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The microbial community within the root system, the rhizosphere closely connected to the root, and their symbiotic relationship with the host are increasingly seen as possible drivers of natural pathogen resistance. Resistant cultivars have the most effective strategy in controlling the Chinese wheat yellow mosaic disease, but the roles of the root and rhizosphere microbial interactions among different taxonomic levels of resistant cultivars are still unknown. Thus, we aimed to investigate whether these microbial community composition and network characteristics are related to disease resistance and to analyze the belowground plant-associated microflora. Relatively high microbial diversity and stable community structure for the resistant cultivars were detected. Comparison analysis showed that some bacterial phyla were significantly enriched in the wheat root or rhizosphere of the resistant wheat cultivar. Furthermore, the root and rhizosphere of the resistant cultivars greatly recruited many known beneficial bacterial and fungal taxa. In contrast, the relative abundance of potential pathogens was higher for the susceptible cultivar than for the resistant cultivar. Network co-occurrence analysis revealed that a much more complex, more mutually beneficial, and a higher number of bacterial keystone taxa in belowground microbial networks were displayed in the resistant cultivar, which may have been responsible for maintaining the stability and ecological balance of the microbial community. Overall, compared with the susceptible cultivar, the resistant cultivar tends to recruit more potential beneficial microbial groups for plant and rhizosphere microbial community interactions. These findings indicate that beneficial rhizosphere microbiomes for cultivars should be targeted and evaluated using community compositional profiles. KEY POINTS: • Different resistance levels in cultivars affect the rhizosphere microbiome.. • Resistant cultivars tend to recruit more potential beneficial microbial groups. • Bacteria occupy a high proportion and core position in the microflora network.

The climate change endangers many species of the Amazon Forest. An example, in the endangered medicinal species Pilocarpus microphyllus (popularly known as jaborandi). The jaborandi is a natural source of alkaloids used for serious diseases, essential for medical use. However, the potential impacts of climate change on this species are still unknown. Thus, the objective was to evaluate the effect of high temperature and high atmospheric concentrations of CO2, projected to occur with climate change, combined with water stress, on the ecophysiology of jaborandi seedlings. For this, seedlings were exposed to three different climatic scenarios in a controlled environment, characterized as current Amazon: RCP4.5 (current Amazon average temperature + 2.5 °C and 538 ppm of [CO2]) and RCP 8.5 (+ 4.5 °C and 936 ppm of [CO2]). Within each climatic scenario, two levels of irrigation were applied: 90% (well-watered) and 40% (water-stressed) of the substrate water holding capacity. Growth variables, plant water status, fluorescence parameters, and enzymatic antioxidants activity were evaluated. The results showed that the jaborandi seedlings showed greater total dry mass production when grown in the current Amazon with no water stress. The seedlings’ growth was negatively affected by the scenarios enriched with CO2, especially RCP 8.5. Climate change scenarios had the greatest negative impact when the seedlings were subject to water stress. Under these scenarios of climate change and water stress, the seedlings allocated more carbohydrates to the root system. The negative effect of water stress on jaborandi physiology and growth was attenuated by the RCP 8.5 scenario. Our results indicated that the predicted climate changes negatively impact ecophysiology jaborandi, being a threat to the extinction of this species.

In this study we tested the hypotheses that root classes would exhibit distinctive anatomical and architectural responses to drought stress, and that those responses would vary along the root axes. The root systems of four maize (Zea mays L.) sweet corn genotypes designated SC1, SC2, SC3 and SC4 were phenotyped under well-watered and drought treatments in greenhouse mesocosms, permitting increasing stratification of moisture availability as the drought progressed. Anatomical and architectural responses to drought were evaluated for each root class. Lignin distribution was assessed by image processing of UV-illuminated root cross-sections acquired by laser ablation tomography. The two cultivars with less biomass reduction under drought, SC3 and SC4, substantially enhanced lateral root development along the apical segments of axial roots when plants were grown with drought stress. These segments grew into the deeper part of the mesocosm where more moisture was available. Apical segments of the axial and large lateral roots from drought-stressed plants were thicker and had greater theoretical axial water conductance than basal segments, especially in SC3 and SC4. Basal segments of crown roots of SC3 and SC4 showed increased lignification of the stele under drought. Root anatomical and architectural responses to drought are complex and vary among cultivars and root classes, and along root axes. Drought-induced proliferation of lateral roots on apical segments of axial roots would be expected to enhance deep water acquisition, while lignification of axial roots could help preserve axial water transport.

Arbuscular mycorrhizal (AM) fungi are intimately associated with fine roots and are involved in nutrient acquisition. However, little information is available on the links between roots of individual orders and fungus colonization and community structure. Our aim was to elucidate AM fungal communities in the fine root systems of the temperate coniferous tree species, Cryptomeria japonica (Cupressaceae). We characterized the morphological traits of AM fungi microscopically and determined the community structure of AM fungi using metabarcoding with an Ion Torrent Personal Genome Machine (PGM) focusing on lower-order roots from first to third order roots. Paris-type and Arum-type AM morphologies were both generally more prevalent on first-order roots than on second- or third-order roots, but the colonization rates by the Paris type were higher than those by the Arum type. We found a total of 48 fungal operational taxonomic units dominated by Glomeraceae, and all the AM taxa detected on third order roots were also found on first and/or second order roots. In the case of the second and third orders, AM fungal communities were affected by soil conditions: electrical conductivity, pH, and N concentration. These results suggest that the abundance and species richness of AM fungi vary among lower root order systems, and that the AM community is sensitive to soil conditions and turns over as roots age.

This study aimed at understanding the uptake pathway of combined copper, zinc, and molybdenum applied to soybean (Glycine max (L.) Merrill) and maize (Zea mays (L.) seeds and their effect on seedling development. Two doses—2 and 4 mL kg−1 seeds—of a mixed copper, zinc, and molybdenum formulation were applied on both seed species, and process efficiency, i.e., how much of the applied solutions were transferred to the seeds, was determined. The spatial distribution of these nutrients was examined through microprobe X-ray fluorescence spectroscopy, and the effects on seed germination and seedling’s root and shoot development were recorded. Besides, the fraction of applied nutrients transferred from the seeds up to the seedlings tissues and the efficiency of the coating process were quantified. The results showed that seed treatments presented an overall efficiency of 70%. Most of the nutrients applied remained attached to the seed surface, i.e., seed coat or pericarp tissues in both species, being transferred to the soil afterwards. Only a tiny fraction of zinc, copper, and molybdenum was found in root and shoot tissues germinated from the coated seeds. The treatments did not impair seed germination or affected the content of the other mineral elements in the root and shoot tissues, although it had promoted a slight increase on maize’s root tissue length and dry mass. These results bring to light that the current seed treatment transfers part of the nutrients directly to the early developing seedling, while the remaining is precisely deposited in the soil volume where the root system will develop.

To investigate the effects of the spatial distribution of rice root systems on dissolved CH4 and CH4 emissions and the CH4 transport efficiency of aboveground plant parts in paddy fields. A two-year field and leaf cutting experiment was conducted on seven rice varieties, and we determined the dynamics of CH4 emissions, root system traits and dissolved CH4 concentrations in different soil layers, and the CH4 transport efficiencies of the leaf and stem sheath. CH4 emissions, the root distribution and the distribution of dissolved CH4 concentration showed large discrepancies among the different rice varieties. Correlation analysis and structural equation modeling (SEM) revealed that CH4 emissions had strong negative associations with root morphological traits (root dry weight, root area index and root volume density) and a clear positive correlation with dissolved CH4 concentrations in the 0–20 cm soil layer. In addition, the root system had an indirect negative correlation with CH4 emissions by influencing the dissolved CH4 concentrations. Furthermore, root traits had strongly positive correlations with grain yield. In the aboveground parts, the CH4 transport efficiencies of the leaf (20–70%) and stem sheath (30–80%) presented large differences among the different rice varieties, and CH4 emissions exhibited significant positive correlations with leaf CH4 transport efficiency and leaf dry weight. Our results suggest that varieties with larger and deeper root distributions and lower leaf dry weight can decrease CH4 emissions in paddy fields and maintain higher grain yield.

