180 days. The first, second, third and fourth samplings were performed every 45 day after imposing the treatments (DAT). The results demonstrated that increase in the water deficit stress levels, decreased minimal fluorescence (F 0), leaf greenness, photosynthesis rate, plant height, leaf area, dry weight and quantum yield of PSII photochemistry)Ф PSII (in all landraces and maximum photochemical efficiency of PSII (Fv/Fm) in Fanuj, but increased non-photochemical quenching) NPQ (and Fv/Fm in Saravan and Sarbaz landraces. The W. coagulans landraces such as Fanuj with the highest vector loadings of Ф PSII at 135 and 180 DAT and F v /F m at 45 DAT and Sarbaz with the highest vector loading of F 0 at 45 DAT were found suitable for unstressed and severe stress conditions, respectively. Among the chlorophyll fluorescence and morphological parameters, total dry weight had the significant positive correlations with plant height, leaf area and F 0 at 45 DAT. Thus, this study indicated chlorophyll florescence should be measured at different phases and future studies should focus on the sensitivity of these parameters to detect potential times among subjects of different stresses. These parameters are easy, cheap, efficient and reliable physiological characteristics which can be used to guide the breeding of new resistant genotypes. According to results, W. coagulans can be called "Xerophytes Camel". [ABSTRACT FROM AUTHOR]

Abstract Drought stress is one of most dramatic abiotic stresses, reduces crop yield significantly. Application of hormones proved as an effective drought stress ameliorating approach. 24-Epibrassinolide (EBL), an active by-product from brassinolide biosynthesis increases drought stress tolerance in plants significantly. EBL application enhances plant growth and development under drought stress by acting as signalling compound in different physiological processes. This article discussed potential role of 24-epibrassinolide application and drought tolerance in plants. Briefly, EBL sustains or improves plant growth and yield by enhancing carbon assimilation rate, maintaining a balance between ROS and antioxidants and also plays important role in solute accumulation and water relations. Furthermore, we also compared different EBL application methods and concluded that seed priming and foliar application are more productive as compared with root application method. In conclusion, EBL is very impressive phyto-hormone, which can ameliorate drought stress induced detrimental effects in plants. Highlights • 24-Epibrassinolide (EBL) is an important brassinosteroid, plays a very important role in plant metabolism. • EBL improves plant growth and yield by improving morphological growth of plants under drought stress. • EBL improves photosynthesis by improving chlorophyll fluorescence, and other leaf gas exchange traits. • EBL plays a crucial role as in redox regulation under drought stress. • EBL application by seed priming and foliar application is more effective as compared with root application. [ABSTRACT FROM AUTHOR]

Abstract Drought is one of the major abiotic stress factors that affect grape growth and yield, which in turn negatively affects the grape and wine production industry. Developing effective approaches to improve grapevine tolerance to drought stress is a priority for viticulture. Strigolactones, a newly discovered class of carotenoid-derived phytohormones, have been found to participate in various physiological processes. Herein, the effect of strigolactones (SLs) on grape seedlings under drought stress was investigated. Two-year-old grape seedlings (Vitis vinifera L.) were sprayed with 3 doses of rac -GR24 (1 μM, 3 μM and 5 μM), a synthesized strigolactone, and then were subjected to 7% (w/v) polyethylene glycol (PEG-6000) to simulate the drought conditions. Synthetic GR24 treated plants showed higher tolerance to drought stress with regard to lower electrolyte leakage, stomatal opening, reactive oxygen species (ROS), and higher relative water content, chlorophyll content, photosynthesis rate and malondialdehyde (MDA) content. GR24 application also decreased the levels of indoleacetic acid (IAA) and zeatin riboside (ZR), while increasing the level of abscisic acid (ABA), both in the roots and leaves under drought stress. These results suggested that foliar application of GR24 could ameliorate the adverse effects of drought due to its regulation of stomatal closure through ABA or ROS, and modulation of chlorophyll components and photosynthesis, as well as activation of the antioxidant defense capacity. Cross-talk with other hormones, especially ABA, was also suggested to be one of the important mechanism during this process. This study contributes to our current understanding of GR24-induced drought tolerance in grapevines. Highlights • GR24 pretreatment alleviates the adverse effects of drought stress in grape seedlings. • Under drought stress, GR24 could better induce the stomatal closure. • GR24 could modulate the chlorophyll components and dampened the decrease of photosynthesis induced by drought. • Cross-talk of SLs with other hormones, especially ABA, may be one of the important mechanism in drought response. • This is the first attempt for SLs to be used in horticultural fruit tree-grape. [ABSTRACT FROM AUTHOR]

