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Tamarix ramosissima has an important role in stabilizing sand dunes in desert ecosystems. Understanding the water use strategies of T. ramosissima is essential to understand its adaptations on coppice dunes. We utilized the stable isotopes δ2H and δ18O in soil water, groundwater, and xylem water to identify monthly differences in water sources. Additionally. we explored rooting depth using 2H2O as an artificial tracer. In May, T. ramosissima derived 75% of its water from shallow and middle soil layers. In July, it absorbed 90% water from middle and deep soil layers. In August and September, it acquired approximately 80% of its water from deep soil layers. The labelling using 2H as an artificial tracer indicated that the root system of T. ramosissima could reach depths >500 cm in the coppice dunes. 2H absorption was observed at depths of 100, 200, 300 and 400 cm. Soil water is the dominant water source for T. ramosissima in the coppice dunes because groundwater is at depths >30 m. The flexible water-use strategies of T. ramosissima enable it to effectively utilize different available water sources to adapt to the arid environment. These findings improve our understanding of water uptake patterns and drought adaptation strategies of T. ramosissima in the coppice dunes of desert ecosystems.

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Plant water uptake from the soil is a crucial element of the global hydrological cycle and essential for vegetation drought resilience. Yet, knowledge of how the distribution of water uptake depth (WUD) varies across species, climates, and seasons is scarce relative to our knowledge of aboveground plant functions. With a global literature review, we found that average WUD varied more among biomes than plant functional types (i.e. deciduous/evergreen broadleaves and conifers), illustrating the importance of the hydroclimate, especially precipitation seasonality, on WUD. By combining records of rooting depth with WUD, we observed a consistently deeper maximum rooting depth than WUD with the largest differences in arid regions - indicating that deep taproots act as lifelines while not contributing to the majority of water uptake. The most ubiquitous observation across the literature was that woody plants switch water sources to soil layers with the highest water availability within short timescales. Hence, seasonal shifts to deep soil layers occur across the globe when shallow soils are drying out, allowing continued transpiration and hydraulic safety. While there are still significant gaps in our understanding of WUD, the consistency across global ecosystems allows integration of existing knowledge into the next generation of vegetation process models.

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Root architectural phenotypes are promising targets for crop breeding, but root architectural effects on microbial associations in agricultural fields are not well understood. Architecture determines the location of microbial associations within root systems, which, when integrated with soil vertical gradients, determines the functions and the metabolic capability of rhizosphere microbial communities. We argue that variation in root architecture in crops has important implications for root exudation, microbial recruitment and function, and the decomposition and fate of root tissues and exudates. Recent research has shown that the root microbiome changes along root axes and among root classes, that root tips have a unique microbiome, and that root exudates change within the root system depending on soil physicochemical conditions. Although fresh exudates are produced in larger amounts in root tips, the rhizosphere of mature root segments also plays a role in influencing soil vertical gradients. We argue that more research is needed to understand specific root phenotypes that structure microbial associations and discuss candidate root phenotypes that may determine the location of microbial hotspots within root systems with relevance to agricultural systems.

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Exploring plant root characteristics is important to understand the aboveground plant growth and ecosystem, but has rarely been conducted because of the difficulties in obtaining root information. This study aims to clarify the root distribution and rooting strategy under the combined control of vegetation types and rainfall gradients. We compiled 64 plant root and 81 soil water profiles up to 10 m deep with plant ages of up to 40 years old in China's Loess Plateau, and then fitted the shape and extinction coefficients (ß) and proposed the relation of D95/D50 (ratio of depth corresponding to 95 % of total biomass to that corresponding to 50 % of total biomass) to ß to characterize the rooting strategy. The cumulative root biomass increase from shallow- to deep-rooted plants, and from >550 mm to <450 mm precipitation gradients. The root system parameters have large spatial variability, dominated by vegetation type but supplemented by climate. The negative correlation between D95/D50 and ß indicated a tradeoff between rooting depths and root biomass. The plants would change rooting strategy from increasing root biomass to increasing rooting depths when the plant stand age and soil water depletion degree are >25.7 ± 3.6 years and 35.7 % ± 15.1 %, respectively. These results reveal a clear plant rooting strategy that extends root deeper rather than increases root biomass triggered by critical age and soil water depletion.

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Experiments often find that net primary productivity (NPP) increases with species richness when native species are considered. However, relationships may be altered by exotic (non-native) species, which are hypothesized to reduce richness but increase productivity (i.e., 'invasion-diversity-productivity paradox'). We compared richness-NPP relationships using a comparison of exotic versus native-dominated sites across the central USA, and two experiments under common environments. Aboveground NPP was measured using peak biomass clipping in all three studies, and belowground NPP was measured in one study with root ingrowth cores using root-free soil. In all studies, there was a significantly positive relationship between NPP and richness across native species-dominated sites and plots, but no relationship across exotic-dominated ones. These results indicate that relationships between NPP and richness depend on whether native or exotic species are dominant, and that exotic species are 'breaking the rules', altering richness-productivity and richness-C stock relationships after invasion.