International audience; Although studied for more than a century, the spatial distribution of microorganisms in a root system still remains partly understood. In a repeated greenhouse experiment using the model plant Brachypodium distachyon, we investigated the composition and distribution of rhizosphere bacteria and their response to inoculation with artificially selected microbial communities, using two different sampling scales: root sections from distinct individual roots (apical, middle, and rear sections) and the remaining entire system recovered after homogenization. Using 16S rRNA gene sequencing, we identified that root section identity was the most influential factor on the microbiota composition (R2 = 44.4%), followed by batch (R2 = 34.4%), and plant identity (R2 = 15.2%). Apical sections were characterized by increased abundances for Firmicutes members, while the rear sections featured more Verrucomicrobia. Root section sampling showed better sensitivity at detecting significant effects of the inoculation on the microbiota composition (e.g., local influence of inoculation on rear sections), in contrast, the homogenized sampling showed improved reproducibility (e.g., smaller sample dispersion). The comparison of the two sampling strategies highlighted a clear tradeoff between reproducibility and sensitivity, encouraging to complement traditional approaches with fine-scale sampling to improve our capacity to understand biological effects that could be otherwise missed.

Electrical capacitance (EC) is widely used to measure root traits especially in hydroponic and wet soil environments, but its feasibility was recently questioned due to the possible leakage of electrical current before entering the root system. To investigate whether the current can travel deeper in woody roots, EC was evaluated in cotton (Gossypium hirsutum L.) grown under different soil moisture conditions (two rounds of pot experiments, one PVC tube experiment and one field experiment). In these experiments, electrical capacitance of the root (ECroot) was recorded before and after severing roots, and immediately afterward, the roots were collected to measure root dry weight, surface area, length, and volume. The results showed that ECroot was significantly reduced after root cutting especially under dry conditions in the three experiments. The PVC tube experiment further demonstrated that root cutting did not significantly affect the changes in ECroot measured at different soil layers under dry conditions possibly suggesting that the current could flow into the deep roots under these conditions. Moreover, incorporating root tissue density and soil moisture into the prediction model can improve the predictive accuracy of ECroot. In contrast, ECroot was less affected by root cutting under wet soil conditions, indicating that it may not directly measure roots under these conditions. ECroot shows the potential to directly quantify root traits under dry conditions rather than wet conditions.

Conspecific seagrass living in differing environments may develop different root system acclimation patterns. We applied X-ray computed tomography (CT) for imaging and quantifying roots systems of Zostera japonica collected from typical oligotrophic and eutrophic sediments in two coastal sites of northern China, and determined sediment physicochemical properties that might influence root system morphology, density, and distribution. The trophic status of sediments had little influence on the Z. japonica root length, and diameters of root and rhizome. However, Z. japonica in oligotrophic sediment developed the root system with longer rhizome node, deeper rhizome distribution, and larger allocation to below-ground tissues in order to acquire more nutrients and relieve the N deficiency. And the lower root and rhizome densities of Z. japonica in eutrophic sediment were mainly caused by fewer shoots and shorter longevity, which was resulted from the more serious sulfide inhibition. Our results systematically revealed the effect of sediment trophic status on the phenotypic plasticity, quantity, and distribution of Z. japonica root system, and demonstrated the feasibly of X-ray CT in seagrass root system research.

Arbuscular mycorrhizal fungi (AMF) represent an important group of root symbionts, given the key role they play in the enhancement of plant nutrition, health, and product quality. The services provided by AMF often are facilitated by large and diverse beneficial bacterial communities, closely associated with spores, sporocarps, and extraradical mycelium, showing different functional activities, such as N2 fixation, nutrient mobilization, and plant hormone, antibiotic, and siderophore production and also mycorrhizal establishment promotion, leading to the enhancement of host plant performance. The potential functional complementarity of AMF and associated microbiota poses a key question as to whether members of AMF-associated bacterial communities can colonize the root system after establishment of mycorrhizas, thereby becoming endophytic. Root endophytic bacterial communities are currently studied for the benefits provided to host plants in the form of growth promotion, stress reduction, inhibition of plant pathogens, and plant hormone release. Their quantitative and qualitative composition is influenced by many factors, such as geographical location, soil type, host genotype, and cultivation practices. Recent data suggest that an additional factor affecting bacterial endophyte recruitment could be AMF and their associated bacteria, even though the mechanisms allowing members of AMF-associated bacterial communities to actually establish in the root system, becoming endophytic, remain to be determined. Given the diverse plant growth–promoting properties shown by AMF-associated bacteria, further studies are needed to understand whether AMF may represent suitable tools to introduce beneficial root endophytes in sustainable and organic agriculture where the functioning of such multipartite association may be crucial for crop production.

Detecting belowground chemical contamination is a challenging environmental problem due to subsurface heterogeneity and limited monitoring capabilities associated with labor-intensive, intrusive, and costly sampling techniques. With their extensive root systems, vascular plants are an easily accessible aboveground link to the subsurface. Therefore, plant tissues, particularly tree cores, are used in phytoscreening applications for detecting belowground chemical contaminants. While phytoscreening has been evolving as an alternative to traditional sampling, this method has caveats: (a) easier to harvest tissues such as leaves and twigs tend to exhibit lower concentrations than tree cores; (b) coring can negatively influence tree health; and (c) trees may be unavailable for sampling at all sites. Therefore, less invasive techniques that incorporate plants other than trees could be more effective phytoscreeners. Here, we explore the use of insect-induced plant galls–that can be found on many vascular plant species–for their phytoscreening capabilities. Driven by observations that they can act as sinks for extraordinary high concentrations of nutrients during development, we tested the following hypothesis: galls will accumulate belowground chemical contaminants in higher concentrations compared to other aboveground plant tissues. Specifically, we measured and compared the concentrations of two contaminant types, inorganic heavy metals (HMs) and a volatile organic compound (VOC) and known human carcinogen, 1,4-dioxane, in four aboveground plant tissue types (leaf, twig, core, fruit) and insect-induced plant gall, across three plant types (shrub, tree, vine) sampled from contaminated areas. Twelve different HMs were present in shrubs, and 1,4–dioxane was present in both trees and vines; however, the concentrations of each contaminants varied quantitatively across plant tissue types. While galls accumulated the lowest concentrations of HMs, they accumulated the highest concentration of 1,4-dioxane, at five-times that of tree cores. Given they can be found on many vascular plant species and are easy to collect when they are locally abundant, with further development, galls may be a powerful alternative for detecting belowground chemical contamination, particularly for VOCs in urban areas. We discuss the dichotomy in the ability of galls to detect inorganic HMs versus VOCs, and outline future questions that should be considered to further develop galls for phytoscreening application.

Key message Root-specific expression of a cytokinin-degrading CKX gene in maize roots causes formation of a larger root system leading to higher element content in shoot organs. Abstract The size and architecture of the root system is functionally relevant for the access to water and soil nutrients. A great number of mostly unknown genes are involved in regulating root architecture complicating targeted breeding of plants with a larger root system. Here, we have explored whether root-specific degradation of the hormone cytokinin, which is a negative regulator of root growth, can be used to genetically engineer maize (Zea mays L.) plants with a larger root system. Root-specific expression of a CYTOKININ OXIDASE/DEHYDROGENASE (CKX) gene of Arabidopsis caused the formation of up to 46% more root dry weight while shoot growth of these transgenic lines was similar as in non-transgenic control plants. The concentration of several elements, in particular of those with low soil mobility (K, P, Mo, Zn), was increased in leaves of transgenic lines. In kernels, the changes in concentration of most elements were less pronounced, but the concentrations of Cu, Mn and Zn were significantly increased in at least one of the three independent lines. Our data illustrate the potential of an increased root system as part of efforts towards achieving biofortification. Taken together, this work has shown that root-specific expression of a CKX gene can be used to engineer the root system of maize and alter shoot element composition.

Morpho-physiological characteristics in Eucalyptus species can determine N (NUE) and P (PUE) use efficiency and, consequently, the plant's responses to fertilization. The study aimed to evaluate whether morphological and physiological characteristics of seedlings from Eucalyptus species affect the N and P use efficiency. For this, in a greenhouse, Eucalyptus grandis (GPC 23) and Eucalyptus saligna (32864) clones were grown in Hoagland nutrient solution for 21 days, followed by N and P restriction in CaSO4 solution 0.1 mol L−1 during 15 days. Morphological parameters from shoot and root system, dry mass of organs, photosynthetic pigments concentration, and chlorophyll a fluorescence of Eucalyptus species were evaluated, and NUE and PUE were calculated. Eucalyptus grandis presented the highest NUE and PUE values. The highest surface area, volume, and roots length values contributed to these results, justifying the highest dry mass production from leaves, stem, roots, and plant. Eucalyptus saligna presented the lowest NUE and PUE values, which negatively influenced photosynthesis (higher F0 values and lower concentrations of photosynthetic pigments). Root morphological parameters had a strong relationship with NUE and PUE and can be used to select Eucalyptus species, and breeding programs, as they can predict the ability of development of Eucalyptus species under low N and P availability.

