Depth Of Water Uptake Research Articles

Water fluxes mediated by vegetation: emerging isotopic insights at the soil and atmosphere interfaces.

Plants mediate water fluxes within the soil-vegetation-atmosphere continuum. This water transfer in soils, through plants, into the atmosphere can be effectively traced by stable isotopologues of water. However, rapid dynamic processes have only recently gained attention, such as adaptations in root water uptake depths (within hours to days) or the imprint of transpirational fluxes on atmospheric moisture, particularly promoted by the development of real-time in-situ water vapour stable isotope observation techniques. We focus on open questions and emerging insights at the soil-plant and plant-atmosphere interfaces, as we believe that these are the controlling factors for ecosystem water cycling. At both interfaces, complex pictures of interacting ecophysiological and hydrological processes emerge: root water uptake dynamics depend on both spatiotemporal variations in water availability and species-specific regulation of adaptive root conductivity within the rooting system by, for example, modulating soil-root conductivity in response to water and nutrient demands. Similarly, plant water transport and losses are a fine-tuned interplay between species-specific structural and functional strategies of water use and atmospheric processes. We propose that only by explicitly merging insights from distinct disciplines - for example, hydrology, plant physiology and atmospheric sciences - will we gain a holistic picture of the impact of vegetation on processes governing the soil-plant-atmosphere continuum.

Species‐specific differences in water uptake depth of mature temperate trees vary with water availability in the soil

Temperate tree species differ in their physiological sensitivity to declining soil moisture and drought. Although species-specific responses to drought have often been suggested to be the result of different water uptake depths, empirical evidence for such a mechanism is scarce. Here we test if differences in water uptake depths can explain previously observed species-specific physiological responses of temperate trees to drought and if the water uptake depth of different species varies in response to declining soil moisture. For this purpose, we employed stable oxygen and hydrogen isotopes of soil and xylem water that we collected over the course of three growing seasons in a mature temperate forest in Switzerland. Our data show that all investigated species utilise water from shallow soil layers during times of sufficient soil water supply. However, Fraxinus excelsior, Fagus sylvatica and Acer pseudoplatanus were able to shift their water uptake to deeper soil layers when soil water availability decreased in the topsoil. In contrast, Picea abies, was not able to shift its water uptake to deeper soil layers. We conclude from our data that more drought-resistant tree species are able to shift their water uptake to deeper soil layers when water availability in the topsoil is becoming scarce. In addition, we were able to show that water uptake depth of temperate tree species is a trait with high plasticity that needs to be characterised across a range of environmental conditions.

Prolonged warming and drought modify belowground interactions for water among coexisting plants.

Understanding how climate alters plant-soil water dynamics, and its impact on physiological functions, is critical to improved predictions of vegetation responses to climate change. Here we analyzed how belowground interactions for water shift under warming and drought, and associated impacts on plant functions. In a semi-arid woodland, adult trees (piñon and juniper) and perennial grasses (blue grama) were exposed to warming and precipitation reduction. After 6 years of continuous treatment exposure, soil and plant water isotopic composition was measured to assess plant water uptake depths and community-level water source partitioning. Warming and drought modified plant water uptake depths. Under warming, contrasting changes in water sources between grasses and trees reduced belowground water source partitioning, resulting in higher interspecific competition for water. Under drought, shifts in trees and grass water sources to deeper soil layers resulted in the maintenance of the naturally occurring water source partitioning among species. Trees showed higher water stress, and reduced water use and photosynthesis in response to warming and drought. This case study demonstrates that neighboring plants shift their competitive interactions for water under prolonged warming and drought, but regardless of whether changes in moisture sources will result in increased competition among species or maintained partitioning of water resources, these competitive adaptations may easily be overridden by climate extremes.