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The distribution of roots throughout the soil drives depth-dependent plant-soil interactions and ecosystem processes, particularly in arctic tundra where plant biomass, is predominantly belowground. Vegetation is usually classified from aboveground, but it is unclear whether such classifications are suitable to estimate belowground attributes and their consequences, such as rooting depth distribution and its influence on carbon cycling. We performed a meta-analysis of 55 published arctic rooting depth profiles, testing for differences both between distributions based on aboveground vegetation types (Graminoid, Wetland, Erect-shrub, and Prostrate-shrub tundra) and between 'Root Profile Types' for which we defined three representative and contrasting clusters. We further analyzed potential impacts of these different rooting depth distributions on rhizosphere priming-induced carbon losses from tundra soils. Rooting depth distribution hardly differed between aboveground vegetation types but varied between Root Profile Types. Accordingly, modelled priming-induced carbon emissions were similar between aboveground vegetation types when they were applied to the entire tundra, but ranged from 7.2 to 17.6 Pg C cumulative emissions until 2100 between individual Root Profile Types. Variations in rooting depth distribution are important for the circumpolar tundra carbon-climate feedback but can currently not be inferred adequately from aboveground vegetation type classifications.

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Savannas cover a significant fraction of the Earth's land surface. In these ecosystems, C3 trees and C4 grasses coexist persistently, but the mechanisms explaining coexistence remain subject to debate. Different quantitative models have been proposed to explain coexistence, but these models make widely contrasting assumptions about which mechanisms are responsible for savanna persistence. Here, we show that no single existing model fully captures all key elements required to explain tree-grass coexistence across savanna rainfall gradients, but many models make important contributions. We show that recent empirical work allows us to combine many existing elements with new ideas to arrive at a synthesis that combines elements of two dominant frameworks: Walter's two-layer model and demographic bottlenecks. We propose that functional rooting separation is necessary for coexistence and is the crux of the coexistence problem. It is both well-supported empirically and necessary for tree persistence, given the comprehensive grass superiority for soil moisture acquisition. We argue that eventual tree dominance through shading is precluded by ecohydrological constraints in dry savannas and by fire and herbivores in wet savannas. Strong asymmetric grass-tree competition for soil moisture limits tree growth, exposing trees to persistent demographic bottlenecks.

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Plant litter decomposition is a key ecosystem process in carbon and nutrient cycling, and is heavily affected by changing climate. While the direct effects of drought on decomposition are widely studied, in order to better predict the overall drought effect, indirect effects associated with various drought-induced changes in ecosystems should also be quantified. We studied the effect of an extreme (5-month) experimental drought on decomposition, and if this effect varies with two dominant perennial grasses, plant parts (leaves vs. roots), and soil depths (0-5 cm vs. 10-15 cm) in a semi-arid temperate grassland. After 12 months, the average litter mass loss was 43.5% in the control plots, while only 25.7% in the drought plots. Overall, mass loss was greater for leaves (44.3%) compared to roots (24.9%), and for Festuca vaginata (38.6%) compared to Stipa borysthenica (30.5%). This variation was consistent with the observed differences in nitrogen and lignin content between plant parts and species. Mass loss was greater for deep soil (42.8%) than for shallow soil (26.4%). Collectively, these differences in decomposition between the two species, plant parts, and soil depths were similar in magnitude to direct drought effect. Drought induces multiple changes in ecosystems, and our results highlight that these changes may in turn modify decomposition. We conclude that for a reliable estimate of decomposition rates in an altered climate, not only direct but also indirect climatic effects should be considered, such as those arising from changing species dominance, root-to-shoot ratio, and rooting depth.

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Potato is one of the most important vegetable crops worldwide. Its growth, development and ultimately yield is hindered by drought stress condition. Breeding and selection of deep-rooted and drought-tolerant potato varieties has become a prime approach for improving the yield and quality of potato (Solanum tuberosum L.) in arid and semiarid areas. A comprehensive understanding of root development-related genes has enabled scientists to formulate strategies to incorporate them into breeding to improve complex agronomic traits and provide opportunities for the development of stress tolerant germplasm. Root response to drought stress is an intricate process regulated through complex transcriptional regulatory network. To understand the rooting depth and molecular mechanism, regulating root response to drought stress in potato, transcriptome dynamics of roots at different stages of drought stress were analyzed in deep (C119) and shallow-rooted (C16) cultivars. Stage-specific expression was observed for a significant proportion of genes in each cultivar and it was inferred that as compared to C16 (shallow-rooted), approximately half of the genes were differentially expressed in deep-rooted cultivar (C119). In C16 and C119, 11 and 14 coexpressed gene modules, respectively, were significantly associated with physiological traits under drought stress. In a comparative analysis, some modules were different between the two cultivars and were associated with differential response to specific drought stress stage. Transcriptional regulatory networks were constructed, and key components determining rooting depth were identified. Through the results, we found that rooting depth (shallow vs deep) was largely determined by plant-type, cell wall organization or biogenesis, hemicellulose metabolic process, and polysaccharide metabolic process. In addition, candidate genes responding to drought stress were identified in deep (C119) and shallow (C16) rooted potato varieties. The results of this study will be a valuable source for further investigations on the role of candidate gene(s) that affect rooting depth and drought tolerance mechanisms in potato.

