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Water deficit episodes impact apple (Malus domestica) productivity through challenging the trees' water status, the influence of extreme high temperature climate has become increasingly prominent in recent years. Rootstocks can bestow specific properties on the fruit trees such as the resistance to drought stress. However, the related hydraulic mechanisms in response to water deficit have not been fully understood. Herein, five rootstocks (SH6, GM256, M9, M26, and MM106) were examined under water limitation. The hydraulic conductance of root (Kroot), shoots (Kshoot), and stems (Kstem-shoot) in the five rootstocks reduced slightly during drought stress. Whereas the leaf water potential and photosynthesis of five rootstocks decreased dramatically when they were exposed to drought stress. Additionally, the Kshoot and Kstem-shoot were strongly correlated with the total plant leaf area. Aquaporins (AQPs) involved in the symplastic water transport pathway, the PIP2:1, TIP1:1, and TIP2:2 mRNA levels of all genotypic rootstocks showed significant regulation under drought stress. We examined the relationships among photosynthesis, apoplastic, and symplastic water movement pathways to achieve a comprehensive understanding of rootstocks' hydraulic strategy for improving drought adaptation. The PIP2:1 and TIP2:1 in leaves were more sensitive to root hydraulic conductance in response to drought stress. Furthermore, the coordinated relationship existed in leaf-specific conductance of shoot (K l -shoot) and transpiration rate (Tr) under drought stress in the rootstocks. Overall, the drought resistance in the five dwarfing rootstocks is associated with the rapid re-establishment of water-related traits, and the effect of the canopy on the drought resistance in apple rootstocks merits much more attention., (© 2023 Scandinavian Plant Physiology Society.)

In trees, nonstructural carbohydrates (NSCs) serve as long-term carbon storage and long-distance carbon transport from source to sink. NSC management in response to drought stress is key to our understanding of drought acclimation. However, the molecular mechanisms underlying these processes remain unclear. By combining a transcriptomic approach with NSC quantification in the leaves, stems, and roots of Populus alba under drought stress, we analyzed genes from 29 gene families related to NSC signaling, translocation, and metabolism. We found starch depletion across organs and accumulation of soluble sugars (SS) in the leaves. Activation of the trehalose-6-phosphate/SNF1-related protein kinase (SnRK1) signaling pathway across organs via the suppression of class I TREHALOSE-PHOSPHATE SYNTHASE (TPS) and the expression of class II TPS genes suggested an active response to drought. The expression of SnRK1α and β subunits, and SUCROSE SYNTHASE6 supported SS accumulation in leaves. The upregulation of active transporters and the downregulation of most passive transporters implied a shift toward active sugar transport and enhanced regulation over partitioning. SS accumulation in vacuoles supports osmoregulation in leaves. The increased expression of sucrose synthesis genes and reduced expression of sucrose degradation genes in the roots did not coincide with sucrose levels, implying local sucrose production for energy. Moreover, the downregulation of invertases in the roots suggests limited sucrose allocation from the aboveground organs. This study provides an expression atlas of NSC-related genes that respond to drought in poplar trees, and can be tested in tree improvement programs for adaptation to drought conditions., (© 2023 The Authors. Physiologia Plantarum published by John Wiley & Sons Ltd on behalf of Scandinavian Plant Physiology Society.)

Many degraded ecosystems have altered nutrient dynamics due to invaders' possessing a suite of traits that allow them to both outcompete native species and alter the environment. In ecosystems where invasive species have increased nutrient turnover rates, it can be difficult to reduce nutrient availability. This study examined whether a functional trait-based restoration approach involving the planting of species with conservative nutrient-use traits could slow rates of nutrient cycling and consequently reduce rates of invasion. We examined a functional trait restoration initiative in a heavily invaded lowland wet forest site in Hilo, Hawai'i. Native and introduced species were chosen to create four experimental hybrid forest communities, in comparison to the invaded forest, with a factorial design in which communities varied in rates of carbon turnover (slow or moderate [SLOW, MOD]), and in the relationship of species in trait space (redundant or complementary [RED, COMP]). After the first 5 years, we evaluated community-level outcomes related to nutrient cycling: carbon (C), nitrogen (N), and phosphorus (P) via litterfall, litter decomposition, and outplant productivity and rates of invasion. We found that (1) regardless of treatment, the experimental communities had low rates of nutrient cycling through litterfall relative to the invaded reference forest, (2) the MOD communities had greater nutrient release via litterfall than the SLOW communities, (3) introduced species had greater nutrient release than native species in the two MOD experimental communities, and (4) within treatments, there was a positive relationship between nutrient levels and outplant basal area, but outplant basal area was negatively associated with rates of invasion. The negative relationships among basal area and weed invasion, particularly for the two COMP treatments, suggest species existing in different parts of trait space may help confer some degree of invasion resistance. The diversification of trait space was facilitated by the use of introduced species, a new concept in Hawaiian forest management. Although challenges remain in endeavors to restore this heavily degraded ecosystem, this study provides evidence that functional trait-based restoration approaches using carefully crafted hybrid communities can reduce rates of nutrient cycling and invasion in order to reach management goals., (© 2023 The Ecological Society of America.)

Carbon isotope composition of tree-ring (δ 13 C Ring ) is a commonly used proxy for environmental change and ecophysiology. δ 13 C Ring reconstructions are based on a solid knowledge of isotope fractionations during formation of primary photosynthates (δ 13 C P ), such as sucrose. However, δ 13 C Ring is not merely a record of δ 13 C P . Isotope fractionation processes, which are not yet fully understood, modify δ 13 C P during sucrose transport. We traced, how the environmental intra-seasonal δ 13 C P signal changes from leaves to phloem, tree-ring and roots, for 7 year old Pinus sylvestris, using δ 13 C analysis of individual carbohydrates, δ 13 C Ring laser ablation, leaf gas exchange and enzyme activity measurements. The intra-seasonal δ 13 C P dynamics was clearly reflected by δ 13 C Ring , suggesting negligible impact of reserve use on δ 13 C Ring . However, δ 13 C P became increasingly 13 C-enriched during down-stem transport, probably due to post-photosynthetic fractionations such as sink organ catabolism. In contrast, δ 13 C of water-soluble carbohydrates, analysed for the same extracts, did not reflect the same isotope dynamics and fractionations as δ 13 C P , but recorded intra-seasonal δ 13 C P variability. The impact of environmental signals on δ 13 C Ring , and the 0.5 and 1.7‰ depletion in photosynthates compared ring organic matter and tree-ring cellulose, respectively, are useful pieces of information for studies exploiting δ 13 C Ring ., (© 2023 The Authors. Plant, Cell & Environment published by John Wiley & Sons Ltd.)

Eucalyptus: L'Hér. (Myrtaceae) is one of the economically most important and widely cultivated trees for wood crop purposes worldwide. Climatic changes together with the constant need to expand plantations to areas that do not always provide optimal conditions for plant growth highlight the need to assess the impact of abiotic stresses on eucalypt trees. We aimed to unveil the drought effect on the leaf metabolome of commercial clones with differential phenotypic response to this stress. For this, seedlings of 13 clones were grown at well-watered (WW) and water-deficit (WD) conditions and their leaf extracts were subjected to comparative analysis using ultra-high performance liquid chromatography coupled to mass spectrometry (UPLC-MS) and nuclear magnetic resonance spectroscopy (NMR). UPLC-MS and NMR analyses led to the annotation of over 100 molecular features of classes such as cyclitols, phenolics, flavonoids, formylated phloroglucinol compounds (FPCs) and fatty acids. Multivariate data analysis was employed for specimens' classifications and markers identification from both platforms. The results obtained in this work allowed us to classify clones differing in drought tolerance. Classification models were validated using an extra subset of samples. Tolerant plants exposed to water deficit accumulated arginine, gallic acid derivatives, caffeic acid and tannins at higher levels. In contrast, stressed drought-sensitive clones were characterised by a significant reduction in glucose, inositol and shikimic acid levels. These changes in contrasting drought response eucalypt pave ways for differential outcomes of tolerant and susceptible phenotypes. Under optimal growth conditions, all clones were rich in FPCs. These results can be used for early screening of tolerant clones and to improve our understanding of the role of these biomarkers in Eucalyptus tolerance to drought stress., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:Mohamed A. Farag reports financial support was provided by Alexander von Humboldt Foundation. Clarice Noleto-Dias reports financial support was provided by National Council for Scientific and Technological Development., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

After agriculture, wood harvest is the human activity that has most reduced the storage of carbon in vegetation and soils 1,2 . Although felled wood releases carbon to the atmosphere in various steps, the fact that growing trees absorb carbon has led to different carbon-accounting approaches for wood use, producing widely varying estimates of carbon costs. Many approaches give the impression of low, zero or even negative greenhouse gas emissions from wood harvests because, in different ways, they offset carbon losses from new harvests with carbon sequestration from growth of broad forest areas 3,4 . Attributing this sequestration to new harvests is inappropriate because this other forest growth would occur regardless of new harvests and typically results from agricultural abandonment, recovery from previous harvests and climate change itself. Nevertheless some papers count gross emissions annually, which assigns no value to the capacity of newly harvested forests to regrow and approach the carbon stocks of unharvested forests. Here we present results of a new model that uses time discounting to estimate the present and future carbon costs of global wood harvests under different scenarios. We find that forest harvests between 2010 and 2050 will probably have annualized carbon costs of 3.5-4.2 Gt CO 2 e yr -1 , which approach common estimates of annual emissions from land-use change due to agricultural expansion. Our study suggests an underappreciated option to address climate change by reducing these costs., (© 2023. The Author(s).)