Cytokinin is a plant hormone and an important regulator of root growth. Reduced cytokinin levels increase root systems, which can be beneficial for crops grown on nutrient poor and/or dry soils. Our study analyzed the effects of increased cytokinin oxidase 5 (OsCKX5) expression in rice roots on root morphology, architecture, and nutrient uptake. We fused the OsCKX5 gene to the strong, root-specific RCc3 rice promoter and overexpressed it in rice plants. The root-specific expression of OsCKX5 in the transgenic plants resulted in positive effects on root development without compromising shoot growth. The root system of the transgenic plants exhibited greater volume, length, projection area, a higher number of tips, and enhanced surface area. OsCKX5 overexpression also resulted in an increased uptake ability of certain macro- and micronutrients, a greater root biomass, deeper root system, and a higher root:shoot ratio, when cultivated on low-fertility soils. We conclude that the enhanced root growth and development by root-specific expression of OsCKX5 could be advantageous for crops grown on oxidic soils in the tropical regions, with a low availability of certain nutrients, especially P and Zn.

Bromeliads with water-impounding tanks uptake water and nutrients by the leaf-absorbing trichomes present on the leaf surface while the compact root system functions as for plant anchorage on other plants. However, recent studies showed a clear role of the bromeliad roots in nutrient absorption and subsequently improving plant growth. Accordingly, the present study aimed to compare the uptake and assimilation of inorganic and organic nitrogen by roots and leaf-absorbing trichomes of silver vase bromeliad (Aechmea fasciata). As treatments, plants were fertilized with 0, 15 or 30 mM nitrogen (N) as either urea or ammonium nitrate applied into the tank or on the substrate (roots). Dry biomass, number of leaves, macro and micronutrient contents in leaves, chlorophylls a, b, and total carotenoids were determined. In addition, gas exchange, chlorophyll fluorescence, and nitrogen efficiency indexes were analyzed. The results showed that ammonium nitrate is taken up either by leaf-absorbing trichomes and or by roots of silver vase bromeliad. Plants fertilized with ammonium nitrate had an increase in leaf nitrogen content with the increase of nitrogen concentrations on tank. However, these increases did not result in biomass accumulation or changes in the photosynthetic apparatus. Our results showed that the roots of silver vase bromeliad are more efficient for inorganic nitrogen.

In-situ field studies were conducted for three consecutive baby corn (Zea mays L.) growing seasons to quantify the amount of reactive N flowing beyond the rhizosphere while defining mitigation strategies. The N applications based on plant need were agronomically more efficient than the fixed-time blanket N applications. Average area-scaled leachate N losses in the winter season were 24 and 8% higher than the summer and spring seasons, respectively. A smaller root system at low N rate likely restricts plant N uptake and accelerates the magnitude of N leaching factor ranging from 6 to 9% in different seasons. Leachate N-flux peaks were more pronounced at early growth stages, attributed to the N supply in excess of the plant need. Residual soil mineral N varied little despite a wide range of fertilizer N rates, hence there was no evidence to support the idea that soils should be replenished for N removal by crops at fixed growth stages. Rather, N losses to the environment were greater using fixed-timing blanket N applications, which can be mitigated by a shift to N fertilization based on assessment of plant need. Use of the PAU-leaf colour chart and chlorophyll meter to guide need-based fertilizer N topdressings reduced average leachate NO3¯-N load by 69% over blanket N use practice, while producing an average 17% higher cob yield in baby corn. Hence, the blanket N use practices should be replaced with need-based N management strategies to mitigate environmental footprints of N use in the baby corn based cropping system.

To control agronomic N losses and reduce environmental pollution, biological nitrification inhibition (BNI) is a promising strategy. BNI is an ecological phenomenon by which certain plants release bioactive compounds that can suppress nitrifying soil microbes. Herein, we report on two hydrophobic BNI compounds released from maize root exudation (1 and 2), together with two BNI compounds inside maize roots (3 and 4). On the basis of a bioassay-guided fractionation method using a recombinant nitrifying bacterium Nitrosomonas europaea, 2,7-dimethoxy-1,4-naphthoquinone (1, ED50 = 2 μM) was identified for the first time from dichloromethane (DCM) wash concentrate of maize root surface and named “zeanone.” The benzoxazinoid 2-hydroxy-4,7-dimethoxy-2H-1,4-benzoxazin-3(4H)-one (HDMBOA, 2, ED50 = 13 μM) was isolated from DCM extract of maize roots, and two analogs of compound 2, 2-hydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one (HMBOA, 3, ED50 = 91 μM) and HDMBOA-β-glucoside (4, ED50 = 94 μM), were isolated from methanol extract of maize roots. Their chemical structures (1–4) were determined by extensive spectroscopic methods. The contributions of these four isolated BNI compounds (1–4) to the hydrophobic BNI activity in maize roots were 19%, 20%, 2%, and 4%, respectively. A possible biosynthetic pathway for zeanone (1) is proposed. These results provide insights into the strength of hydrophobic BNI activity released from maize root systems, the chemical identities of the isolated BNIs, and their relative contribution to the BNI activity from maize root systems.

Mowing is a common management practice in grassland ecosystems. However, how mowing affects fine root dynamics remains poorly explored. A field experiment was conducted to study how mowing influences root dynamics in artificial and natural grasslands for three consecutive years with root-window method. Root production among the treatments varied from 312 to 681 m m−2 each year and fine root turnover varied between 1.58 and 3.41 times per year. Fine root production, root mortality and root standing crop exhibited clear seasonal patterns in both the natural and artificial grasslands, and these were mainly driven by precipitation and temperature. Root production and root turnover responded differently to mowing in different types of grassland. In the artificially restored grassland, mowing significantly increased root production and root turnover (15.01% and 13.06%, respectively) and decreased the root lifespan by 14.60%. In contrast, none these effects were significant in the naturally restored grassland. The mowing-induced increase in root production and root turnover in the artificially restored grassland was mainly due to an enhancement in aboveground biomass and soil moisture. However, the lack of an effect on these parameters from mowing in the naturally restored grassland may be due to the higher species diversity. Our findings demonstrate that mowing might accelerate root turnover and improve belowground productivity in the artificially restored grassland, highlighting that suitable mowing is an efficient way to manage artificial grasslands from the perspective of the dynamics of root system.

Baru (Dipteryx alata Vogel) is a native tree plant, widely distributed in Brazil, and has a growth and development in acidic soils like Cerrado, indicating a probable tolerance to adverse soil conditions, such as the high concentration of metals and the acidic pH. Due to the lack of information about the tolerance of this species to metals and the possibility of being used in the recovery of degraded areas and/or in phytoremediation, this work was developed with the objective of evaluating the in vitro germination and growth capacity of baru in medium supplemented with different concentrations of aluminum, iron, and manganese, as well as through chemical analysis, to determine the concentration of metals accumulated in cultivated plants in these conditions. The treatments consisted in different concentrations of metals: aluminum, Al3+ (0, 3.5, 7.0, 10.5, 21.0, or 42.0 mg L−1); iron, Fe3+ (0, 2.5, 4.9, 7.4, 14.7, or 29.4 mg L−1); and manganese, Mn2+ (0, 0.4, 0.8, 1.2, 2.4, or 4.8 mg L−1) added to the medium WPM. The tested values were based on using the lower concentration as the limit value, calculated based on risk to human health in accordance with CONAMA resolution 420/2009 for groundwater. At 60 days of cultivation, the percentage of germination, the average number of leaves, the length of the main root and the aerial part, the fresh and dry mass of the aerial part and the root system and the cations concentration Al3+, Fe3+ and Mn2+ in the plant biomass, were evaluated. The results showed that under the conditions in which the experiment was conducted, germination and in vitro growth of baru were not affected by the presence in high concentrations of any of the evaluated metals, with no differences in the percentage of germination and plant growth, as well as typical toxicity characteristics were not observed, such as changes in root morphology, chlorosis, or tissue oxidation. The absence of toxicity symptoms in baru plants, in the presence of Al3+, Fe3+, and Mn2+, indicate that the species is tolerant to these metals. The accumulation of Al3+ and Fe3+ in the plant biomass at the beginning of growth, simultaneously with the increase in the concentrations of these elements in the culture medium, indicates that this species can be used for phytoremediation, because it is a probable accumulator of these elements throughout its development, given the presence in significant concentrations of these elements also in the seeds.