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Droughts exarcerbate Plant-soil feedbacks (PSFs) making positive PSFs more positive and negative PSFs more negative. Alterations in PSFs that droughts induce could relate to the rooting depth of the tested plants. We present some rare evidence on how a driver of global change will alter a biotic interaction.

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The efficient uptake of nutrients depends on the ability of roots to respond to gradients of these resources. Although pot experiments have shown that species differ in their ability to proliferate their roots in nutrient-rich patches, the role of such differences in determining root shapes in the field is unclear. We used fine-scale quantitative (q)PCR-based species-specific mapping of roots in a grassland community to reconstruct species-specific root system shapes. We linked them with data from pot experiments on the ability of these species to proliferate in nutrient-rich patches and their rooting depth. We found remarkable diversity in root system shapes, from cylindrical to conical. Interspecific differences in rooting depths in pots were the main determinant of rooting depths in the field, whereas differences in foraging ability played only a minor role. Although some species with strong foraging ability did place their roots into nutrient-rich soil layers, it was not a universal pattern. The results imply that although the vertical differentiation of grassland species is pronounced, it is primarily not driven by the differential plastic response of species to soil nutrient gradients. This may constrain the coexistence of species with similar rooting depths and may instead favour coexistence of species differing in their architectural blueprints.

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Although the above and belowground sizes and shapes of plants strongly influence plant competition, community structure, and plant-environment interactions, plant sizes and shapes remain poorly characterized across climate regimes. We investigated relationships among shoot and root system size and climate. We assembled and analyzed, to our knowledge, the largest global database describing the maximum rooting depth, lateral spread, and shoot size of terrestrial plants - more than doubling the Root Systems of Individual Plants database to 5647 observations. Water availability and growth form greatly influence shoot size, and rooting depth is primarily influenced by temperature seasonality. Shoot size is the strongest predictor of lateral spread, with root system diameter being two times wider than shoot width on average for woody plants. Shoot size covaries strongly with rooting system size; however, the geometries of plants differ considerably across climates, with woody plants in more arid climates having shorter shoots, but deeper, narrower root systems. Additionally, estimates of the depth and lateral spread of plant root systems are likely underestimated at the global scale.

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Understanding the soil-to-plant transfer process of 137Cs is essential for predicting the contamination levels of plants in contaminated areas. The rooting depth is considered one of the key factors explaining the difference in the activity concentration of 137Cs in different plant species. In this study, the distributions of 137Cs and 133Cs in soils and plants were investigated, and the plants' rooting depth of 137Cs uptake was estimated using the 137Cs/133Cs ratios in exchangeable fractions of soils and biological samples. The results showed that different plant species accumulate different levels of 137Cs and 133Cs. The 137Cs/133Cs ratios were fairly constant in plants of the same species. The average 137Cs/133Cs ratios in bamboo grasses and ferns were 0.015 ± 0.009 (n = 5) and 0.13 ± 0.04 Bq ng-1 (n = 10) in Yamakiya, respectively. The percentage of 137Cs in the exchangeable fraction of the uppermost soil layer was lower than that in the deeper soil layers. The activity concentrations of 137Cs in the soil profiles decreased sharply with depth, whereas the depth distributions of 133Cs were uniform. Therefore, the 137Cs/133Cs ratios were driven mainly by the 137Cs activity concentrations in soil. The plants' rooting depths of 137Cs uptake were estimated on the basis of the relationships between the averaged 137Cs/133Cs ratio in the soil layer and the 137Cs/133Cs ratio in the plant. The results indicate that the deeper-rooted species such as bamboo grasses have a lower accumulation of 137Cs than the superficial-rooting species such as ferns. The soil-to-plant transfer factors would be determined using rooting depth by calculating the averaged activity concentration of 137Cs within the estimated rooting depth.