Trees are unique in terms of development, sustainability and longevity. Some species have a record lifespan in the living world, reaching several millennia. The aim of this review is to summarize the available data on the genetic and epigenetic mechanisms of longevity in forest trees. In this review, we have focused on the genetic aspects of longevity of a few well-studied forest tree species, such as Quercus robur , Ginkgo biloba , Ficus benghalensis and F. religiosa , Populus , Welwitschia and Dracaena , as well as on interspecific genetic traits associated with plant longevity. A key trait associated with plant longevity is the enhanced immune defense, with the increase in gene families such as RLK , RLP and NLR in Quercus robur, the expansion of the CC-NBS-LRR disease resistance families in Ficus species and the steady expression of R-genes in Ginkgo biloba . A high copy number ratio of the PARP1 family genes involved in DNA repair and defense response was found in Pseudotsuga menziesii , Pinus sylvestris and Malus domestica . An increase in the number of copies of the epigenetic regulators BRU1/TSK/MGO3 (maintenance of meristems and genome integrity) and SDE3 (antiviral protection) was also found in long-lived trees. CHG methylation gradually declines in the DAL 1 gene in Pinus tabuliformis , a conservative age biomarker in conifers, as the age increases. It was shown in Larix kaempferi that grafting, cutting and pruning change the expression of age-related genes and rejuvenate plants. Thus, the main genetic and epigenetic mechanisms of longevity in forest trees were considered, among which there are both general and individual processes.

Leaves are the most important photosynthetic organs in most woody plants, but chloroplasts are also found in organs optimized for other functions. However, the actual photosynthetic efficiency of these chloroplasts is still unclear. We analyzed bark and wood chloroplasts of Fraxinus ornus L. saplings. Optical and spectroscopic methods were applied to stem samples and compared with leaves. A sharp light gradient was detected along the stem radial direction, with blue light mainly absorbed by the outer bark, and far-red-enriched light reaching the underlying xylem and pith. Chlorophylls were evident in the xylem rays and the pith and showed an increasing concentration gradient toward the bark. The stem photosynthetic apparatus showed features typical of acclimation to a low-light environment, such as larger grana stacks, lower chlorophyll a/b and photosystem I/II ratios compared with leaves. Despite likely receiving very few photons, wood chloroplasts were photosynthetically active and fully capable of generating a light-dependent electron transport. Our data provide a comprehensive scenario of the functional features of bark and wood chloroplasts in a woody species and suggest that stem photosynthesis is coherently optimized to the prevailing micro-environmental conditions at the bark and wood level., (© The Author(s) 2023. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permission@oup.com.)

Volatile terpenes serve multiple biological roles including tree resistance against herbivores. The increased frequency and severity of drought stress observed in forests across the globe may hinder trees from producing defense-related volatiles in response to biotic stress. To assess how drought-induced physiological stress alters volatile emissions alone and in combination with a biotic challenge, we monitored pre-dawn water potential, gas-exchange, needle terpene concentrations and terpene volatile emissions of ponderosa pine (Pinus ponderosa) saplings during three periods of drought and in response to simulated herbivory via methyl jasmonate application. Although 3-, 6- and 7-week drought treatments reduced net photosynthetic rates by 20, 89 and 105%, respectively, the magnitude of volatile fluxes remained generally resistant to drought. Herbivore-induced emissions, however, exhibited threshold-like behavior; saplings were unable to induce emissions above constitutive levels when pre-dawn water potentials were below the approximate zero-assimilation point. By comparing compositional shifts in emissions to needle terpene concentrations, we found evidence that drought effects on constitutive and herbivore-induced volatile flux and composition are primarily via constraints on the de novo fraction, suggesting that reduced photosynthesis during drought limits the carbon substrate available for de novo volatile synthesis. However, results from a subsequent 13CO2 pulse-chase labeling experiment then confirmed that both constitutive (<3% labeled) and herbivore-induced (<8% labeled) de novo emissions from ponderosa pine are synthesized predominantly from older carbon sources with little contribution from new photosynthates. Taken together, we provide evidence that in ponderosa pine, drought does not constrain herbivore-induced de novo emissions through substrate limitation via reduced photosynthesis, but rather through more sophisticated molecular and/or biophysical mechanisms that manifest as saplings reach the zero-assimilation point. These results highlight the importance of considering drought severity when assessing impacts on the herbivore-induced response and suggest that drought-altered volatile metabolism constrains induced emissions once a physiological threshold is surpassed., (© The Author(s) 2023. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Many studies have investigated the photoprotective and photosynthetic capacity of plant leaves, but few have simultaneously evaluated the dynamic changes of photoprotective capacity and photosynthetic maturation of leaves at different developmental stages. As a result, the process between the decline of photoprotective substances and the onset of photosynthetic maturation during plant leaf development are still poorly understood, and the relationship between them has not been quantitatively described. In this study, the contents of photoprotective substances, photosynthetic pigment content and photosynthetic capacity of leaves at different developmental stages from young leaves to mature leaves were determined by spatio-temporal replacement in eight dominant tree species in subtropical evergreen broadleaved forests. The correlation analysis found that the data sets of anthocyanins, flavonoids, total phenolics and total antioxidant capacity were mainly distributed on one side of the symmetry axis (y = x), while the data sets of flavonoids, total phenolics and total antioxidant capacity were mainly distributed on both sides of the symmetry axis (y = x). In addition, the content of photoprotective substances in plant leaves was significantly negatively correlated with photosynthetic pigment content and photosynthetic capacity but was significantly positively correlated with dark respiration rate (Rd). When chlorophyll accumulated to ~50% of the final value, the photoprotective substance content and Rd of plant leaves reached the lowest level, and anthocyanins disappeared completely; in contrast, the photosynthetic capacity reached the highest level. Our results suggest that anthocyanins mainly play a light-shielding role in the young leaves of most plants in subtropical forests. In addition, 50% chlorophyll accumulation in most plant leaves was the basis for judging leaf photosynthetic maturity. We also believe that 50% chlorophyll accumulation is a critical period in the transition of plant leaves from high photoprotective capacity (high metabolic capacity, low photosynthetic capacity) to low photoprotective capacity (low metabolic capacity, high photosynthetic capacity)., (© The Author(s) 2023. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Ectomycorrhizas are an intrinsic component of tree nutrition and responses to environmental variations. How epigenetic mechanisms might regulate these mutualistic interactions is unknown. By manipulating the level of expression of the chromatin remodeler DECREASE IN DNA METHYLATION 1 (DDM1) and two demethylases DEMETER-LIKE (DML) in Populus tremula × Populus alba lines, we examined how host DNA methylation modulates multiple parameters of the responses to root colonization with the mutualistic fungus Laccaria bicolor. We compared the ectomycorrhizas formed between transgenic and wild-type (WT) trees and analyzed their methylomes and transcriptomes. The poplar lines displaying lower mycorrhiza formation rate corresponded to hypomethylated overexpressing DML or RNAi-ddm1 lines. We found 86 genes and 288 transposable elements (TEs) differentially methylated between WT and hypomethylated lines (common to both OX-dml and RNAi-ddm1) and 120 genes/1441 TEs in the fungal genome suggesting a host-induced remodeling of the fungal methylome. Hypomethylated poplar lines displayed 205 differentially expressed genes (cis and trans effects) in common with 17 being differentially methylated (cis). Our findings suggest a central role of host and fungal DNA methylation in the ability to form ectomycorrhizas including not only poplar genes involved in root initiation, ethylene and jasmonate-mediated pathways, and immune response but also terpenoid metabolism., (© 2023 The Authors New Phytologist © 2023 New Phytologist Foundation This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.)