Improvement in rainfed finger millet productivity is close to stagnation from the last decade due to insufficient above-ground biomass which includes vegetative shoot mass, grain-bearing ear-heads and their size. As the partitioning of biomass to sink traits has reached reasonably high, an increase in shoot mass is expected to improve the yields further. The shoot mass is primarily dependent on the root system, hence, the root growth pattern at different crop growth stages and their relationship to shoot mass was studied under well-watered (WW) and drought stress (DS) conditions. Results revealed that, the mean root length increased by twofold from 15 to 30 DAS followed by a marginal increase up to 75 DAS under WW condition. While the root dry weight had a slow increase up to 45 DAS and rapid growth afterwards under WW condition. The DS during tillering (15 to 30 DAS) and later vegetative stage (35 to 55 DAS) increased the root length marginally, whereas, the root dry weight and shoot dry weight were decreased substantially and; recovered to > 80 and nearly 70% respectively after the alleviation of DS. The root dry weight was positively and significantly related with shoot mass at all stages up to 55 DAS in WW and up to 45 DAS in DS, whereas the root length at 45 DAS only under WW and DS conditions. Therefore, rapid deep root and particularly the root mass at tillering have relevance in shoot mass production, especially under DS conditions.

Fine roots are the most active and functional component of root systems and play a significant role in the acquisition of soil resources. Density is an important structural factor in forest plantations but information on changes in fine roots along a density gradient is limited. In this study, plantations of black locust (Robinia pseudoacacia L.) and Chinese pine (Pinus tabuliformis Carr.) with four density classes were analyzed for the influence of soil and leaf traits on fine root growth. Fine root biomass increased with stand density. High fine root biomass was achieved through increases in the fine root production and turnover rate in the high-density black locust plantations and through an increase in fine root production in the pine plantations. In the high-density Chinese pine stand, there was a high fine root turnover which, coupled with high fine root production, contributed to a high fine root biomass. Overall, fine root production and turnover rate were closely related to soil volumetric water content in both kinds of plantations, while fine root biomass, especially the component of necromass, was related to soil nutrient status, which refers to phosphorous content in black locust plantations and nitrogen content in Chinese pine plantations. There was a close linkage between leaf area index and fine root dynamics in the black locust plantations but not in the pine plantations.

The characteristics of soil holding capacity for different shrub-grass patterns are important to research the mechanisms regulating vegetation on slopes. The objective of this study was to describe the characteristics and mechanisms of soil erosion and hydraulic parameters under different vegetation patterns in the Pisha sandstone area of Inner Mongolia on lands of 8° slope gradient. We carried out field scouring experiments on five different shrub-grass patterns as treatments, viz no shrubs (GL), shrubs on the upper part of the slope (SU), middle part of the slope (SM) and lower part of the slope (SL). We designated bare slope (BL) as the control. We employed three different water flow rates (15, 20, 30 L·min−1). Our results showed that the contribution of plant root systems to slope sediment reduction ranged from 64 to 84%. The root systems proved to be the main contributing factor to reduction of erosion by vegetation. The relationship between soil detachment rate, stream flow power, and flow unit stream power under different scouring discharge rates showed that soil detachment declined in rank order as: BL > GL > SU > SM > SL. The SL pattern had the lowest soil detachment rate (0.098 g·m−2·s−1), flow stream power (2.371 W·m−2), flow unit stream power (0.165 m·s−1) and flow shear stress (16.986 Pa), and proved to be the best erosion combating pattern. The results of decision coefficient and path analysis showed that stream power was the most important hydraulic parameter for describing soil detachment rate. The combination of stream power and shear stress, namely Dr = 0.1ω − 0.03τ − 0.56 (R2 = 0.924), most accurately simulated the soil detachment characteristics on slopes. Our study suggests that the risk of soil erosion can be reduced by planting shrub-grass mixes on these slopes. Under the conditions of limited water resources and economy, the benefit of sediment reduction can be maximized by planting shrubbery on the lower parts of slopes.

Though competition operates distinctly above and below ground, competition with near neighbours explained more variation in crown and root system morphology of young tropical trees than did abiotic conditions. Comparisons of above- and below-ground tree architecture and variation remain scarce in the literature of competition dynamics in forests. Trees compete above and below ground with neighbours, but the extent of such a neighbourhood and the relative importance of above- or below-ground neighbours in determining tree growth rates remain poorly understood. We combined terrestrial laser scans and a root excavation campaign in the tropical planted Sardinilla forest experiment with annual diameter-at-breast height measurements to test how the crowns and root systems of five tropical tree species (N = 128) varied with biotic neighbourhood and abiotic environmental characteristics. Crown and root system extent were compared, and the Hegyi competition index calculated at three spatial scales was regressed on focal tree biomass. We identified which neighbourhood and environmental variables explained most of the variation in mean crown and root system extent and compactness (a measure of morphological homogeneity) at the plot level and for species separately. Root systems were 2.6 ± 1.1 times wider than crowns on average and focal tree biomass was the best predicted by competition with near neighbours. At the plot level, more variation in crown and root system traits was explained by biotic than abiotic characteristics (65.8 and 26.0%, respectively). More intense competition in the near neighbourhood reduced crown extent of one study species (Anacardium excelsum) and root system extent of 4 out of 5 study species, and it also led to more compact crowns and root systems of Tabebuia rosea. After accounting for spatial autocorrelation in focal tree location, soil nitrogen concentration was not found to significantly affect the studied morphological traits. These results emphasize the role of competition in determining tree morphology generally, while also supporting the claim that competition operates distinctly above and below ground.

In this study, pepper (Capsicum annuum L.) inbred lines were grafted onto different rootstock genotypes and tested under saline conditions. A hydroponic experiment was conducted in nutrient solution growth system in a growth chamber of Erciyes University, Agricultural Faculty in Kayseri, Turkey. The experiment was conducted in spring 2017 growth season. Two pepper inbred lines (ERu-462 and ERu-1227) were grafted onto three different pepper rootstocks/genotypes (Scarface F1, 11B14, and Yaocali F1) and grown in 8 L pots filled with continuously aerated nutrient solution under saline conditions (8 dS m(-1)) with three replications. The growth chamber experiment was carried out to determine the effects of salt stress on plant growth, shoot and root dry weights, leaf area, photosynthesis, leaf total chlorophyll (a + b) and carotenoid content, proline content, glycine betaine content, leaf electrolyte leakage, leaf and root macro element concentration in grafted and non-grafted pepper plants. The results indicated that ERu-462 grafted on to Scarface and 11B14 rootstock genotypes were more tolerant to salinity than ERu-1227 in term of leaf chlorophyll (a + b) content and leaf carotenoid content, photosynthesis, and proline content. Though, higher shoot and root biomass, leaf area formation, root K+, Na+, Cl- contents were observed when ERu-1227 grafted on to Scarface and 11B14 rootstock genotypes. Strong rootstock promoted plant growth in pepper plant both under control and saline conditions and significant depression of plant biomass production under saline conditions was observed in both grafted and non-grafted plants. However, grafting onto vigorous rootstocks alleviated negative effects of salinity stress on pepper plants. Scarface and 11B14 were found more tolerant to salinity than non-grafted pepper plants and the other genotypes used as regard to investigated parameters.

The impact of inorganic pollutants in the zone of industrial wastewater settling tanks (South of Russia) was studied. The levels of Mn, Cr, Ni, Cu, Zn, Pb, Cd were determined for Verbascum thapsus L., which are part of the mesophilic succession of wild plants in the studied technogenically polluted territory. The bioavailability of heavy metals (HM) for plants from transformed soils has been established. Anatomical and morphological features in the tissues of the plants affected by HM were analyzed using light-optical and electron microscopic methods. Contamination of the soil cover with Mn, Cr, Ni, Cu, Zn, Pb and Cd has been established with maximum content of Zn. It was revealed that the HM content in the V. thapsus plants exceeded the maximum permissible levels (Russian state standard): Zn by 23, Pb by 2, Cr by 31 and Cd by 3 times. The lower level of HM content in the inflorescences of mullein plants in comparison with the root system, stems and leaves indicates the resistance of generative organs to technogenic pollution. In the root and leaves of the V. thapsus, the anatomical and ultrastructural observation were carried out using light-optical and transmission electron microscopy. Changes in the ultrastructure of plants under the influence of anthropogenic impact have been revealed. The most significant changes of the ultrastructure of the polluted plants were found in the cell organelles of leaves (mitochondria, plastids, peroxisomes, etc.) including spatial transformation of the thylakoid system of plastids during the metal accumulation by plants, which may determine the mechanism of plant adaptation to technogenic pollution.