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Increasing severity and frequency of drought is predicted for large portions of the terrestrial biosphere, with major impacts already documented in wet tropical forests. Using a 4-year rainfall exclusion experiment in the Daintree Rainforest in northeast Australia, we examined canopy tree responses to reduced precipitation and soil water availability by quantifying seasonal changes in plant hydraulic and carbon traits for 11 tree species between control and drought treatments. Even with reduced soil volumetric water content in the upper 1 m of soil in the drought treatment, we found no significant difference between treatments for predawn and midday leaf water potential, photosynthesis, stomatal conductance, foliar stable carbon isotope composition, leaf mass per area, turgor loss point, xylem vessel anatomy, or leaf and stem nonstructural carbohydrates. While empirical measurements of aboveground traits revealed homeostatic maintenance of plant water status and traits in response to reduced soil moisture, modeled belowground dynamics revealed that trees in the drought treatment shifted the depth from which water was acquired to deeper soil layers. These findings reveal that belowground acclimation of tree water uptake depth may buffer tropical rainforests from more severe droughts that may arise in future with climate change.

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Selection for root system architectures (RSA) to match target growing environments can improve yields through better adaptation to water and nutrient-limiting conditions in grain legume crops such as mungbean. In this study, the architectural development of root systems in four contrasting mungbean varieties was studied over time to explore their relationships to above-ground growth and development. Key findings suggested that early maturing mungbean varieties were characterized by more rapid root elongation rates and leaf area development, resulting in more vigorous root and shoot growth during early growth stages compared with a late maturing variety. The early maturing varieties also showed root morphological traits generally adapted to water-limited environments, such as deeper, longer and lighter roots. Early maturing varieties more rapidly colonized the top 10-20 cm of the soil profile during early growth stages, whereas the later maturing variety developed less prolific but 20-50% thicker roots in the same profile layers in later stages of crop growth. The diversity of root characteristics identified in these commercial varieties suggests that there are opportunities to combine desirable root traits with maturity types to target different production environments. Examples include deeper, longer, and thinner roots for crops to exploit deep profile reserves of water and nutrients, and thicker and shallower root systems for crops grown in shallow soils with stratified nutrient reserves and/or more favorable in-season rainfall.

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Deciduous shrubs are expanding across the graminoid-dominated nutrient-poor arctic tundra. Absorptive root traits of shrubs are key determinants of nutrient acquisition strategy from tundra soils, but the variations of shrub root traits within and among common shrub genera across the arctic climatic gradient are not well resolved. Consequently, the impacts of arctic shrub expansion on belowground nutrient cycling remain largely unclear. Here, we collected roots from 170 plots of three commonly distributed shrub genera (Alnus, Betula, and Salix) and a widespread sedge (Eriophorum vaginatum) along a climatic gradient in northern Alaska. Absorptive root traits that are relevant to the strategy of plant nutrient acquisition were determined. The influence of aboveground dominant vegetation cover on the standing root biomass, root productivity, vertical rooting profile, as well as the soil nitrogen (N) pool in the active soil layer was examined. We found consistent root trait variation among arctic plant genera along the sampling transect. Alnus and Betula had relatively thicker and less branched, but more frequently ectomycorrhizal colonized absorptive roots than Salix, suggesting complementarity between root efficiency and ectomycorrhizal dependence among the co-existing shrubs. Shrub-dominated plots tended to have more productive absorptive roots than sedge-dominated plots. At the northern sites, deep absorptive roots (>20 cm depth) were more frequent in birch-dominated plots. We also found shrub roots extensively proliferated into the adjacent sedge-dominated plots. The soil N pool in the active layer generally decreased from south to north but did not vary among plots dominated by different shrub or sedge genera. Our results reveal diverse nutrient acquisition strategies and belowground impacts among different arctic shrubs, suggesting that further identifying the specific shrub genera in the tundra landscape will ultimately provide better predictions of belowground dynamics across the changing arctic.

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Root architecture is a promising breeding target for developing resource-efficient crops. Breeders and plant physiologists have called for root ideotypes that have narrow, deep root systems for improved water and nitrate capture, or wide, shallower root systems for better uptake of less mobile topsoil nutrients such as phosphorus. Yet evidence of relationships between root architecture and crop yield is limited. Many studies focus on the response to a single constraint, despite the fact that crops are frequently exposed to multiple soil constraints. For example, in dryland soils under no-till management, topsoil nutrient stratification is an emergent profile characteristic, leading to spatial separation of water and nutrients as the soil profile dries. This results in spatio-temporal trade-offs between efficient resource capture and pre-defined root ideotypes developed to counter a single constraint. We believe there is need to identify and better understand trade-offs involved in the efficient capture of multiple, spatially disjunct soil resources. Additionally, how these trade-offs interact with genotype (root architecture), environment (soil constraints), and management (agronomy) are critical unknowns. We argue that identifying root traits that enable efficient capture of multiple soil resources under fluctuating environmental constraints is a key step towards meeting the challenges of global food security.

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