Abstract Drought stress is a serious threat to agriculture and the environment. Brassinosteroids (BRs) increase tolerance to drought stress of plant. Autophagy plays important roles in plant responses to drought stress; however, there are few reports on autophagy in peach (Prunus persica). In total, 23 putative autophagy-related genes (ATG s) in peach were identified using ATG s from the Arabidopsis thaliana genome as query in BLASTx algorithm-based searches. Under drought stress, the photosynthetic abilities of peach leaves decreased, while antioxidant enzyme activities, autophagy and ATG expression increased. A correlation analysis showed that antioxidant enzyme activities are inversely correlated to the expression levels of the PpATG s. During drought, the PpATG8 s and some PpATG18s had the strongest responses. To investigate enhanced drought-stress tolerance, peach was treated with water, 100 nM 24-epibrassinolide (EBR), 1 μM EBR, 10 μM EBR and 1 μM voriconazole. Exogenous EBR at 1 μM decreased the malondialdehyde (MDA) content under drought stress when compared with water-, 1 μM voriconazole-, 100 nM EBR- and 10 μM EBR-treated peach leaf. The 1-μM EBR application increased superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX) and glutathione peroxidase (GR) activities during drought stress. In addition, the expression levels of PpATG s were inhibited by EBR. Thus, the 1-μM EBR treatment alleviated drought-stress damage to peach leaves, decreased PpATG expression levels and reduced the number of autophagosomes. Highlights • Autophagosomes can respond to drought stress in peach leaves. • PpATG8 and PpATG18 respond most strongly during drought. • Antioxidant enzyme activities are inversely correlated to PpATG expression. • A 24-epibrassinolide treatment relieved drought stress and reduced autophagosomes. [ABSTRACT FROM AUTHOR]

Abstract The aim of this study was to assess some physiological parameters and anatomical changes in two wheat plant cultivars (Triticum aestivum L. cvs. Sakha 93 and Sids 9) in response to irrigation with magnetized water under two levels of drought stress (field capacity (FC) of 75% and 50%) and the control (FC 100%) in two consecutive winter growing seasons (November 20 to May 5 2014/2015 and 2015/2016). Pot experiments were carried out in a greenhouse in the experimental farm of the Faculty of Agriculture, Menoufia University, Shibin El-Kom, Egypt. A water deficit, particularly at 50% FC, significantly decreased growth and parameter values, above all in Sakha 93, and disrupted most physiological aspects, biochemical constituents and internal structural features of both wheat cultivars. Irrigation with magnetized water alleviated the negative consequences of drought stress on most physiological and biochemical parameters to a variable extent: the whole plant dry weight, total water content, total soluble sugar concentration in leaves, total free amino acids and proline increased by about 32, 12, 17, 27 and 73%, respectively, under 50% FC drought stress in Sids 9 compared to the control. As the levels of drought increased, the grain yield (g/plant) decreased considerably, from about 81% in Sakha 93 at 50% FC to 26% in Sids 9 at 75% FC. The use of magnetic water increased grain yield from 61% in Sakha 93 at 75% FC to about 268% in Sids 9 at 50% FC. Magnetic water also increased the thickness of the flag leaf midvein and lamina, as well as the metaxylem vessel diameter of Sakha 93 by 28.8, 11.7 and 20.0%, respectively, compared to the control. The application of magnetic water increased the growth and the other parameter values studied in both cultivars but above all in Sakha 93, whereas Sids 9 produced more grain yield under all levels of drought stress. As the growth and grain production increased in both cultivars when using magnetic water, this study recommends this type of irrigation for these wheat plants, which are widespread in Egypt. Highlights • Irrigation with Magnetic Water alleviated drought stress. • Wheat cultivars irrigated with Magnetic Water increased grain yield. • In wheat plants irrigation is reduced more than 25% using Magnetic Water. [ABSTRACT FROM AUTHOR]