Examination of deep root water uptake using anomalies of soil water stable isotopes, depth-controlled isotopic labeling and mixing models

Knowledge on the water uptake depths of vegetation is crucial for understanding water transport processes of the soil-vegetation atmosphere continuum and relevant for many applications (e.g. the estimation of groundwater recharge, irrigation planning and the parameterization of (eco-) hydrological models). The identification and quantification of water uptake from deep soil layers and groundwater remain challenging. This study uses a combined framework based on natural abundances of stable water isotopes and isotopic labeling experiments with deuterium oxide (2H2O) to study root water uptake and identify uptake from deep soil in a semi-arid environment.Between 2013 and 2016, more than 1000 soil (isotope depth profiles); plant (xylem and transpiration) and water (precipitation and groundwater) samples for the analysis of isotope ratios were collected. Two experiments using isotopic labeling were carried out in order to assess root water uptake depths. Herein, we i) present series of deep soil water isotope depth profiles, interpret water transport dynamics and ecohydrological feedbacks; ii) examine the suitability of natural isotope depth profiles for identifying deep root water uptake; iii) apply the Bayesian mixing model MixSIAR to quantify deep root water uptake and iv) constrain water uptake depths using isotopic labeling experiments and derive an active root water uptake distribution.Our results show that the form of isotope depth profiles of soil in water-limited environments follows characteristic shapes for the end of the rainy and dry seasons, respectively. Isotope ratios in the upper 4 m of the soil are heavily dependent on the character of the respective rainy season. Under certain conditions – e.g. droughts or weak rainy seasons – the isotope depth profile displays an enrichment in heavy isotopes up to 4 m depth. Such pronounced anomalies provide an opportunity for studies on source water partitioning. In the present experiment, the studied individuals of Acacia erioloba were found to obtain 37% [24–52%] of their water from deep soil (>4 m) and groundwater at the end of the dry season of 2015. All other investigated trees (individuals of B. plurijuga, S. luebertii, T. sericea and C. collinum) mainly utilize water originating from 1 m to 2.5 m depth. Under “average” rainy season conditions, the similarity of isotope ratios of potential plant water sources hinders a conclusive identification of water uptake depths.Deep natural isotope depth profiles in dry environments can – under certain conditions – be used to identify and quantify access of vegetation to deep water resources. Isotopic labeling enables to determine active root distributions for the lateral root zone. Combined frameworks contribute to a better understanding of deep water uptake. A differentiated consideration of water uptake from the lateral root zone and deep, potentially groundwater-tapping roots is required in order to fully investigate ecohydrological feedbacks and for a proper parameterization of models.

Plant species richness and functional groups have different effects on soil water content in a decade‐long grassland experiment

Abstract The temporal and spatial dynamics of soil water are closely interlinked with terrestrial ecosystems functioning. The interaction between plant community properties such as species composition and richness and soil water mirrors fundamental ecological processes determining above‐ground–below‐ground feedbacks. Plant–water relations and water stress have attracted considerable attention in biodiversity experiments. Yet, although soil scientific research suggests an influence of ecosystem productivity on soil hydraulic properties, temporal changes of the soil water content and soil hydraulic properties remain largely understudied in biodiversity experiments. Thus, insights on how plant diversity—productivity relationships affect soil water are lacking. Here, we determine which factors related to plant community composition (species and functional group richness, presence of plant functional groups) and soil (organic carbon concentration) affect soil water in a long‐term grassland biodiversity experiment (The Jena Experiment). Both plant species richness and the presence of particular functional groups affected soil water content, while functional group richness played no role. The effect of species richness changed from positive to negative and expanded to deeper soil with time. Shortly after establishment, increased topsoil water content was related to higher leaf area index in species‐rich plots, which enhanced shading. In later years, higher species richness increased topsoil organic carbon, likely improving soil aggregation. Improved aggregation, in turn, dried topsoils in species‐rich plots due to faster drainage of rainwater. Functional groups affected soil water distribution, likely due to plant traits affecting root water uptake depths, shading, or water‐use efficiency. For instance, topsoils in plots containing grasses were generally drier, while plots with legumes were moister. Synthesis. Our decade‐long experiment reveals that the maturation of grasslands changes the effects of plant richness from influencing soil water content through shading effects to altering soil physical characteristics in addition to modification of water uptake depth. Functional groups affected the soil water distribution by characteristic shifts of root water uptake depth, but did not enhance exploitation of the overall soil water storage. Our results reconcile previous seemingly contradictory results on the relation between grassland species diversity and soil moisture and highlight the role of vegetation composition for soil processes.