To cope with heavy metal stress, plant root systems undergo root structure modification and release of multifarious metabolites. Elucidation of the resistance strategies to heavy metals mediated by the root system is crucial to comprehend the resistance mechanisms of plants. Here two rice cultivars with contrasting grain cadmium (Cd) accumulation traits were selected and the responses of their root systems to Cd stress were evaluated by morphological and metabolomics analysis. The phenomic and metabolomic responses of the root system varied between the two cultivars under Cd stress. The low-Cd accumulation rice cultivar (TY816) had a more highly developed root system that coped with Cd stress (10 µM) by maintaining high root activity, while the root cells of the high-Cd accumulation cultivar (JY841) lost viability due to excessive Cd accumulation. TY816 upregulated lipids and fatty acids to reduce Cd uptake, whereas JY841 upregulated phenylethanoid glycosides to cope with Cd-induced oxidative stress. The combination of metabolomics and phenomics revealed that rice roots employ multiple strategies to increase their tolerance of Cd-induced oxidative stress. Differing capacities to shape the root system architecture and reprogram root exudate metabolites may contribute to the contrasting Cd accumulation abilities between JY841 and TY816.

It has been reported that root characteristics and canopy structure in an agroforestry system directly change the availability of underground and aboveground resources and climatic conditions and seriously affect crop growth and yield (Dufour et al. in J Agron Crop Sci 199: 217–227, 2013; Bouttier et al. in Agroforest Syst 88: 693–706, 2016; Farooq et al. in Appl Ecol Env Res 17: 3553-3566, 2019). An experiment was conducted in northwest China to explore the distribution and characteristics of root systems for alfalfa grown in a poplar/alfalfa silvopastoral system. Field sampling was conducted every 15 days in a 3-yr-old alfalfa + 7-yr-old poplar silvopastoral system, a 3-yr-old sole-alfalfa system, and a 7-yr-old sole-poplar system. The results showed that intercropping reduced the RLD of alfalfa, while the FSRL of intercropped alfalfa was higher than that of sole-cropped alfalfa. In terms of the agronomic traits of alfalfa (plant height, leaf area index, leaf-stem ratio, growth rate), intercropping traits were significantly lower than sole-cropped alfalfa, and the total hay yield during intercropping was 55.27% lower than that of sole-cropped alfalfa. In terms of field microclimate, the dew point temperature and wind speed of sole-cropped alfalfa were 70.68% and 93.83% higher than that of intercropping, but the air humidity of sole-cropped alfalfa was 13.49% lower than that of intercropping, and there was no significant difference in air temperature. The crude protein (CP), crude fat (CF), and relative feed value (RFV) of intercropping alfalfa were 17.78%, 12.33%, and 17.26% higher than sole-cropped alfalfa, respectively. Although the agronomic traits and yield of alfalfa decreased with intercropping, intercropping could improve the microclimate and the quality of alfalfa significantly. The land equivalent ratio (LER = 1.42) in the poplar/alfalfa silvopastoral system was > 1, indicated that the system in advantageous.

To assess whether grafting could improve the nitrogen (N) efficiency of potato cultivars and to determine which physiological and morphological characteristics are predominantly contributing to N efficiency, a hydroponic experiment was conducted. Two contrasting potato cultivars (Agria: N-efficient and Van Gogh: N-inefficient) were grafted reciprocally onto each other. Grafted and non-grafted control plants were grown in a growth chamber for 42 days in 8 L pots filled with continuously aerated nutrient solution under two N rates (Low-N : 0.5 mM N and High-N : 3.0 mM N) by using a deep water culture (DWC) technique. The shoot and root fresh (FW) and dry (DW) weights, main stem length, number of leaves, total leaf area, photosynthetic activity of leaves, shoot and root N concentration, total N uptake, total root length and root volume of potato plants were significantly increased with increased N rate. The grafted plants produced significantly higher above ground biomass than non-grafted ones, indicating that N efficiency was significantly improved by the reciprocally grafting under low and high N rates. Non-grafted cv. Agria showed higher numbers of shoot and root FW and DW, total leaf area, intensity of photosynthesis net measurements, compared to non-grafted cv. Van Gogh under both N rates. In reciprocal grafting, the growth performance of cv. Agria slightly increased when it was grafted onto cv. Van Gogh, whereas a significant increase in crop growth performance was recorded when cv. Van Gogh was grafted onto cv. Agria. The N efficiency of non-grafted cv. Agria was closely associated with its vigorous root growth and active root system under both N conditions. Same root morphological characteristic could not be exhibited by the N-inefficient cv. Van Gogh. Our study suggested that root morphological characteristics are contributing more than shoot characteristics to N efficiency of potatoes. These traits could be useful characters to breed/select N-efficient potato rootstocks for sustainable agriculture in the future.

A root system is splint if it is a decomposition into a union of two disjoint root systems. Examples of such root systems arise naturally in studying embeddings of reductive Lie subalgebras into simple Lie algebras. Given a splint root system, one can try to understand its branching rule. In this paper we discuss methods to understand such branching rules, and give precise formulas for specific cases, including the restriction functor from the exceptional Lie algebra $\mathfrak {g}_{2}$ to $\mathfrak {sl}_{3}$ .

It is well established that mycorrhizal symbiosis can affect plant-plant interactions. On the other hand, how intraspecific plant interactions influence communities of arbuscular mycorrhizal fungi (AMF) is still very poorly understood. We applied 454 pyrosequencing to determine the responses of AMF communities to intraspecific shoot and root interactions using Medicago sativa L. as host plant. We found that intraspecific plant interaction caused significant variation in the structure of the AMF community assessed from roots but not from soil. Intraspecific root system interaction resulted in significantly elevated AMF species richness, greater total mycorrhizal and arbuscular colonization, and a larger root:shoot ratio compared to plants experiencing intraspecific shoot interaction or no interaction. Intraspecific shoot interaction resulted in significantly depressed AMF species richness. Our results support two hypotheses. The first is that increased AMF species richness in plants experiencing intraspecific root interaction originates from competitive release provided by high root density. The second is that shoot interaction leads to reduced allocation to root systems, increasing the stringency with which host plants selectively reward the most cooperative fungi. Because intraspecific interactions among host plants can influence the structure of their AMF community, interactions among species in complex plant communities may influence AMF community structure in addition to a plant diversity effect.

Eupatorium glandulosum of Asteraceae family is an important medicinal plant used to cure various diseases by tribal populace. In the present study, a protocol for mass propagation of Eupatorium glandulosum has been developed from nodal explants cultured in the MS basal medium supplemented with various concentrations and combinations of IAA and BA. The maximum rate of proliferation of shoots per explants (59.66 ± 1.76) was observed in the medium containing 0.5 mg/l of IAA and 3 mg/l of BA, but medium with 1 mg/l of IAA and 4 mg/l of BA showed the maximum shoot length. When the regenerated shoots were rooted in vitro on MS basal medium supplemented with various concentrations of IAA and IBA, medium with 4 mg/l of IBA induced more number of roots per shoot (32.67 ± 0.89) while maximum root length (6.1 ± 0.12 cm) was recorded in 3 mg/l of IBA. The plantlets, with well developed root systems, were successfully acclimatized and transferred to the pots containing a mixture of Soil, Sand and Coco peat (1:1:1) with 100% survival rate. The research article tends to elucidate the tissue cultural techniques for the mass propagation and sustainable utilization of Eupatorium glandulosum. This technique could be implemented for the continuous extraction of valuable medicinal components in the pharmaceutical industry.

The objective of the study was to associate soil moisture, aerial biometric characteristics, and root distribution patterns in the yield of sugarcane genotypes in the fourth ratoon and the relationships between these characteristics. We used five sugarcane genotypes (CTC9002, RB044311, RB044313, RB044336, and RB867515) and five soil depths (0–20, 20–40, 40–60, 60–80 and 80–100 cm deep). The evaluations were carried out in December 2019. We evaluated the root systems, the soil water content at the five depths, the aerial biometric characteristics, and the productive yield. In the roots, the genotypes RB044311, RB044313, RB044336, and RB867515 showed a higher yield. On average, genotypes showed 50% of dry weight and total root length at a depth of 0–20 cm, 73% between 0 and 40 cm, and 86% between 0 and 60 cm. The RB044336 genotype showed maximum height and number of buds. The RB867515 genotype had the largest average stem diameter and CTC9002, the largest number of tillers. The genotypes CTC9002 and RB867515 presented the highest soluble solids' content, apparent sucrose in the juice, and total reducing sugars. These genotypes showed a 26% and 57% higher root density in soil layers at depths of 60–80 cm, respectively, 79% and 86% in the 80–100 cm layer, about the layer with the highest concentration of 0–20 cm roots. These layers remained with the highest soil moisture levels during the period of establishment and intensive cultivation growth. Thus, there was a relationship between root distribution dynamics and soil moisture in different areas.