Trembling aspen (Populus tremuloides) is arguably the most important deciduous tree species in the Intermountain West of North America. There, as elsewhere in its range, aspen exhibits remarkable genetic variation in observable traits such as morphology and phenology. In contrast to Great Lakes populations, however, relatively little is known about phytochemical variation in western aspen. This survey of phytochemistry in western aspen was undertaken to assess how chemical expression varies among genotypes, cytotypes (diploid vs. triploid), and populations, and in response to development and mammalian browsing. We measured levels of foliar nitrogen, salicinoid phenolic glycosides (SPGs) and condensed tannins (CTs), as those constituents influence organismal interactions and ecosystem processes. Results revealed striking genotypic variation and considerable population variation, but minimal cytotype variation, in phytochemistry of western aspen. Levels of SPGs and nitrogen declined, whereas levels of CTs increased, with tree age. Browsed ramets had much higher levels of SPGs, and lower levels of CTs, than unbrowsed ramets of the same genotype. We then evaluated how composite chemical profiles of western aspen differ from those of Great Lakes aspen (assessed in earlier research). Interestingly, mature western aspen trees maintain much higher levels of SPGs, and lower levels of CTs, than Great Lakes aspen. Phenotypic variation in chemical composition of aspen - a foundation species - in the Intermountain West likely has important consequences for organismal interactions and forest ecosystem dynamics. Moreover, those consequences likely play out over spatial and temporal scales somewhat differently than have been documented for Great Lakes aspen., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Increasing soil carbon and nitrogen storage can help mitigate climate change and sustain soil fertility 1,2 . A large number of biodiversity-manipulation experiments collectively suggest that high plant diversity increases soil carbon and nitrogen stocks 3,4 . It remains debated, however, whether such conclusions hold in natural ecosystems 5-12 . Here we analyse Canada's National Forest Inventory (NFI) database with the help of structural equation modelling (SEM) to explore the relationship between tree diversity and soil carbon and nitrogen accumulation in natural forests. We find that greater tree diversity is associated with higher soil carbon and nitrogen accumulation, validating inferences from biodiversity-manipulation experiments. Specifically, on a decadal scale, increasing species evenness from its minimum to maximum value increases soil carbon and nitrogen in the organic horizon by 30% and 42%, whereas increasing functional diversity enhances soil carbon and nitrogen in the mineral horizon by 32% and 50%, respectively. Our results highlight that conserving and promoting functionally diverse forests could promote soil carbon and nitrogen storage, enhancing both carbon sink capacity and soil nitrogen fertility., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

Phloem loading and sugar distribution are key steps for carbon partitioning in herbaceous and woody species. Although the phloem loading mechanisms in herbs are well studied, less is known for trees. It was shown for saplings of Fagus sylvatica L. and Quercus robur L. that the sucrose concentration in the phloem sap was higher than in the mesophyll cells, which suggests that phloem loading of sucrose involves active steps. However, the question remains whether this also applies for tall trees. To approach this question, tissue-specific sugar and starch contents of small and tall trees of F. sylvatica and Q. robur as well as the sugar concentration in the subcellular compartments of mesophyll cells were examined. Moreover, sucrose uptake transporters (SUTs) were analyzed by heterology expression in yeast and the tissue-specific expressions of SUTs were investigated. Sugar content in leaves of the canopy (11 and 26 m height) was up to 25% higher compared with that of leaves of small trees of F. sylvatica and Q. robur (2 m height). The sucrose concentration in the cytosol of mesophyll cells from tall trees was between 120 and 240 mM and about 4- to 8-fold lower than the sucrose concentration in the phloem sap of saplings. The analyzed SUT sequences of both tree species cluster into three types, similar to SUTs from other plant species. Heterologous expression in yeast confirmed that all analyzed SUTs are functional sucrose transporters. Moreover, all SUTs were expressed in leaves, bark and wood of the canopy and the expression levels in small and tall trees were similar. The results show that the phloem loading in leaves of tall trees of F. sylvatica and Q. robur probably involves active steps, because there is an uphill concentration gradient for sucrose. SUTs may be involved in phloem loading., (© The Author(s) 2022. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permission@oup.com.)

Tropical forests face increasing climate risk 1,2 , yet our ability to predict their response to climate change is limited by poor understanding of their resistance to water stress. Although xylem embolism resistance thresholds (for example, [Formula: see text] 50 ) and hydraulic safety margins (for example, HSM 50 ) are important predictors of drought-induced mortality risk 3-5 , little is known about how these vary across Earth's largest tropical forest. Here, we present a pan-Amazon, fully standardized hydraulic traits dataset and use it to assess regional variation in drought sensitivity and hydraulic trait ability to predict species distributions and long-term forest biomass accumulation. Parameters [Formula: see text] 50 and HSM 50 vary markedly across the Amazon and are related to average long-term rainfall characteristics. Both [Formula: see text] 50 and HSM 50 influence the biogeographical distribution of Amazon tree species. However, HSM 50 was the only significant predictor of observed decadal-scale changes in forest biomass. Old-growth forests with wide HSM 50 are gaining more biomass than are low HSM 50 forests. We propose that this may be associated with a growth-mortality trade-off whereby trees in forests consisting of fast-growing species take greater hydraulic risks and face greater mortality risk. Moreover, in regions of more pronounced climatic change, we find evidence that forests are losing biomass, suggesting that species in these regions may be operating beyond their hydraulic limits. Continued climate change is likely to further reduce HSM 50 in the Amazon 6,7 , with strong implications for the Amazon carbon sink., (© 2023. The Author(s).)

Aqueous extract of Neolamarchia cadamba leaves were used in the synthesis of silver/silver chloride nanoparticles (Ag/AgCl NPs). Further they were separated based on their using step-wise centrifugation approach at 09,000, 12,000, and 15,000 rpm. Thus obtained NPs were characterized for their physicochemical features. NPs showed maximum absorbance at 455 nm, 415 nm, and 402 nm. All the NPs were found to be crystalline in nature with average crystallite size (nm) of 58.31, 23.43, and 09.56. Particle size distribution (nm) of NPs was observed to 435.43, 276.75, and 105.49, Surface charge (-mV) of NPs was observed to be 14.59, 23.90, and 32.17. Ag/AgCl NPs-rpm@15,000 showed antibacterial activity against Escherichia coli, coagulase-negative Staphylococci, and Staphylococcus aureus with zone of inhibition (mm) of 16.65, 13.69, and 14.02 at 50 µg per well, respectively. Ag/AgCl NPs-rpm@15,000 showed excellent catalytic activity in degradation of methyl red, methylene blue, rhodamine-B, and methyl orange dyes in the presence of sodium borohydride under 4, 6, 5, and 4 min with pseudo-first order rate constant (min -1 ) of 0.981 (96.4%), 0.666 (97.1%), 0.905 (98.1%), and 1.032 (96.6%), respectively. Furthermore, Ag/AgCl NPs-rpm@15,000 showed good catalytic efficiency even under different dye combinations. Total combination was degraded under 18 min., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The pathways through which cadmium (Cd) is taken up and loaded into cacao beans (nibs) are yet to be revealed. Previous work suggested that Cd loading into cacao nibs may occur via direct xylem uptake rather than phloem-mediated redistribution from the leaves. A stable isotope ( 108 Cd) pulse-chase experiment was set up to identify the pathways of Cd loading into cacao nibs. The topsoil beneath two mature cacao trees in the field was enriched in 108 Cd via surface irrigation with a spiked solution. The increase in 108 Cd isotopic abundance (IA) in the plant tissues was followed up for 548 days after spiking. The 108 Cd IA in the plant tissues increased from natural abundance (0.89 %) to 7.0 % (tree A) and 10.1 % (tree B) at equilibrium. The tracer was taken up in the plant tissues in the order immature leaves > mature leaves > nibs in both trees, while tracer uptake in flowers and cherelles was less consistent between the trees. Half of the equilibrium 108 Cd IA was reached in the nibs at 191 days after spiking, significantly later than corresponding values for mature (151 days) and immature leaves (117 days). Pod maturation from flower stage takes about 6 months with most Cd entering the nibs at the last stage of development. The rather slow rise in the 108 Cd IA in the nibs compared to the leaves hence suggests that Cd in cacao nibs likely originates from phloem-redistribution from the stem, branches or mature leaves and not from direct root-to-nib transport via the xylem., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Ectomycorrhizal (EcM) fungi play a crucial role in the mineral nitrogen (N) nutrition of their host trees. While it has been proposed that several EcM species also mobilize organic N, studies reporting the EcM ability to degrade N-containing polymers, such as chitin, remain scarce. Here, we assessed the capacity of a representative collection of 16 EcM species to acquire 15 N from 15 N-chitin. In addition, we combined genomics and transcriptomics to identify pathways involved in exogenous chitin degradation between these fungal strains. Boletus edulis, Imleria badia, Suillus luteus, and Hebeloma cylindrosporum efficiently mobilized N from exogenous chitin. EcM genomes primarily contained genes encoding for the direct hydrolysis of chitin. Further, we found a significant relationship between the capacity of EcM fungi to assimilate organic N from chitin and their genomic and transcriptomic potentials for chitin degradation. These findings demonstrate that certain EcM fungal species depolymerize chitin using hydrolytic mechanisms and that endochitinases, but not exochitinases, represent the enzymatic bottleneck of chitin degradation. Finally, this study shows that the degradation of exogenous chitin by EcM fungi might be a key functional trait of nutrient cycling in forests dominated by EcM fungi., (© 2023 The Authors. New Phytologist © 2023 New Phytologist Foundation Some of the authors are U.S. Government employees and their work is in the public domain in the USA.)