Abstract Apocynum venetum is an eco-economic plant species with high adaptability to saline and arid environments. Our previous work has found that A. venetum could absorb large amount of Na+ and maintain high K+ level under saline conditions. To investigate whether K+ and Na+ could simultaneously enhance drought resistance in A. venetum , seedlings were exposed to osmotic stress (−0.2 MPa) in the presence or absence of additional 25 mM NaCl under low (0.01 mM) and normal (2.5 mM) K+ supplying conditions, respectively. The results showed that A. venetum should be considered as a typical K+-efficient species since its growth was unimpaired and possessed a strong K+ uptake and prominent K+ utilization efficiency under K+ deficiency condition. Leaf K+ concentration remained stable or was even significantly increased under osmotic stress in the presence or absence of NaCl, compared with that under control condition, regardless of whether the K+ supply was sufficient or not, and the contribution of K+ to leaf osmotic potential consistently exceeded 37%, indicating K+ is the uppermost contributor to osmotic adjustment of A. venetum. Under osmotic stress, the addition of 25 mM NaCl significantly increase Na+ accumulation in leaves and the contribution of Na+ to osmotic adjustment, thus improving the relative water content, concomitantly, promoting the photosynthetic activity resulting in an enhancement of overall plant growth. These findings suggested that, K+ and Na+ simultaneously play crucial roles in the osmotic adjustment and the maintenance of water status and photosynthetic activity, which is beneficial for A. venetum to cope with drought stress. Highlights • Apocynum venetum is a typical K+-efficient desert plant with high K+-uptake and -utilization efficiencies. • Large accumulation of K+ to improve osmotic adjustment is vital for A. venetum to cope with osmotic stress. • Moderate NaCl could substantially enhance leaf photosynthesis and hydration of A. venetum under osmotic stress. [ABSTRACT FROM AUTHOR]

Highlights • Differences exist between the performances of various drought indices used to identify drought impacts on crop yields. • Multiscalar drought indices outperform uniscalar drought indices for monitoring the impact of drought on crop yields. • Shorter drought time-scales are better at identifying drought impacts on crop yields. Abstract This article presents an analysis of the response of the annual crop yield in five main dryland cultivations in the United States to different time-scales of drought, and explores the environmental and climatic characteristics that determine the response. For this purpose we analysed barley, winter wheat, soybean, corn and cotton. Drought was quantified by means of the Standardized Precipitation Evapotranspiration Index (SPEI). The results demonstrate a strong response in the interannual variability of crop yields to the drought time-scales in the different cultivations. Moreover, the response is highly spatially variable. Crop types showed considerable differences in the month in which their yields are most strongly linked to drought conditions. Some crops (e.g. winter wheat) responded to drought at medium to long SPEI time-scales, while other crops (e.g. soybean and corn) responded to short or long drought time-scales. The study confirms that the differences in the patterns of crop yield response to drought time-scales are mostly controlled by average climate conditions, in general, and water availability (precipitation), in particular. Generally, we found that there is a weaker link between crop yield and drought severity in humid environments and also that the response tends to occur over longer time-scales. [ABSTRACT FROM AUTHOR]

Highlights • Mild salt and drought stress improve strawberry fruit functional quality. • ABA metabolism and of its derivatives was affected by mild salt (SS) and drought (DS) stresses. • The mild stress applied did not reduce fruit yield. • Application of mild DS and SS may serve as an effective strategy to improve functional quality. Abstract Strawberry crop is very sensitive to osmotic stress conditions. We investigated the effect of the stress induced by mild drought (DS) and salt (SS) stresses, on molecular, physiological, and metabolic processes in the strawberry crop (Fragaria ananassa), cv. Camarosa. The results showed that the fruit yield was not affected. Mild DS and SS also resulted in an increased content of phenolics, anthocyanins, and l -ascorbic acid, and an increased antioxidant activity. These effects were accompanied by increased levels of ABA and its derivatives (phaseic and dehydrophasic acids), alongside the upregulation of several genes involved on their synthesis. Therefore, the results obtained in this study suggest that mild DS and SS improve the functional quality of strawberry fruits through and ABA-dependent mechanism. [ABSTRACT FROM AUTHOR]

Highlights • AM fungi improve plant roots development even under drought stress conditions. • AM fungi increase glomalin-related soil protein content and hyphal length. • AM fungi enhance the stability of soil water-stable aggregates. • Mycelium network directly contribute to the bond energy of soil macroaggregates. Abstract Arbuscular mycorrhizal (AM) fungi have a direct influence on soil aggregation in most fertile ecosystems. This study investigated the effects of AM fungi on soil aggregate stability of Calcaric Regosol under well-watered and drought stress conditions. A two-compartment system was employed to exclude the effects of plant roots, and ultrasonic dispersion technique was applied to evaluate the aggregate bond energy. The results showed that good symbiotic relationships were formed between AM fungi and sandstorm-tolerant species Astragalus adsurgens Pall even under drought stress conditions. Inoculation with AM fungi significantly improved plant growth, especially the root development. Hyphal length, spore density, glomalin-related soil protein content were significantly increased by AM fungal inoculation under both well-watered and drought stress conditions. Likewise, the proportion and dispersive energy of soil water-stable macroaggregates were also markedly increased by the inoculation. The hyphae of AM fungi directly contributed to the dispersive energy of soil water-stable macroaggregates and significantly improved soil aggregate stability under both experimental conditions. This study demonstrates that AM fungi play a dominant role in the stability of soil water-stable aggregates by improving the aggregate bond energy, particularly for macroaggregates. [ABSTRACT FROM AUTHOR]