The use of chia (Salvia hispanica L.) seeds as functional food is increasing worldwide and research on plant traits is important as the crop spreads. The seedling stage has been identified as crucial for establishment, survival, and competition with weeds but information on chia at this stage is scanty, especially regarding root traits. In this study, 8 genotypes of chia: 4 populations (Australia, Mexico, Peru, Basilicata) and 4 breeding lines (G3, G8, G17, WS) were evaluated under controlled conditions at two early stages (six leaves, S-6; ten leaves, S-10) with the aim to assess growth characteristics and variability in root morphological traits. The shoot height and dry matter were measured together with the following root traits: dry matter and architectural parameters characterized through image analysis of root scans: length, surface, average diameter, tips, forks and crossings. Plants showed a greater phenotypic variation at S-6 than at S-10 (average CV = 40% and 22%, respectively). A high variability was recorded for root biomass, root volume, number of forks and crossings (average CV = 54, 40, 44 and 48%, respectively), while root diameter showed lower variability (average CV = 10%). Four principal components explained more than 97% of the total variance and root length, surface area, volume and average diameter contributed mainly to the variability. Cluster analysis showed that genotypes were very different for morphological root traits. Australia and G8 had the most developed root system with longer and coarser roots. Our results could be used in a breeding program for new cultivars with a more vigorous seedling.

The root system of oil palm (Elaeis guineensis Jacq.) has characteristics unfavorable for nutrient absorption, which may cause it to be dependent on arbuscular mycorrhizal colonization. In agricultural production systems with a greater diversity of species, the arbuscular mycorrhizal colonization of mycorrhizal-dependent species can increase. Therefore, to determine whether oil palm mycorrhizal colonization varies according to the diversity of species in the system in which it is planted, we evaluated the arbuscular mycorrhizal colonization of oil palm planted in biodiverse agroforestry systems and monocultures in the Amazon. We determined the mycorrhizal colonization of fine roots (diameter ≤ 2 mm) in two management zones (“weeded circle” and “leaf pile”) of oil palm cultivated in six agroforestry systems with different compositions of plant species and in two monocultures. In general, mycorrhizal colonization was 3 times higher in oil palm cultivated in agroforestry systems than in monoculture. Mycorrhizal colonization was higher in the leaf pile zone than in the weeded circle zone, but the effect size was low and varied inversely with the P content of the soil in these management zones. The adoption of oil palm cultivation in agroforestry systems has the potential to increase mycorrhizal colonization of this species in the Amazon.

The use of arbuscular mycorrhizal (AM) fungi is considered as an effective approach to enhance plants’ growth; nevertheless, its efficacy may vary with the type of inoculum and its application method. The present study, for the first time, investigates the effects of different mycorrhizal species applied through different methods on morpho-physiological growth, root system architecture, nutrient uptake, and root exudates of maize. Four AM fungi species viz., Claroideoglomus etunicatum (C.E), Rhizophagus intraradices (R.I), Funneliformis mosseae (F.M), and Diversispora versiformis (D.V) were applied to maize through seed coating, soil application, or seed coating+ soil application. A control without AM fungi was maintained for comparison. All the thirteen treatments were arranged in completely randomized design with three replications. Application of C.E, R.I, F.M, and D.V through different methods triggered the growth performance of maize by improving morpho-physiological characteristics and root morphology, modulating AM fungi colonization, enhancing the nutrient (N, P, K) uptake, and reducing the root exudates (oxalic, malonic, fumaric, malic, citric, and T-aconitic) compared with control. Among the different mycorrhizal species, F.M applied particularly through seed coating+ soil application was more effective in regulating maize growth as compared with C.E, R.I, or D.V species owing to better root system, higher root colonization, and greater nutrient uptake in this treatment. Interestingly, seed coating of F.M recorded statistically similar or higher shoot and root growth attributes compared with soil application particularly at 30 days after sowing. In crux, F.M applied through seed coating + soil application performed better than that of other mycorrhizal species. The obtained results also suggest that seed coating can be a cheap, viable, and efficient delivery system of AM fungi particularly for large scale application, as AM fungi seed coating had faster and greater effect on maize growth compared with soil application during early growth stages.

We have reviewed publications on the physiological and ecological features of the growth and regeneration processes of Juniperus sabina L. which grows in semiarid sandy land in the Ordos plateau in northern China where desertification has progressed over time. J. sabina is a key native plant species used for ecological restoration in this region. The life history of J. sabina in this sandy land that has been revealed through this review includes several unique features: (1) both vegetative and seed propagations are observed, but seed propagation is not successful in the location where the mature J. sabina stands. Instead, seed propagation can occur at a different place with different landscapes from the mature stands. (2) Nurse plants play an important role in providing the microclimatic environment necessary for the growth of J. sabina seedlings and young plants. (3) During the horizontal and vertical growth processes of the J. sabina patch, the root system was affected by burial in shifting sand and consequently acquired greater access to the water supply in deeper soil horizons, which could support larger growth. These characteristics suggested that the regeneration by seed propagation and growth strategy of J. sabina in this region was strongly affected by sand movement and the landscape that is generated by sand movement.

Precrops exhibit vigorous deep root growth, especially when grown perennially. However, their contribution to accumulate essential nutrients derived from deeper soil layers in the topsoil has not been quantified. We determined the vertical distribution of phosphorous (P) and potassium (K) affected by contrasting root systems of 3 precrops and their effects on subsequently grown spring wheat. Three precrops (lucerne, chicory and tall fescue) were grown for 1, 2 and 3 years prior to spring wheat cultivation. We measured plant available soil P and K from 0 to 30 cm to 75–105 cm of soil depth after precropping. Root growth and crop performance of spring wheat as affected by precropping were measured in two repeated trials. We observed maximum 22-fold higher root-length density (RLD; cm cm− 3) of taprooted chicory compared with fibrous-rooted tall fescue in the subsoil. There were significant increases in plant available K in the topsoil by 27 mg kg− 1 over the precrop duration between 1 and 3 years. Grain yield of subsequently grown spring wheat was significantly increased by 10 % and 14 % from 1 year to 3 year-treatments of lucerne and chicory, respectively. Similarly, significant increases in P uptake (7 % and 19 %) and K uptake (21 and 14 %) of spring wheat was noted for the same treatments. Our data suggest that there is potential for the yield of short-season cereals to be improved by increased soil nutrient bioavailability in the topsoil derived from deeper soil layers by the deep roots of perennial precrops.

Vicia villosa Roth is a legume species with a growing application in Argentina as a cover crop (CC), a practice that favors the sustainable development of agricultural systems. However, several areas where the use of this CC provides numerous advantages are affected by high concentrations of arsenic (As). Thus, in the present work we studied hairy vetch ability to cope with arsenate [As(V)], arsenite [As(III)], and the mixture of both along with oxidative stress indexes [chlorophyll content, malondialdehyde (MDA) equivalents] as well as anatomical and histological changes in the root structure. The results obtained suggested a different behavior of hairy vetch depending on its growth stage and on metal(oid) concentration. The roots treated with the contaminant showed less turgidity, thickening of the epidermal and subepidermal parenchymal outer layers, and the presence of dark deposits. The morpho-anatomic parameters (cortex length, vascular cylinder diameter, total diameter, and vascular cylinder area) were altered in plants treated with As(V) and As(V)/As(III) whereas the roots of plants treated with As(III) did not show significant differences respect to the control. Moreover V. villosa could tolerate and remove As from soil, thus the use of this legume species seems an attractive approach to remediate As while protecting contaminated soils.