Decomposition and fire are major carbon pathways in many ecosystems, yet potential linkages between these processes are poorly understood. We test whether variability in decomposability and flammability across species are related to each other and to key plant functional traits in tropical swamp forests, where habitat degradation is elevating decomposition and fire regimes. Using senesced and fresh leaves of 22 swamp tree species in Singapore, we conducted an in situ decomposition experiment and a laboratory flammability experiment. We analysed 16 leaf physical and biochemical traits as predictors of decomposability and components of flammability: combustibility, ignitability and sustainability. Decomposability and flammability were largely decoupled across species, despite some shared predictive traits such as specific leaf area (SLA). Physical traits predicted that thicker leaves with a smaller SLA and volume decomposed faster, while various cation concentrations predicted flammability components, particularly ignitability. We show that flammability and decomposability of swamp forest leaves are decoupled because flammability is mostly driven by biochemical traits, while decomposition is driven by physical traits. Our approach identifies species that are slow to decompose and burn (e.g. Calophyllum tetrapterum and Xanthophyllum flavescens), which could be planted to mitigate carbon losses in tropical swamp reforestation., (© 2023 The Authors. New Phytologist © 2023 New Phytologist Foundation.)

Although effects of atmospheric nitrogen (N) deposition on forest plants have been widely investigated, N interception and absorption effects by forest canopy should not be neglected. Moreover, how N deposition change the molecular biological process of understory dominant plants, which was easily influenced by canopy interception so as to further change physiological performance, remains poorly understood. To assess the effects of N deposition on forest plants, we investigated the effects of understory (UAN) and canopy N addition (CAN) on the transcriptome and physiological properties of Ardisia quinquegona, a dominant subtropical understory plant species in an evergreen broad-leaved forest in China. We identified a total of 7394 differentially expressed genes (DEGs). Three of these genes were found to be co-upregulated in CAN as compared to control (CK) after 3 and 6 h of N addition treatment, while 133 and 3 genes were respectively found to be co-upregulated and co-downregulated in UAN as compared to CK. In addition, highly expressed genes including GP1 (a gene involved in cell wall biosynthesis) and STP9 (sugar transport protein 9) were detected in CAN, which led to elevated photosynthetic capacity and accumulation of protein and amino acid as well as decrease in glucose, sucrose, and starch contents. On the other hand, genes associated with transport, carbon and N metabolism, redox response, protein phosphorylation, cell integrity, and epigenetic regulation mechanism were affected by UAN, resulting in enhanced photosynthetic capacity and carbohydrates and accumulation of protein and amino acid. In conclusion, our results showed that the CAN compared to UAN treatment had less effects on gene regulation and carbon and N metabolism. Canopy interception of N should be considered through CAN treatment to simulate N deposition in nature., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Epiphytic and rupicolous plants inhabit environments with limited water resources. Such plants commonly use Crassulacean Acid Metabolism (CAM), a photosynthetic pathway that accumulates organic acids in cell vacuoles at night, so reducing their leaf water potential and favouring water absorption. Foliar water uptake (FWU) aids plant survival during drought events in environments with high water deficits. We hypothesized that FWU represents a strategy employed by epiphytic and rupicolous orchids for water acquisition and that CAM will favour increased water absorption. We examined 6 epiphyte, 4 terrestrial and 6 rupicolous orchids that use C3 (n = 9) or CAM (n = 7) pathways. Five individuals per species were used to evaluate FWU, structural characteristics and leaf water balance. Rupicolous species with C3 metabolism had higher FWU than other species. FWU (C max and k) could be related to succulence, SLM and leaf RWC. The results indicated that high orchid leaf densities favoured FWU, as area available for water storage increases with leaf density. Structural characteristics linked to water storage (e.g. high RWC, succulence), on the other hand, could limit leaf water absorption by favouring high internal leaf water potentials. Epiphytic, rupicolous and terrestrial orchids showed FWU. Rupicolous species had high levels of FWU, probably through absorption from mist. However, succulence in plants with CAM appears to mitigate FWU., (© 2022 German Society for Plant Sciences, Royal Botanical Society of the Netherlands.)

The globally important carbon sink of intact, old-growth tropical humid forests is declining because of climate change, deforestation and degradation from fire and logging 1-3 . Recovering tropical secondary and degraded forests now cover about 10% of the tropical forest area 4 , but how much carbon they accumulate remains uncertain. Here we quantify the aboveground carbon (AGC) sink of recovering forests across three main continuous tropical humid regions: the Amazon, Borneo and Central Africa 5,6 . On the basis of satellite data products 4,7 , our analysis encompasses the heterogeneous spatial and temporal patterns of growth in degraded and secondary forests, influenced by key environmental and anthropogenic drivers. In the first 20 years of recovery, regrowth rates in Borneo were up to 45% and 58% higher than in Central Africa and the Amazon, respectively. This is due to variables such as temperature, water deficit and disturbance regimes. We find that regrowing degraded and secondary forests accumulated 107 Tg C year -1 (90-130 Tg C year -1 ) between 1984 and 2018, counterbalancing 26% (21-34%) of carbon emissions from humid tropical forest loss during the same period. Protecting old-growth forests is therefore a priority. Furthermore, we estimate that conserving recovering degraded and secondary forests can have a feasible future carbon sink potential of 53 Tg C year -1 (44-62 Tg C year -1 ) across the main tropical regions studied., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

Premise: Climate change may lead to C stress (negative C balance) in trees. Because nonstructural carbohydrates (NSC) are required during metabolic reactivation in the spring, C stress might delay budbreak timing. This effect is expected to be greater in shade-intolerant than in shade-tolerant species, owing to the faster C economy in the shade-intolerant., Methods: We experimentally induced C stress in saplings of six temperate tree species that differed in their light requirements by exposing them to either full light or shade from summer to spring, then recorded the date of first budbreak for the individuals. Because the levels of C reserves that represent effective C stress may differ among species, we estimated the degree of C stress by recording survival during the experiment and measuring whole-sapling NSC concentrations after budbreak., Results: Shade reduced NSC concentrations and increased the sugar fraction in the NSC in all species. In the shade, shade-intolerant species had higher mortality and generally lower NSC concentrations than the shade-tolerant species, indicating a trend for more severe C stress in species with faster C economy. In shade-intolerant species, budbreak started earlier and proceeded faster in full light than in shade, but in shade-tolerant species budbreak was delayed in full light. The effects of the light environments on budbreak were not greater in shade-intolerant than in shade-tolerant species., Conclusions: Our study reveals a correspondence between budbreak responses to light and the light requirements of the species. This finding confirms that C metabolism has a significant role in triggering budbreak and demonstrates that whether C stress accelerates or delays budbreak depends on the species' light requirements., (© 2023 Botanical Society of America.)

The impact of climate change drivers on cultivated plants and pest insects has come into research focus. One of the most significant drivers is atmospheric carbon dioxide, which is converted into primary plant metabolites by photosynthesis. Increased atmospheric CO 2 concentrations therefore affect plant chemistry. The chemical composition of non-volatile and volatile organic compounds of plants is used by insects to locate and identify suitable host plants for feeding and reproduction. We investigated whether elevated CO 2 concentrations in the atmosphere affect the plant-pest interaction in a fruit crop of high economic importance in Europe. Therefore, potted pear trees were cultivated under specified CO 2 conditions in a Free-Air Carbon dioxide Enrichment (FACE) facility at Geisenheim University in Germany for up to 14 weeks, beginning from bud swelling. We compared emitted volatiles from these pear trees cultivated for 7 and 14 weeks under two different CO 2 levels (ambient: ca. 400 ppm and elevated: ca. 450 ppm CO 2 ) and their impact on pest insect behavior. In total, we detected and analyzed 76 VOCs from pear trees. While we did not detect an overall change in VOC compositions, the relative release of single compounds changed in response to CO 2 increase. Differences in VOC release were inconsistent over time (phenology stages) and between study years, indicating interactions with other climate parameters, such as temperature. Even though insect-plant interaction can rely on specific volatile compounds and specific mixtures of compounds, respectively, the changes of VOC patterns in our field study did not impact the host choice behavior of C. pyri females. In olfactometer trials, 64% and 60% of the females preferred the odor of pear trees cultivated under elevated CO 2 for 7 and 14 weeks, respectively, over the odor from pear trees cultivated under ambient CO 2 . In binary-choice oviposition assays, C. pyri females laid most eggs on pears during April 2020; on average, 51.9 (± 51.3) eggs were laid on pears cultivated under eCO 2 and 60.3 (± 48.7) eggs on aCO 2., (© 2023. The Author(s).)