Groundwater drawdown drives ecophysiological adjustments of woody vegetation in a semi-arid coastal ecosystem.

Predicted droughts and anthropogenic water use will increase groundwater lowering rates and intensify groundwater limitation, particularly for Mediterranean semi-arid ecosystems. These hydrological changes may be expected to elicit differential functional responses of vegetation either belowground or aboveground. Yet, our ability to predict the impacts of groundwater changes on these ecosystems is still poor. Thus, we sought to better understand the impact of falling water table on the physiology of woody vegetation. We specifically ask (a) how is woody vegetation ecophysiological performance affected by water table depth during the dry season? and (b) does the vegetation response to increasing depth to groundwater differ among water-use functional types? We examined a suite of physiological parameters and water-uptake depths of the dominant, functionally distinct woody vegetation along a water-table depth gradient in a Mediterranean semi-arid coastal ecosystem that is currently experiencing anthropogenic groundwater extraction pressure. We found that groundwater drawdown did negatively affect the ecophysiological performance of the woody vegetation. Across all studied environmental factors, depth to groundwater was the most important driver of ecophysiological adjustments. Plant functional types, independent of groundwater dependence, showed consistent declines in water content and generally reduced C and N acquisition with increasing depths to groundwater. Functional types showed distinct operating physiological ranges, but common physiological sensitivity to greater water table depth. Thus, although differences in water-source use exist, a physiological convergence appeared to happen among different functional types. These results strongly suggest that hydrological drought has an important impact on fundamental physiological processes, constraining the performance of woody vegetation under semi-arid conditions. By disentangling the functional responses and vulnerability of woody vegetation to groundwater limitation, our study establishes the basis for predicting the physiological responses of woody vegetation in semi-arid coastal ecosystems to groundwater drawdown.

Water consumption by an agroecosystem with shelter forests of corn and Populus in the North China Plain

Shelter forests play a significant role in farmland protection and the improvement of microclimates in the North China Plain, but controversy persists over the water relationship between shelter forest and crops. To explore whether the introduction of a protective forest aggravates the water stress of crops, we used stable isotopes to investigating the water sources of corn and its Populus shelter forest. The Penman–Monteith Model and the thermal dissipation probe methods were used to explore the evapotranspiration (ET) of a cornfield with shelter forest (CN) and a cornfield with no shelter forest (CK). The results suggested that corn and Populus exhibited considerable plasticity in depth of water uptake. Although there was no significant difference in water sources of corn between CN and CK, the corn and its shelter forest appeared to have relatively complementary water use patterns. The corn predominantly absorbed water from depths of 0–10 cm (23.4–46.7%), 10–20 cm (33.3–35.8%), and 20–40 cm (20.9–26.3%) during the early growth stages, and it then altered its water sources to depths of 10–20 cm (22.3–24.7%), 20–40 cm (23.7–28.1%), and 40–60 cm (25.7–39.0%) near the of its growth stages. However, Populus mainly obtained water from depths of 40–60 cm (19.8–24.1%), 60–80 cm (24.6–26.9%), and >80 cm (27.3–30.8%) throughout the growing season. The total ET of CN was 6.6% less than that of the CK due to the impact of the microclimate. The ET of CN was primarily from the cornfield, and to a lesser extent, from Populus shelter forest. Our results indicated that the introduction of Populus shelter forest does not increase water stress on corn, and it can reduce regional water resource consumption. For rational utilization of water resources, it would be feasible to select a reasonable arrangement of tree species to develop the Populus shelter forest compound system near corn farmlands in the North China Plain.

Reduced dry season transpiration is coupled with shallow soil water use in tropical montane forest trees.