Here, we assess the differential impact of drought on root carbon metabolism in the widely cultivated alfalfa (Medicago sativa, Ms) and the model legume Medicago truncatula (Mt). Understanding how carbon allocation is regulated under drought stress conditions is a central issue to improving alfalfa productivity under future climate change scenarios. Alfalfa and Medicago truncatula were compared under water deficit conditions. Root carbon metabolism of the taproot and fibrous roots was analysed. M. truncatula drought tolerance variability was compared to that of alfalfa using six accessions of the Medicago Hapmap project. The prominent taproot is much less developed in M. truncatula than in alfalfa with the former exhibiting an extensive fibrous root system. In both examined Medicago species the taproot contained the major pools of soluble protein, sucrose and pinitol, whereas the major pools of hexoses and carbon metabolism enzymes appeared to be in the fibrous roots. Under water-deficit conditions, the response of M. sativa strongly differed from that of M. truncatula at the root level. Water deficit conditions differentially modulate the root carbon metabolism of M. sativa and M. truncatula. Mt maintained a more active carbon metabolism in the fibRs, as sucrose, myo-inositol and pinitol accumulated to cope with the water deficit (WD). Conversely, the root system of Ms did not accumulate cyclitols and carbon metabolism was more severely affected under water deficit conditions. This differentially exerted control may determine the drought response of these two close relatives.

Aluminium (Al) toxicity in acid soils inhibits root elongation and development causing reduced water and nutrient uptake by the root system, which ultimately reduces the crop yield. This study established a high throughput hydroponics screening method and identified Al toxicity tolerant accessions from a set of putative acid tolerant lentil accessions. Four-day old lentil seedlings were screened at 5 µM Al (pH 4.5) for three days in hydroponics. Measured pre and post treatment root length was used to calculate the change in root length (ΔRL) and relative root growth (RRG%). A subset of 15 selected accessions were used for acid soil Al screening, and histochemical and biochemical analyses. Al treatment significantly reduced the ΔRL with an average of 32.3% reduction observed compared to the control. Approximately 1/4 of the focused identification of germplasm strategy accessions showed higher RRG% than the known tolerant line ILL6002 which has the RRG% of 37.9. Very tolerant accessions with RRG% of > 52% were observed in 5.4% of the total accessions. A selection index calculated based on all root traits in acid soil screening was highest in AGG70137 (636.7) whereas it was lowest in Precoz (76.3). All histochemical and biochemical analyses supported the hydroponic results as Northfield, AGG70137, AGG70561 and AGG70281 showed consistent good performance. The identified new sources of Al tolerant lentil germplasm can be used to breed new Al toxicity tolerant lentil varieties. The established high throughput hydroponic method can be routinely used for screening lentil breeding populations for Al toxicity tolerance. Future recommendations could include evaluation of the yield potential of the selected subset of accessions under acid soil field conditions, and the screening of a wider range of landrace accessions originating from areas with Al toxic acid soils.

Despite the ability of mangrove trees to allocate a large proportion of the total biomass to the underground roots, little is known about the benthic macrofauna–root system relationships. We evaluated the above- and belowground structures of plants, soil properties, algal cover and their relationship with macrofauna as a function of soil strata (0–2.5, 2.5–5 and 5–10 cm) and distance (0–0.30 and 3–3.5 m) from trunks in three mangrove sites in southern Brazil. Coarse root biomass was higher near the trunks and in shallower layers, while fine root biomass predominated far from trunks and indifferent to the soil stratum. The macrofauna was more associated with changes in the root systems than with other soil properties. Most of the benthic taxa occurred in the upper layers of the soil (0–2.5 cm) and near trunks (< 0.30 m), where there was a lower proportion of fine roots. Fine root entanglement inhibited the presence of organisms with more complex body plans, which may hamper their locomotion and feeding activities. Therefore, the structure and function of macrofauna varied according to the depth stratum and distance from the trunks.

The ecological study of root systems lags behind the understanding of the aboveground components of plant communities, mainly due to methodological challenges. As ecological root theory develops complexity, root investigation methods are required to meet higher standards of quantitative and detailed data. Spatial root density distribution of plants represents one of the main features pursued in ecological studies, as it provides insight into root foraging behavior and belowground competition. To study root density, ecologists should preferably use and develop methods with the potential to provide the most comprehensive information: Individual Root Density Distribution (IRDD), i.e. individual-level and spatially-explicit root density maps. Here, we review the existing methods to detect roots in the field (detection methods), and to infer the identity of these roots (identification methods). We discuss potential combinations of Detection and Identification (DI) methods, and the data quality that these combinations yield in respect to IRDD. We anticipate that root field ecologists progressively may want to adopt DI methods showing the highest potential to provide high-quality IRDD. These methods are (i) ground-penetrating radar or acoustic tomography in combination with tracking the roots to the individual plant (i.e. skeleton method sensu lato), (ii) soil sampling in combination with in situ root staining (for physiological individuals), or (iii) soil sampling in combination with DNA microsatellites or single nucleotide polymorphism sequencing (for genetic individuals).

Organic mulching is an effective forest management technique that improves the soil environment and promotes plant growth. The rhizosphere is an important interface connecting root systems and soil. However, the rhizosphere effects (REs) after organic mulching are still unknown. We conducted a field experiment in a 15-year-old Ligustrum lucidum forest of urban greening space. Changes in REs on carbon and nitrogen fractions, enzyme activity after organic mulching were measured, and their relationships with fine-root traits and soil properties were analysed. Organic mulching reduced or inverted REs for most enzyme activities and carbon and nitrogen fractions but only significantly decreased the positive REs for urease activities and weakened the negative REs for peroxidase activities. Furthermore, more enzymes were affected over time, and more organic mulch application had greater effects. Seasons affected REs more than organic mulching; seasons contributed more to changes in fine-root traits and soil properties. REs on biotic factors (microbial biomass carbon, microbial biomass nitrogen, urease, and peroxidase activities), which are more sensitive than other soil carbon and nitrogen fractions we measured, were primarily related to fine-root traits (specific root length, specific surface area, and carbon and nitrogen content) and soil properties (temperature, water content, and bulk density). Organic mulching masks the REs on most soil carbon and nitrogen fractions, as well as on enzyme activities, and the REs on enzyme activities are more sensitive. Understanding the variation in REs will improve our knowledge of element cycling between soil and plants.

Morphological assessment of arbuscular mycorrhizal (AM) fungal diversity in rhizosphere soils may not reflect the AM fungal species colonizing the roots. Recently, DNA-based molecular approaches offer a wide range of advantages in understanding the AM fungal abundance both in soil and root systems. In this study, the community composition of native AM fungi in the soil and roots of aromatic black rice (Oryza sativa L. cv. Chakhao amubi) during the flowering stage in the terrace farming system was evaluated. AM fungal spore density ranged between 72 and 110 spores per 100 g shade-dried soil and varied significantly with rice terraces. All examined root fragments were colonized by AM fungi. However, the root length containing different AM fungal structures did not vary significantly compared to total root length colonization. The genomic DNA from rice roots was amplified with AM fungal specific primers using nested PCR and sequenced thereafter. Results of 18S rDNA partial region sequences revealed the presence of seven AM fungal species in roots, whereas in rhizosphere soils ten AM fungal spore morphotypes were recorded. Such dissimilarity in species richness of AMF between rhizosphere soil and the roots implied that some indigenous AMF species were adapted to specific soil environments that could colonize the paddy crop roots and suggests that the conditions can be suitable for some AMF species which have an important function in traditional terrace rice cultivation of hilly tracts in North-East India.

This study investigated maize-soil biota interactions as well as the soil legacy effects of continuous monoculture (CM) on maize performance. We conducted a glasshouse experiment that compared the performance of maize inoculated with living or sterilized soil inocula collected from experimental field plots with cropping histories of 1 to 5 years of continuous maize monoculture, where the soil type is Nicollet clay loam with moderate fertility. We measured the biomass, yield, root traits and leaf nutrients of maize as well as eukaryotic soil organisms. Inoculation with living soil dramatically reduced maize biomass and yield compared to inoculation with sterilized soil, showing CM to have strong negative soil biotic legacy effects on maize. Nonetheless, the strength of soil biotic effects on most maize variables were relatively stable over time under CM. The response of maize total biomass to living soil inoculation correlated positively with arbuscular mycorrhizal (AM) fungal abundance but negatively with soil fauna abundance, whereas it did not relate with the abundance of plant pathogenetic fungi or herbivorous nematodes. The roots showed acquisitive syndromes (high specific root length but low root diameter) in sterilized soil but conservative syndromes (opposite traits) in living soil. The responses in root system structure were tightly related with AM fungal diversity and community composition. Our study shows strong and stable negative effects of soil biota on maize under CM. The complex effects of soil biota on maize performance highlight the need to explore the functions of different groups of soil organisms to better understand and control negative soil legacy effects in agroecosystems.