The distribution of dryland trees and their density, cover, size, mass and carbon content are not well known at sub-continental to continental scales 1-14 . This information is important for ecological protection, carbon accounting, climate mitigation and restoration efforts of dryland ecosystems 15-18 . We assessed more than 9.9 billion trees derived from more than 300,000 satellite images, covering semi-arid sub-Saharan Africa north of the Equator. We attributed wood, foliage and root carbon to every tree in the 0-1,000 mm year -1 rainfall zone by coupling field data 19 , machine learning 20-22 , satellite data and high-performance computing. Average carbon stocks of individual trees ranged from 0.54 Mg C ha -1 and 63 kg C tree -1 in the arid zone to 3.7 Mg C ha -1 and 98 kg tree -1 in the sub-humid zone. Overall, we estimated the total carbon for our study area to be 0.84 (±19.8%) Pg C. Comparisons with 14 previous TRENDY numerical simulation studies 23 for our area found that the density and carbon stocks of scattered trees have been underestimated by three models and overestimated by 11 models, respectively. This benchmarking can help understand the carbon cycle and address concerns about land degradation 24-29 . We make available a linked database of wood mass, foliage mass, root mass and carbon stock of each tree for scientists, policymakers, dryland-restoration practitioners and farmers, who can use it to estimate farmland tree carbon stocks from tablets or laptops., (© 2023. This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply.)

Modification of proteins by ubiquitin is a highly regulated process that plays a critical role in eukaryotes, from the construction of signalling platforms to the control of cell division. Aberrations in ubiquitin transfer are associated with many diseases, including cancer and neurodegenerative disorders. The ubiquitin machinery generates a rich code on substrate proteins, spanning from single ubiquitin modifications to polyubiquitin chains with diverse linkage types. Central to this process are the E2 enzymes, which often determine the exact nature of the ubiquitin code. The focus of this mini-review is on the molecular details of how E2 enzymes can initiate and grow ubiquitin chains. In particular, recent developments and biochemical breakthroughs that help explain how the degradative E2 enzymes, Ube2s, Ube2k, and Ube2r, generate complex ubiquitin chains with exquisite specificity will be discussed., (© 2023 The Author(s).)

Stored water in inner tissues influences the plant water economy, which might be particularly relevant for trees facing increasing dry conditions due to climate change. We studied the water storage in the inner bark and the sapwood of Araucaria araucana (Molina) K. Koch. This species has an extremely thick inner bark and thus it can be used as a model system to assess the impact of internal water storage on plant water balance. Specifically, we analyzed the water circulation pathways in and out of the elastic water storages by using simultaneously frequency domain moisture sensors and dendrometers inserted in the inner bark and in the sapwood, and sap flow determinations during the dry season. The daily patterns of water content and expansion and contraction of the stem tissues were similar to the sap flow pattern. The whole-stem water content and diameter increased in the morning and decreased in the afternoon, contrary to the typical pattern observed in most tree species. An osmotic gradient favoring the water influx from sapwood to inner bark was observed in the morning. There were no lags in the onset of sap flow between different stem heights at the time that recharge of reservoirs occurred. Sap flow at 6 m height was higher than basal sap flow in the afternoon, when the sapwood water content started to decline followed by the water content of the inner bark. Inner bark and sapwood contributed 5-11% to total daily transpiration, allowing the maintenance of high water potentials in the dry season. Our results suggest that the stored water in the stems, the atypical dynamic of recharge and discharge of water from reservoirs and the high tissue capacitance may make an important contribution to the survival of A. araucana during drought periods by maintaining the water balance., (© The Author(s) 2022. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permission@oup.com.)

Megaherbivores have pervasive ecological effects. In African rainforests, elephants can increase aboveground carbon, though the mechanisms are unclear. Here, we combine a large unpublished dataset of forest elephant feeding with published browsing preferences totaling nearly 200,000 records covering >800 plant species and with nutritional data for 145 species. Elephants increase carbon stocks by: 1) promoting high wood density trees via preferential browsing on leaves from low wood density species, which are more palatable and digestible; and 2) dispersing seeds of trees that are relatively large and have the highest average wood density among tree guilds based on dispersal mode. Loss of forest elephants could cause an increase in abundance of fast-growing low wood density trees and a 6% to 9% decline in aboveground carbon stocks due to regeneration failure of elephant-dispersed trees. These results demonstrate the importance of megaherbivores for maintaining diverse, high-carbon tropical forests. Successful elephant conservation will contribute to climate mitigation at a globally-relevant scale.

The iron ore tailings released into the Rio Doce basin after the Fundão dam collapse (Brazil), suppressed a large extent of local vegetation. The use of native species and appropriate fertilization techniques, with less economic and environmental impact, must be considered in the process for the restoration of affected areas by the tailings. For this purpose, six native tree species, pioneer (Anadenanthera colubrina, Bixa orellana, and Peltophorum dubium) and secondary (Cedrela fissilis, Handroanthus impetiginosus, and Handroanthus serratifolius), were selected. We used different conditions of fertilization: (1) inorganic fertilization, (2) inoculation with arbuscular mycorrhizal fungi and plant growth-promoting rhizobacteria, (3) combined treatment (fertilizer + inoculum), to evaluate leaf nutrient concentrations, photosynthetic capacity [chlorophyll index, maximum quantum efficiency of photosystem II (Fv/Fm) and gas exchange variables], and oxidative metabolism (H 2 O 2 , MDA, and antioxidant enzymes). Inoculation resulted in higher concentrations of foliar nitrogen, especially in pioneer species. In all treatments, the secondary species exhibited iron values considered phytotoxic, but showed reduced photosynthetic capacity only when inoculated. The highest concentrations of MDA were observed in inoculated plants of both successional groups. The antioxidant system proved to be effective in preventing oxidative damage for most of the species. These results showed that the use of inoculum can be considered an ecological alternative to inorganic additives in the area affected by iron ore tailings. Despite presenting different photosynthetic and antioxidant strategies, the evaluated species demonstrated potential for use in tailings revegetation projects., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Acrylamide (ACR), organic compound, has been widely used owing to its broad spectrum of chemical and industrial applications. This study aims at evaluating the response of the antioxidant defense system, fatty acid composition and histopathological aspect in the respiratory trees of Holothuria forskali against ACR exposure under laboratory conditions. Holothuries were exposed to 5, 10, and 20 mg L -1 ACR concentrations for 5 days. A significant increase in n-6 polyunsaturated fatty acids levels especially the arachidonic acid (ARA, C20:4n-6) and its precursor linoleic acid (LA, C18:2n-6) in ACR-treated organisms. Regarding the n-3 levels, eicosapentaenoic acid (EPA, C20:5n-3) levels were increased in treated groups despite an acute decrease in docosahexaenoic acid (DHA, C22:6n-3) levels was observed. Our results showed a significant increase in hydrogen peroxide, malondialdehyde, protein carbonyl, and metallothionein levels along with an alteration of the antioxidants status in all treated sea cucumbers. The exposure to ACR prompted the inhibition of Acetylcholinesterase activity in a concentration-dependent manner. The histopathological aspect was marked especially with the infiltration of coelomic cells which confirms our biochemical findings. Our study provided novel insights to create a link between redox status and fatty acid composition disruptions to better understand ACR-triggered toxicity., (© 2022 Wiley Periodicals LLC.)

Nitrogen-fixing Nepalese alder ( Alnus nepalensis D. Don.), a pioneer species and nurse tree species, forms pure stands, and sometimes occurs in mixed stands in areas affected by landslides. The objective of this study was to understand the influence of A. nepalensis on carbon stock in white oak ( Quercus leucotrichophora A. Camus) forests. We investigated the differences in vegetation biomass carbon (tree, sapling, seedling, shrub and herbs, and forest floor mass), soil organic carbon stock, and sequestration rates in five naturally occurring oak mixed alder (OMA) forest stands and five naturally occurring oak without alder (OWA) forest stands along the basal area gradient in order to investigate the role of A. nepalensis on ecosystem carbon stock. The total basal area ranged from 61.20 to 89.51 m 2 ha -1 in the OMA stands and from 38.02 to 53.54 m 2 ha -1 in the OWA stands. The total tree density of the OMA stands (1120 to 1330 trees ha-1) was higher than that of the OWA stands (950 to 1230 trees ha -1 ). The total ecosystem carbon stock in the OMA stands was significantly (P<0.05) higher than that in the OWA stands, ranging from 485.3 to 635.6 Mg C ha -1 in the former and from 378.8 to 472 Mg C ha -1 in the latter. Soil was the second largest carbon pool in all the studied stands, with the values ranging from 238.1 to 254.1 Mg C ha -1 in the OMA and 185.5 to 215.8 Mg C ha -1 in the OWA stands. The soil organic carbon (SOC) stock was 1.19 to 1.28 times higher in the OMA than in the OWA stands. Of the total ecosystem carbon stock in different OMA stands, A. nepalensis stored 16.2 to 38.8%. Annual carbon sequestration rates (6.6 to 9.5 Mg C ha -1 yr -1 ) in the OMA stands were significantly (P<0.05) higher than in the OWA (2.5 to 5.4 Mg C ha -1 yr -1 ) stands. Among all the species and across the stands, the greatest carbon sequestration was exhibited by A. nepalensis (3.4 to 5.3 Mg C ha -1 yr -1 ). The present results show the role of A. nepalensis in ecosystem carbon stock and sequestration rates. Significantly higher rates of carbon sequestration by oak in OMA stands than OWA stands clearly indicate the facilitative role of co-occurring nitrogen-fixing A. nepalensis . The results imply that Q. leucotrichophora mixed with a A. nepalensis plantation may be a good option for enhancing ecosystem carbon stock, carbon sequestration, and habitat restoration in the central Himalaya.