Tropical montane cloud forests (TMCF) are ecosystems particularly sensitive to climate change; however, the effects of warmer and drier conditions on TMCF ecohydrology remain poorly understood. To investigate functional responses of TMCF trees to reduced water availability, we conducted a study during the 2014 dry season in the lower altitudinal limit of TMCF in central Veracruz, Mexico. Temporal variations of transpiration, depth of water uptake and tree water sources were examined for three dominant, brevi-deciduous species using micrometeorological, sap flow and soil moisture measurements, in combination with oxygen and hydrogen stable isotope composition of rainfall, tree xylem, soil and stream water. Over the course of the dry season, reductions in crown conductance and transpiration were observed in canopy species (43 and 34%, respectively) and mid-story trees (23 and 8%), as atmospheric demand increased and soil moisture decreased. Canopy species consistently showed more depleted isotope values compared to mid-story trees. However, MixSIAR Bayesian model results showed that the evaporated (enriched) soil water pool was the main source for trees despite reduced soil moisture. Additionally, while increases in tree water uptake from deeper to shallower soil water sources occurred, concomitant decreases in transpiration were observed as the dry season progressed. A larger reduction in deep soil water use was observed for canopy species (from 79 ± 19 to 24 ± 20%) compared to mid-story trees (from 12 ± 17 to 10 ± 12%). The increase in shallower soil water sources may reflect a trade-off between water and nutrient requirements in this forest.

Water utilization characteristics of typical vegetation in the rocky mountain area of Beijing, China

Seasonal drought are expected to occur more frequent and intense in the some regions due to global climate change, which may significantly influence in the competitive interactions of water uptake depth for vegetation communities. We investigated the impacts of seasonal drought on water utilization for vegetation communities using hydrogen-2 and oxygen-18 stable isotope techniques in Beijing rocky mountainous area. Our results indicate that the water sources of the four plant species varied by season. Platycladus orientalis largely absorbed water from middle (31.5% in May and 35.9% in November) and deep (32.8% in May and 38.4% in November) soil layers during the dry season and switched its main water source to surface layers (50.3% in July and 37.2% in September) during the wet season. Contrary to P. orientalis, Quercus variabilis mainly absorbed water from surface and middle soil layers during the dry season and changed its dominant water sources to the deep soil layer throughout the wet season; at same time, this species utilized water from natural springs in July and the middle soil layer in September. V. negundo var. heterophylla mostly utilized water from deep soil layers (38.7%) in May and transferred its main water source to surface (43.5%) and middle (33.1%) layers in July. This species primarily utilized water from surface (29.2%) and middle (30.8%) soil layers in September, and from middle (35.4%) and deep (27.8%) layers in November, similar to the findings of P. orientalis in this season. In contrast the above three plant species, C. heterophylla Fisch mainly absorbed water from surface and middle soil layers throughout the year, having very little reliance on water from deep soil layers. P. orientalis and Q. variabilis showed the opposite characteristics of water utilization, which suggests that these two species are suitable for a mixed forest vegetation when selecting plant species for afforestation. However, since the water sources of P. orientalis and V. negundo var. heterophylla were from similar soil depths, there may be potential competition for moisture between these two species. Our findings provide an indication as to which vegetation species are suitable to grow together when undertaking restoration in drought prone environments.

A simple greenhouse experiment to explore the effect of cryogenic water extraction for tracing plant source water

AbstractStable isotopes of water (2H and 18O) are useful tracers for determining root water uptake depths. In such studies, plant and soil water are extracted most commonly by cryogenic vacuum distillation. However, recent studies have suggested that cryogenic extraction conditions (extraction time, temperature, and vacuum) and soil physicochemical properties affect the isotopic composition of extracted soil water. Here, we perform a simple greenhouse trial with 2 plant species (Taraxacum officinale and Pelargonium spp.) in 2 soil types (clayey loam and sand) to test our ability to match plant water to its putative soil water source(s) by using different extraction conditions (30–240 min, 80–200 °C, 0.1 Pa). We irrigated plants with water of known isotopic composition, sampled root crowns and soils at 2 depths, and varied the cryogenic water extraction conditions.Our isotope results from the sandy soils were unaffected by cryogenic extraction conditions. In contrast, extraction parameters affected the isotope composition of waters recovered from clayey soil. This influenced the estimates of plant water sourcing, where δ2H and δ18O returned different results from each other. With higher extraction temperatures and longer extraction times, we gradually extracted more enriched soil water, which reflected the source water of both plant species. Our results imply that longer extraction times and temperatures for clayey soils are needed to reduce fractionation effects during the extraction procedure. Future studies should explore how these effects apply to natural clay‐rich soils as well as plant tissue isotope composition.