Non-mycorrhizal species such as Banksia (Proteaceae) that depend on root exudates to acquire phosphorus (P) are prominent in south-western Australia, a biodiversity hotspot on severely P-impoverished soils. We investigated the consequences of an exudate-releasing P-mobilising strategy related to control of iron (Fe) acquisition in two Banksia species, B. attenuata R.Br. and B. laricina C. Gardner, that differ greatly in their geographical distribution and rarity. We undertook solution culture experiments to measure root-mediated Fe reduction (FeR) in non-cluster and cluster roots at four stages of cluster-root development, and whole root systems for plants grown at 2 to 300 μM Fe (as Fe-EDTA). As a positive control, we used Pisum sativum (cv. Dunn) to validate the FeR assay. Unlike typical Strategy I species, both Banksia species showed no significant variation in FeR, for either cluster or non-cluster roots, when grown at a wide range of Fe supply. For roots of different developmental stages, we measured a range for B. attenuata cluster roots of 0.13 ± 0.03 to 1.29 ± 0.14 μmol Fe3+ reduced g−1 FW h−1 and 0.56 ± 0.11 to 1.10 ± 0.24 μmol Fe3+ reduced g−1 FW h−1 in non-cluster roots. Similarly, for B. laricina cluster-roots, FeR ranged from 0.22 ± 0.07 to 1.21 ± 0.37 μmol Fe3+ reduced g−1 FW h−1, and in non-cluster roots from 0.56 ± 0.11 to 0.71 ± 0.08 μmol Fe3+ reduced g−1 FW h−1. We also observed only minor differences for whole-root system FeR, and even though B. attenuata showed signs of leaf Fe deficiency in the 2 μM Fe treatment, its FeR was the lowest of both species across all treatments at 0.079 ± 0.009 μmol Fe3+ reduced g−1 FW h−1, compared with the fastest rate of 0.20 ± 0.014 μmol Fe3+ reduced g−1 FW h−1 for B. laricina in the 28 μM Fe treatment. Taking plants through a pulse from low to high Fe, then back to low Fe supply did not elucidate any significant response in FeR. Although Fe acquisition is tightly controlled in the investigated Banksia species, such control is not based on regulation of FeR, which challenges the model that is commonly accepted for Strategy I species.

Soil water uptake is a function of root growth and distribution. Therefore, restrictions on root system growth may reduce water and nutrient uptake, which results in slower plant growth. The objective of this study was to determine the effects of different irrigation strategies, nitrogen application rates, and planting methods on the winter wheat root growth. The experimental factors included two irrigation strategies (variable alternate furrow irrigation defined as partial root-zone irrigation and ordinary furrow irrigation), two planting methods (in-furrow planting and on-ridge planting), and three nitrogen (N) application rates (0, 150, and 300 kg N ha−1) in 2015–2016 and 2016–2017 growing seasons. Results indicated that the in-furrow planting decreased mean root length density and root mass density (8% and 10%, respectively, in the fertilized treatments) compared to that obtained in the on-ridge planting. The partial root-zone irrigation reduced root length density by about 5% and 7% in the fertilized treatments compared to that obtained in full irrigation in the first and second year, respectively; however, these reductions were not statistically significant. Furthermore, the results implied that nitrogen fertilizer application increased root length density by 48% and 24% in the first and second year, respectively. Likely, root mass density increased by 32% and 5% in the first and second year, respectively. The exponential decaying relationship between root length density and soil depth indicated that the in-furrow planting with 300 kg N ha −1 produced the highest root density at the soil surface layer and reduced deep root penetration compared to the on-ridge planting and the other N treatments. Further analysis revealed that grain yield linearly correlated with root length density and root mass density in the first year. However, a polynomial (quadratic) relationship was obtained in the second year. Consequently, increasing the main root traits, including root length and root mass, enhanced winter wheat grain yield until it reached a threshold value. Higher values negatively affected grain yield, which might be due to allocating carbon to roots instead of grains.

The present work was initiated in order to test whether the growth and pathogenic behavior of fungal isolates infecting Faba bean (FB) are influenced by salt and drought stress. A collection of 108 fungal isolates was recovered from different infected FB plants grown in various bioclimatic zones in Tunisia. Koch’s postulates revealed that 54% of those isolates caused root rots infection by 25% to 100% of the whole root system. Eighteen pathogenic fungal isolates were chosen based on their high incidence on various plant growth parameters using the heat map analysis to undergo the in vitro analysis, where 13 isolates belong to Fusarium spp. The in vitro mycelial growth of the 18 strains in potato-dextrose agar amended with NaCl and PEG6000 was strain dependent, in which F. equiseti (VFF12, VFF16), F. graminearum VFF6, F. brachygibbosum VFF9, Alternaria sp. VFF5, Boeremia exigua VFF4, Rutstroemia sp. VFF7 and Rhizopus oryzae VFF1 showed a significant increase by up to 150% compared to controls. Best linear unbiased predictors (BLUPs) for differences in root and shoot dry weights between control (inoculated unstressed plants) and inoculated under salt and drought stress of the tolerant fungal strains were analyzed. BLUPs of VFF16, VFF6, and VFF7 were significantly increased under both stresses compared to controls. While, BLUBs of VFF12, VFF9, and VFF4 were not significant, which maintained similar pathogenic effect. However, BLUPs of VFF5 and VFF1 were significantly decreased. Consequently, soil salinization and water deficiency - occurring nowadays in many parts of the world - can increase the aggressiveness of phytopathogenic fungi.

Plants grown in stony soils have better developed root systems and higher crop yields. The roles of physical and chemical effects of stony soils on plant growth have been published, but the roles of soil microbiota have not been investigated. In this study, Tetrastigma hemsleyanum plants were cultivated for 2 years in stony soils and the same soils after removing rock fragments (non-stony soils). The composition of bacterial community and the tuber transcriptome were analyzed, using multiple bioinformatics methods. Compared with non-stony soils, stony soils supported a significantly different bacterial community, which was associated with larger tuber size of T. hemsleyanum. Stony soils had greater bacterial diversity, co-occurrence network complexity, and greater abundance of bacterial taxa belonging to Actinobacteria, Rokubacteria, Rhizobiales, Desulfarculaceae, and Chthoniobacteraceae than the corresponding microbiota in non-stony soils. The differential soil bacterial communities between stony and non-stony soils may be mainly driven by soil physicochemical properties, such as available S, organic matter, and pH. The discriminatory bacterial taxa of soils shaped the bacterial communities of rhizosphere soil, and tuber surface soil (TS), which was strongly correlated with tuber size parameters. In addition, the potential functions of the discriminatory bacterial taxa in TS corresponded closely with gene pathways of the host, like phytohormone biosynthesis, photosynthesis, and biotic stress resistance, which are crucial for the initiation and development of tubers. These results not only help us to better understand the role of stony soils in improving plant growth but also provide a reference for increasing tuber yield through the use of microbial inocula.

Coffee production in agroforestry systems (AFS) is known as a tool for mitigating climate change. Although, there are allometric models to estimate aboveground biomass of coffee bushes (Coffea arabica L.), allometric models for estimating its belowground components have not been developed yet. In this study, models as a function of easy measurable variables, like stem diameter at 15 cm height (D15), and total height (h) were developed. A total of 40 coffee plants that grow in the four main production systems in the municipality of Libano, Tolima, Colombia: (1) monoculture; (2) AFS with plantain (Musa AAB); (3) AFS with laurel (Cordia alliodora); and (4) organic, were sampled. Standing bushes were measured (D15 and h), cut at ground level, and their root systems (diameter > 2 mm) were hand-extracted. Both above and belowground biomass (AGB and BGB, respectively) were gravimetrically estimated, as well as the root to shoot ratio (R:S) was estimated. Correlation analysis between dependent and independent variables were performed, and generic models with linear and transformed variables were tested. D15 ranged from 0.6 to 8.0 cm, and h from 0.46 to 3.0 m with a total BGB ranging from 10 g to 2.3 kg/plant. A R:S of 0.49 was estimated with no effect on cultivars and production systems. The best biomass model was BGB = 0.096 + 0.022 * D152; where BGB: total belowground biomass (kg/plant); D15 (cm); RMSE = 0.30. A model for estimating BGB based on AGB was also developed. These tools allow a highly accurate measuring of the BGB of coffee bushes in the production systems for a research or a carbon credits project.