Fasciclin-like arabinogalactan proteins (FLAs) are a class of highly glycosylated glycoproteins that perform crucial functions in plant growth and development. This study was carried out to further explore their roles in pollen tube growth. The results showed that seven members (CoFLA1/2/3/4/7/8/17) of the CoFLAs family were identified by sequence characteristics, and they all possessed the fasciclin 1 (FAS1) domain and H1 and H2 conserved domains. They were all located on the plasma membranes of tobacco epidermal cells, and the GPI-anchor sequences of CoFLA1/2/3/4 determined the membrane localization. In flower tissues, CoFLA2 and CoFLA8 were not expressed in the pollen tube but were expressed in the unpollinated style and ovary; the others were all expressed in the pollen tube. In the pollination-compatible style and ovary, they exhibited different expression patterns. Furthermore, all CoFLAs promoted pollen germination in vitro, while only CoFLA7 significantly promoted pollen tube elongation, and the expression of CoFLA1/3/4/7/17 in pollen tubes was regulated by CoFLA proteins. The ABA and ABA synthetic inhibitor (sodium tungstate, ST) both inhibited pollen tube elongation; however, only ST downregulated the expression of CoFLA1/7/17 and upregulated the expression of CoFLA4. Taken together, these results demonstrate that CoFLAs may be significant in pollen tube growth in C. oleifera and that some CoFLAs may participate in the regulation of ABA signaling., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Forest productivity is generally limited by nutrient scarcity. This study aims to reveal seasonal interactions among leaf carbon (C), nitrogen (N) fractions and tree growth driven by nutrient addition in a subtropical forest. Here, a field nutrient addition experiment was conducted with six treatments, namely, +N 5 (5 g N m -2 yr -1 ), +N 10 (10 g N m -2 yr -1 ), +P 5 (5 g P m -2 yr -1 ), +N 5 + P 5 , +N 10 + P 5 , and control (N 0 + P 0 ). C fractions (structural and non-structural carbohydrates) and N fractions (soluble N, nucleic N and protein N) in needles as well as tree growth indicated by basal area increment (BAI) were measured in growing and dormant seasons. Total N and protein N in old needles were significantly increased by P addition, while no significant differences of non-structural carbohydrates in young (<1-year old) and old needles (>1-year old) were detected among the treatments in both seasons. N and P addition increased the structural carbohydrates of old needles in dormant season. P addition decreased and increased tree growth in growing and dormant seasons, respectively. The variation of BAI was explained 18.3 % by total N and 17.8 % by protein N in growing season, and was explained 33.9 % by total N and 34.2 % by protein N in dormant season. Our study suggested that the P addition effect on Chinese fir growth mostly depends on needle N fractions. This study highlights tree seasonal growth driven by nutrient alteration might be characterized by leaf N fractions rather than C fractions in subtropical forests., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Pongamia pinnata (L.) Pierre (Pongamia) is a tree native to Southeast Asia. Recently, interest in Pongamia focused on its potential as a biofuel source as its seeds contain around 40% oil. However, Pongamia has multiple applications beyond biofuel production. It is a legume, can form symbiotic associations with mycorrhizal fungi, has been shown to be tolerant to drought, salinity, and heavy metals in soil, and has potential to mitigate climate change. Additionally, Pongamia oil has medicinal properties, can be used as biopesticide, insect repellent, to produce soap, and as a source of edible grade vegetable oil. The seed cake can be used as a source of bioenergy, food and feed protein, and organic fertiliser, and the flowers are a good source of pollen and nectar. Pongamia can also bring socio-economic benefits as its ability to restore degraded and contaminated land provides opportunities for local communities through novel valorisation pathways. These multiple applications have potential to form part of a circular bioeconomy in line with sustainable development goals. Although research on the multiple applications of Pongamia has grown considerably, knowledge gaps remain and these need to be addressed so that the full potential of Pongamia can be achieved. Further understanding of the mechanisms underlying its resilience to abiotic stresses, phytoremediation potential and biotic interactions should be a priority, and co-ordinated breeding efforts will be key. Here, we critically review the available literature on Pongamia and highlight gaps in knowledge in which future research should focus on to ensure that the full potential of this versatile tree can be achieved. We conclude that Pongamia can potentially form part of a circular bioeconomy and that harnessing the multiple applications of Pongamia in a holistic manner, with collaboration among key stakeholders, is crucial for the successful application of its benefits far beyond biofuel production., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests. Benjamin Warr reports a relationship with Phyla Earth that includes: board membership. M.V.R. Prasad reports a relationship with Phyla Earth that includes: consulting or advisory., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Glyphosate excessive use is reported in Brazilian citrus orchards, whereas there is speculation about its consequences and the published studies are contradictory and inconclusive. This study aimed to describe the possible harmful effects by simulating glyphosate drift directly to the leaves of ∼4-yr-old citrus plants. As major results, glyphosate doses >360 g ae ha -1 increased the shikimate accumulation in leaves (up to 2.3-times above control), which was increased after a second glyphosate application (up to 3.5-times above control), even after a 240-d interval. Interestingly, shikimate accumulation was occasionally related to a dose-response of the herbicide at specific times; however, the doses had their accumulation peak on determined dates. These accumulations were directly correlated to reduced net photosynthesis even months after the glyphosate sprays. Quantum productivity based on electron transport through the photosystem II and apparent electron transport reductions up to 17% were also observed during the entire experiment course. Similarly, quantum productivity based on CO 2 assimilation of glyphosate sprayed leaves decreased up to four times compared to the control after the second application. Glyphosate doses >360 g ae ha -1 increased stomatal conductance and transpiration as the carboxylation efficiency decreased, evidencing a carbon drainage in the Calvin-Benson cycle. These metabolic and physiological disturbances suggest possible photooxidative damage and an increase in photorespiration, which may be a mitigation strategy by the citrus plants to glyphosate effects, by the cost of reducing the citrus fruit yield (up to 57%). It is concluded that glyphosate phytotoxicity damages citrus plants over time due to chronic disturbances in the shikimate pathway and photosynthesis, even when there are no symptoms. This study is the first report to demonstrate how glyphosate damages citrus trees beyond the shikimate pathway., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Rodrigo Martinelli reports financial support was provided by Coordination of Higher Education Personnel Improvement. Fernando Alves de Azevedo reports financial support was provided by State of Sao Paulo Research Foundation. Dirceu de Mattos Jr reports financial support was provided by State of Sao Paulo Research Foundation. Fernando Alves de Azevedo reports financial support was provided by National Council for Scientific and Technological Development., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Recent observations suggest that the large carbon sink in mature and recovering forests may be strongly limited by nitrogen 1-3 . Nitrogen-fixing trees (fixers) in symbiosis with bacteria provide the main natural source of new nitrogen to tropical forests 3,4 . However, abundances of fixers are tightly constrained 5-7 , highlighting the fundamental unanswered question of what limits new nitrogen entering tropical ecosystems. Here we examine whether herbivory by animals is responsible for limiting symbiotic nitrogen fixation in tropical forests. We evaluate whether nitrogen-fixing trees experience more herbivory than other trees, whether herbivory carries a substantial carbon cost, and whether high herbivory is a result of herbivores targeting the nitrogen-rich leaves of fixers 8,9 . We analysed 1,626 leaves from 350 seedlings of 43 tropical tree species in Panama and found that: (1) although herbivory reduces the growth and survival of all seedlings, nitrogen-fixing trees undergo 26% more herbivory than non-fixers; (2) fixers have 34% higher carbon opportunity costs owing to herbivory than non-fixers, exceeding the metabolic cost of fixing nitrogen; and (3) the high herbivory of fixers is not driven by high leaf nitrogen. Our findings reveal that herbivory may be sufficient to limit tropical symbiotic nitrogen fixation and could constrain its role in alleviating nitrogen limitation on the tropical carbon sink., (© 2022. The Author(s), under exclusive licence to Springer Nature Limited.)