Highlights • PSII photochemistry efficiency were monitored over an entire leaf-life span. • PSII photochemistry dropped only with severe drought episode. • Photoprotection occurred through heat dissipation strategies with drought episode. • Rewatering did not enhance the photoprotection with leaf aging. Abstract Plant growth and photosynthesis in response to water status have been extensively investigated. However, elucidating the photosynthetic process and its indicators under a drought episode and rewatering across the entire leaf lifespan is often neglected. In this experiment, three water treatments were set during two growth seasons: a control treatment, moderate persistent drought (T 1), and severe persistent drought (T 2). Maize leaf chlorophyll fluorescence emission was analyzed to determine the regulative responses of the photosynthetic potentials and photosystem II (PSII) photochemistry process to drought and rewatering in situ. A severe drought episode during the peak vegetative growth stage resulted in decreases in chlorophyll content, the maximal efficiency of PSII photochemistry (F v / F m), and photochemical quenching, but increases in non-photochemical quenching and the yield for dissipation by downregulation. Rewatering only restored partial PSII functions in plants that had undergone historical drought episodes. An analysis of non-photochemical pathways of thermal dissipation indicates that regulative photoprotection of the photosystem apparatus may occur through heat dissipation when an effect of severe drought episode appeared on a young leaf; however, rewatering did not enhance photoprotection with leaf aging. Compared to the control treatment, the yield of T 1 and T 2 decreased by 25.1% and 27.1% in 2015, and 26.4% and 54.3% in 2016, respectively. The chlorophyll content was significantly and closely correlated with F v / F m (R = 0.65, P < 0.001) and the maximum versus minimum fluorescence yield in the dark-adapted state (F m / F o) (R = 0.72, P < 0.001). Additionally, the two parameters can be suggested to feasibly track chlorophyll content changes and the degree of leaf senescence in responses to a drought episode and its interaction with leaf aging: F m / F o and the relative limitation to photosynthesis (RLP). The current results may provide a profound insight into better understanding the underlying mechanism of photosynthetic potentials and photochemistry efficiency and photoprotection in response to drought episodes and rewatering over the entire leaf lifespan. [ABSTRACT FROM AUTHOR]

Highlights • A total of 19 QTLs were stable under both well-watered and water-limited regimes. • Three QTLs for well-watered and two for water-stress conditions were detected in both locations. • Domestication and breeding have resulted in the low genetic diversity of cultivated cotton lines. Abstract Cotton is an economically important commodity for nearly fifty industries including the textile sector which is largely based on cotton fiber. Identification of markers linked to loci for fiber traits under drought stress may be particularly beneficial because such loci could provide the genetic adaptability needed to produce good fiber under water limitation. In the present study, 177 simple sequence repeat (SSR) markers were used to detect significant quantitative trait loci (QTLs) linked to 11 fiber quality and plant structure traits in a panel of 99 Upland cotton (Gossypium hirsutum L.) genotypes using GLM and MLM analysis. The fiber quality traits, including fiber length (FL), fiber fineness (FF), fiber strength (FS), fiber elasticity (FE), fiber uniformity (FU), spinning conversion index (SCI), earliness (EAR), 1st position boll retention (1st PBR), 2nd position boll retention (2nd PBR), total boll number (TBN) and plant height (PH), were tested under both well-watered and water-limited irrigations in two locations. At both locations, GLM identified a total of 74 and 70 QTLs under well-watered and water limited conditions, respectively, at p ≤ 0.005. MLM detected seven and 23 QTLs under well-watered and water-limited conditions, respectively. Of the identified QTLs, some QTLs were detected in both locations: three for well-watered and two for water-stress conditions. Moreover, a total of 19 QTLs were stable under both watering-regimes. The QTLs identified herein could be useful in the development of cotton cultivars that have adaptability to drought conditions worldwide. [ABSTRACT FROM AUTHOR]

Abstract AtUBC32, AtUBC33, and AtUBC34 comprise Arabidopsis group XIV E2 ubiquitin-conjugating enzymes. Yeast two-hybrid, in vitro pull-down, and bimolecular fluorescence complementation assays revealed that group XIV E2s are interacting partners of the U-box-type E3 ligase PUB19, a negative regulator of drought stress response. These three AtUBCs are co-localized with PUB19 to the punctae-like structures, most of which reside on the endoplasmic reticulum membrane of tobacco leaf cells. Suppression of AtUBC32 , AtUBC33 , and AtUBC34 resulted in increased abscisic acid-mediated stomatal closure and tolerance to drought stress. These results indicate that Arabidopsis group XIV E2s play negative roles in drought stress response. [ABSTRACT FROM AUTHOR]