Mining activity has degraded large extensions of soil and its waste is composed of metals, anthropogenic chemicals, and sterile rocks. The use of native species in the recovery of polluted soils improves the conditions for the emergence of other species, tending to a process of ecosystem restoration. The objective of this study was to evaluate the bioaccumulation of metal(loid)s in four species of native plants and the effect of their distribution and bioavailability in soil with waste from an abandoned gold mine. Soil samples were taken from two sites in La Planta, San Juan, Argentina: Site 1 and Site 2 (mining waste and reference soil, respectively). In Site 1, vegetative organ samples were taken from Larrea cuneifolia, Bulnesia retama, Plectrocarpa tetracantha, and Prosopis flexuosa. The concentration of metal(loid)s in soil from Site 1 were Zn > As > Cu > Cd, reaching values of 7123, 6516, 240 and 76 mg kg -1 , respectively. The contamination indices were among the highest categories of contamination for all four metal(loid)s. The spatial interpolation analysis showed the effect of the vegetation as the lowest concentration of metal(loid)s were found in rhizospheric soil. The maximum concentrations of As, Cu, Cd and Zn found in vegetative organs were 371, 461, 28, and 1331 mg kg -1 , respectively. L. cuneifolia and B. retama presented high concentrations of Cu and Zn. The most concentrated metal(loid)s in P. tetracantha and P. flexuosa were Zn, As and Cu. Cd was the least concentrated metal in all four species. The values of BAF and TF were greater than one for all four species. In conclusion, the different phytoextraction capacities and the adaptations to arid environments of these four species are an advantage for future phytoremediation strategies. Their application contributes to the ecological restoration and risk reduction, allowing the recovery of ecosystem services., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Drought and waterlogging impede tree growth and may even lead to tree death. Oaks, an emblematic group of tree species, have evolved a range of adaptations to cope with these constraints. The two most widely distributed European species, pedunculate (PO; Quercus robur L.) and sessile oak (SO; Quercus petraea Matt. Lieb), have overlapping ranges, but their respective distribution are highly constrained by local soil conditions. These contrasting ecological preferences between two closely related and frequently hybridizing species constitute a powerful model to explore the functional bases of the adaptive responses in oak. We exposed oak seedlings to waterlogging and drought, conditions typically encountered by the two species in their respective habitats, and studied changes in gene expression in roots using RNA-seq. We identified genes that change in expression between treatments differentially depending on species. These "species × environment"-responsive genes revealed adaptive molecular strategies involving adventitious and lateral root formation, aerenchyma formation in PO, and osmoregulation and ABA regulation in SO. With this experimental design, we also identified genes with different expression between species independently of water conditions imposed. Surprisingly, this category included genes with functions consistent with a role in intrinsic reproductive barriers. Finally, we compared our findings with those for a genome scan of species divergence and found that the expressional candidate genes included numerous highly differentiated genetic markers between the two species. By combining transcriptomic analysis, gene annotation, pathway analyses, as well as genome scan for genetic differentiation among species, we were able to highlight loci likely involved in adaptation of the two species to their respective ecological niches., (© American Society of Plant Biologists 2022. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Wood is an abundant and renewable feedstock for the production of pulp, fuels, and biobased materials. However, wood is recalcitrant toward deconstruction into cellulose and simple sugars, mainly because of the presence of lignin, an aromatic polymer that shields cell-wall polysaccharides. Hence, numerous research efforts have focused on engineering lignin amount and composition to improve wood processability. Here, we focus on results that have been obtained by engineering the lignin biosynthesis and branching pathways in forest trees to reduce cell-wall recalcitrance, including the introduction of exotic lignin monomers. In addition, we draw general conclusions from over 20 years of field trial research with trees engineered to produce less or altered lignin. We discuss possible causes and solutions for the yield penalty that is often associated with lignin engineering in trees. Finally, we discuss how conventional and new breeding strategies can be combined to develop elite clones with desired lignin properties. We conclude this review with priorities for the development of commercially relevant lignin-engineered trees., (Copyright © 2022 The Author(s). Published by Elsevier Inc. All rights reserved.)

Soil and water in Egypt have become contaminated with multiple pollutants. These contaminants arise from diverse sources, including misuse of fertilizers, industrial effluent discharged into irrigation water, discharge of wastewater in rural areas, and mining activities discharging wet and dry atmospheric deposits and heavy metal contamination. The pollutants can directly affect the quality of air, water, and food and have an adverse effect on human health. About 33% of the cultivated lands in Egypt are salinized due to extreme conditions like high temperatures and aridity. The presence of elevated salt levels in the soil leads to grave consequences for seed germination, plant biochemical processes, development, and reproduction, all of which result in the output of reactive oxygen species and eventually plant death. Despite the possibility of thermal, chemical, or a combination of the two to remediate contaminated soils, their applications are complicated and costly. Some plants, called hyperaccumulators, exhibit the potential to clean up pollutants safely from the soil and water at a low cost. All the technologies used in soil decontamination are called phytoremediation. Some physiological (e.g., phytoextraction, phytostabilization, phytotransformation, rhizofiltration, phytostimulation, phytovolatilization, phytodegradation, and phytodesalination) and molecular parameters (e.g., genes, peptides, and proteins) are involved in heavy metals accumulation of these plants. Although trees are not classified as hyperaccumulators, they have recently proved higher phytoremediation potential than herbaceous plants due to their deeper root system and greater biomass growth. Indeed, this review sheds the light on the application of trees for the phytoremediation of salts and heavy metals in Egypt., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

In the apple tree, insufficient flower bud production is an intractable challenge, and very little information is available in this field due to the fact that research done in this sector is very rare owing to its extended life cycles and low rate of genetic transformation. Here we display novel changes and events in spur buds of Malus × domestica trees after they were exposed to salicylic acid (SA) treatment during the flower induction period. We found a significant increase in morphological indexes, followed by a wider and well-defined shoot apical meristem in SA-treated spur buds. Additionally, we observed increased oxidative stress markers and enzymatic antioxidants in control-treated buds during the flower induction period, while non-enzymatic antioxidants were recorded higher in SA-treated buds. Maximum flowering was observed in SA-treated trees in the next year. Furthermore, ultra-high-performance liquid chromatography (u-HPLC) analysis displays that SA treatment enhances SA and indole acetic acid (IAA), while having an antagonistic effect on gibberellin (GA). At different time points, transcriptome analysis was conducted to analyze the transcriptional response of CK and SA treated buds. Pathway enrichment was detected in differentially expressed genes (DEGs). Agamous (AGL) and SQUAMOSA-promoter binding protein-like (SPL) family related flowering genes display a positive signal for the increased flowering in SA-treated trees, which confirms our findings. As far as we know, there is no report available on the response of spur buds to SA treatment during the flower induction period. This data provides a new theoretical reference for the management of apple tree flowering and also provides an essential basis for future analysis of the regulation and control of flowering in M. domestica., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Chlorophyll breakdown is observed during senescence. The first step in chlorophyll breakdown is the removal of central Mg by Mg-dechelatase. This reaction is the rate-limiting step in the chlorophyll breakdown pathway. We evaluated the effect of induced chlorophyll breakdown on abscission through the removal of Mg by Mg-dechelatase. Poplar transformants carrying the dexamethasone-inducible Mg-dechelatase gene were prepared using the Arabidopsis Stay-Green1 cDNA. When leaves were treated with dexamethasone, chlorophyll was degraded, photosynthetic capacity was reduced, and an abscission zone was formed, resulting in leaf abscission. In addition, ethylene, which plays an important role during senescence, was produced in this process. Thus, chlorophyll breakdown induces the phenotype in the same way as commonly observed during leaf senescence. This study suggests a physiological role of chlorophyll breakdown in the leaf abscission of deciduous trees. Furthermore, this study shows that the dexamethasone-inducible gene expression system is an available option for deciduous tree studies., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Throughfall deposition is an important pathway via which particles, aerosols and gases can move from the atmosphere to the forest floor, which can greatly impact forest biodiversity and functioning. Although throughfall deposition biochemistry has been well studied in forest ecosystems, less is known about how throughfall deposition is modified by tree species diversity. To disentangle the effects of tree species identity and diversity on throughfall deposition, we installed rain gauges in a 10-year-old tree diversity experiment. With these rain gauges, we monitored throughfall biweekly, and performed chemical analyses monthly for all the major ions (Na + , Cl - , SO 4 2- -S, K + , Ca 2+ , Mg 2+ , PO 4 3- -P, NO 3 - -N and NH 4 + -N), for a period of one year. Based on these data, we analysed species identity (i.e. whether throughfall deposition depended on the tree species present in the overstorey), and diversity effects (i.e. whether throughfall deposition depended on tree species richness). We confirmed species identity effects on throughfall deposition. Presence of pine led to higher throughfall deposition of inorganic nitrogen, and lower amounts of phosphorus, calcium and magnesium reaching the forest floor. Additionally, species characteristics and stand structural characteristics, i.e. basal area and canopy cover, emerged as key factors driving throughfall deposition of sodium, chloride, nitrate, sulphate and potassium. Tree species diversity effects on throughfall deposition were also present, mostly via increased basal area and canopy cover, leading to increased throughfall deposition of inorganic nitrogen, sulphate, chloride, sodium and potassium. Our findings thus suggest that tree species diversity enhances throughfall deposition of most ions that we analysed, potentially increasing nutrient availability for below-canopy plant communities. Given that inorganic nitrogen and sulphur are major atmospheric pollutants, increased deposition in mixed plots might affect ecosystem functioning. Further research will be needed to determine the extent of this impact., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Leaves of Mediterranean evergreen tree species experience a reduction in net CO2 assimilation (AN) and mesophyll conductance to CO2 (gm) during aging and senescence, which would be influenced by changes in leaf anatomical traits at cell level. Anatomical modifications can be accompanied by the dismantling of photosynthetic apparatus associated to leaf senescence, manifested through changes at the biochemical level (i.e., lower nitrogen investment in photosynthetic machinery). However, the role of changes in leaf anatomy at cell level and nitrogen content in gm and AN decline experienced by old non-senescent leaves of evergreen trees with long leaf lifespan is far from being elucidated. We evaluated age-dependent changes in morphological, anatomical, chemical and photosynthetic traits in Quercus ilex subsp. rotundifolia Lam., an evergreen oak with high leaf longevity. All photosynthetic traits decreased with increasing leaf age. The relative change in cell wall thickness (Tcw) was less than in chloroplast surface area exposed to intercellular air space (Sc/S), and Sc/S was a key anatomical trait explaining variations in gm and AN among different age classes. The reduction of Sc/S was related to ultrastructural changes in chloroplasts associated to leaf aging, with a concomitant reduction in cytoplasmic nitrogen. Changes in leaf anatomy and biochemistry were responsible for the age-dependent modifications in gm and AN. These findings revealed a gradual physiological deterioration related to the dismantling of the photosynthetic apparatus in older leaves of Q. ilex subsp. rotundifolia., (© The Author(s) 2022. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Drought is an abiotic stress that limits plant growth and productivity, and the development of trees with improved drought tolerance is expected to expand potential plantation areas and to promote sustainable development. Previously we reported that transgenic poplars (Populus tremula × P. tremuloides, T89) harboring the stress-responsive galactinol synthase gene, AtGolS2, derived from Arabidopsis thaliana were developed and showed improved drought stress tolerance in laboratory conditions. Herein we report a field trial evaluation of the AtGolS2-transgenic poplars. The rainfall-restricted treatments on the poplars started in late May 2020, 18 months after transplanting to the field, and were performed for 100 days. During these treatments, the leaf injury levels were observed by measuring photosynthetic quantum yields twice a week. Observed leaf injury levels varied in response to soil moisture fluctuation and showed a large difference between transgenic and non-transgenic poplars during the last month. Comparison of the leaf injury levels against three stress classes clustered by the machine learning approach revealed that the transgenic poplars exhibited significant alleviation of leaf injuries in the most severe stress class. The transgenes and transcript levels were stable in the transgenic poplars cultivated in the field conditions. These results indicated that the overexpression of AtGolS2 significantly improved the drought stress tolerance of transgenic poplars not only in the laboratory but also in the field. In future studies, molecular breeding using AtGolS2 will be an effective method for developing practical drought-tolerant forest trees., (© 2022. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Citrus is a major fruit crop cultivated on a global scale. Citrus trees are long lived perennials with a large canopy. Understanding the genetic control of tree architecture could provide tools for breeding and selection of citrus cultivars suitable for high density planting with improved light exposure. Tree architecture is modulated by the TILLER ANGLE CONTROL 1 (TAC1) gene which plays an important role in the regulation of the shoot angle. Herein, we used CRISPR/Cas9 technology to knockout the CsTAC1 gene for the biochemical and molecular analysis of its function. Nine transgenic lines were obtained, and five edited plants were confirmed based on T7EI mismatch detection assay and Sanger sequencing. The transgenic citrus lines exhibited pleiotropic phenotypes, including differences in branch angle and stem growth. Additionally, silencing CsTAC1 led to enhanced CsLAZY1 transcript levels in the tested lines. Analysis of the phytohormonal profile revealed that TAC1-edited plants exhibited lower auxin contents and increased cytokinin levels in the leaves compared to the wild-type plants. The GA 7 gibberellin level was enhanced in most of the edited lines. Collectively, TAC1 affects branch angle in association with hormone signals in citrus., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Over the last half century in the United States, the per-hectare volume of wood in trees has increased, but it is not clear whether this increase has been driven by forest management, forest recovery from past land uses, such as agriculture, or other environmental factors such as elevated carbon dioxide, nitrogen deposition, or climate change. This paper uses empirical analysis to estimate the effect of elevated carbon dioxide on aboveground wood volume in temperate forests of the United States. To accomplish this, we employ matching techniques that allow us to disentangle the effects of elevated carbon dioxide from other environmental factors affecting wood volume and to estimate the effects separately for planted and natural stands. We show that elevated carbon dioxide has had a strong and consistently positive effect on wood volume while other environmental factors yielded a mix of both positive and negative effects. This study, by enabling a better understanding of how elevated carbon dioxide and other anthropogenic factors are influencing forest stocks, can help policymakers and other stakeholders better account for the role of forests in Nationally Determined Contributions and global mitigation pathways to achieve a 1.5 degree Celsius target., (© 2022. This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply.)

Plant litter decomposition is a crucial pathway for carbon (C) and nutrient cycling, and controls the net primary productivity in ecosystems worldwide. However, little is known about how multi-type litter (leaf and different diameter fine roots) decomposition rates and nutrient release change at the community level following whole-tree harvesting (WTH). In the present study, we followed decomposition of leaf and different diameter fine root (∅ < 0.5 mm, 0.5-1 mm, 1-2 mm) litters at plot level over 2 years in a secondary forest in the Qinling Mountains after 5 years of five different thinning treatments (0%, 15%, 30%, 45%, and 60%). Our results demonstrated that WTH had no effects on leaf and different diameter fine root litter decomposition at the plot level. Leaves had significantly higher decomposition rate than different diameter fine roots. There were significant positive correlations between decomposition rate of different diameter fine roots, but not related to leaf litter decomposition rate. WTH did not affect the nutrient release of leaf and different diameter fine root litters at the plot level. The nitrogen (N), phosphorous (P) and potassium (K) mass remaining in leaf litters were significantly higher than different diameter fine roots after 2 years decomposition, while different diameter fine roots had higher C mass remaining. Leaf and fine root litter decomposition rates were mainly influenced by stand and litter quality attributes. Nutrient release of leaf and fine root N, P and K were mainly predicted by litter quality characteristics, while there were no consistent driving factors for C release. Our results suggested that WTH had no effects on multi-type litter decomposition and nutrient release at plot level after 5 years of recovery. Moreover, leaf litters had excellent N, P and K nutrient preservation mechanisms, and C conservation in fine root litters., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Monoterpenes (C 10 H 16 ) are emitted in large quantities by vegetation to the atmosphere (>100 TgC year -1 ), where they readily react with hydroxyl radicals and ozone to form new particles and, hence, clouds, affecting the Earth's radiative budget and, thereby, climate change 1-3 . Although most monoterpenes exist in two chiral mirror-image forms termed enantiomers, these (+) and (-) forms are rarely distinguished in measurement or modelling studies 4-6 . Therefore, the individual formation pathways of monoterpene enantiomers in plants and their ecological functions are poorly understood. Here we present enantiomerically separated atmospheric monoterpene and isoprene data from an enclosed tropical rainforest ecosystem in the absence of ultraviolet light and atmospheric oxidation chemistry, during a four-month controlled drought and rewetting experiment 7 . Surprisingly, the emitted enantiomers showed distinct diel emission peaks, which responded differently to progressive drying. Isotopic labelling established that vegetation emitted mainly de novo-synthesized (-)-α-pinene, whereas (+)-α-pinene was emitted from storage pools. As drought progressed, the source of (-)-α-pinene emissions shifted to storage pools, favouring cloud formation. Pre-drought mixing ratios of both α-pinene enantiomers correlated better with other monoterpenes than with each other, indicating different enzymatic controls. These results show that enantiomeric distribution is key to understanding the underlying processes driving monoterpene emissions from forest ecosystems and predicting atmospheric feedbacks in response to climate change., (© 2022. The Author(s).)