Comparisons of the Performance of δ13C and δ18O of Fagus sylvatica, Pinus sylvestris, and Quercus petraea in the Record of Past Climate Variations

AbstractClimate reconstructions in temperate Europe have been widely based on oak species. However, other co‐occurring species, largely distributed in Europe, may be used for recording climate variability. In this paper, we documented the intertrees and interspecies variations over 1960–2007 of oxygen and carbon isotopic compositions in ring cellulose of Fagus sylvatica, Pinus sylvestris, and Quercus petraea co‐occurring in the Fontainebleau forest (France). Our results indicated that large levels of series replication (11 trees on average) were required to generate isotopic mean series representative of the populations. We calculated mean isotopic ratios higher in pine than in the deciduous species and hypothesized that these contrasts resulted from differences in stomatal conductance, phenology, and canopy structure and, for oxygen, also in water uptake depth and isotopic exchange rate. We found that δ18O and δ13C chronologies were significantly correlated to one another in the three species and responded primarily to air moisture and Tmax, which indicated that stomatal conductance was an important driver of changes in both types of records. We determined that the correlations were strong with the May to July climate variables in F. sylvatica and with the July and August ones in Q. petraea and P. sylvestris. We showed that the oxygen records were systematically more coherent than those of carbon. This study demonstrated that δ18O, and to a lesser extent δ13C, from the three different species are reliable proxies for reconstructing past hydroclimatic variations in Europe.

The roots of the drought: Hydrology and water uptake strategies mediate forest‐wide demographic response to precipitation

Abstract Drought‐induced tree mortality is expected to increase globally due to climate change, with profound implications for forest composition, function and global climate feedbacks. How drought is experienced by different species is thought to depend fundamentally on where they access water vertically below‐ground, but this remains untracked so far due to the difficulty of measuring water availability at depths at which plants access water (few to several tens of metres), the broad temporal scales at which droughts at those depths unfold (seasonal to decadal), and the difficulty in linking these patterns to forest‐wide species‐specific demographic responses. We address this problem through a new eco‐hydrological framework: we used a hydrological model to estimate below‐ground water availability by depth over a period of two decades that included a multi‐year drought. Given this water availability scenario and 20 year long‐records of species‐specific growth patterns, we inversely estimated the relative depths at which 12 common species in the forest accessed water via a model of water stress. Finally, we tested whether our estimates of species relative uptake depths predicted mortality in the multi‐year drought. The hydrological model revealed clear below‐ground niches as precipitation was decoupled from water availability by depth at multi‐annual scale. Species partitioned the hydrological niche by diverging in their uptake depths and so in the same forest stand, different species experienced very different drought patterns, resulting in clear differences in species‐specific growth. Finally, species relative water uptake depths predicted species mortality patterns after the multi‐year drought. Species that our method ranked as relying on deeper water were the ones that had suffered from greater mortality, as the zone from which they access water took longer to recharge after depletion. Synthesis. This research changes our understanding of how hydrological niches operate for trees, with a trade‐off between realized growth potential and survival under drought with decadal scale return time. The eco‐hydrological framework highlights the importance of species‐specific below‐ground strategies in predicting forest response to drought. Applying this framework more broadly may help us better understand species coexistence in diverse forest communities and improve mechanistic predictions of forests productivity and compositional change under future climate.

Analyzing root traits to characterize juniper expansion into rangelands

Juniper expansion into sagebrush-dominated communities is a phenomenon occurring across large regions of the western U.S. in the past century. We investigated the competitive abilities for belowground resources of Juniperus osteosperma (Utah juniper) and Artemisia tridentata (big sagebrush) based on fine root traits and spatial patterns of water uptake inferred from stem and soil stable oxygen isotopes (δ18O). Data were collected from neighboring J. osteosperma and A. tridentata plants in northern Colorado and included measurements of different size classes of J. osteosperma: short (<30 cm), intermediate (30 cm–3 m), and tall (>3 m). Short J. osteosperma switched from utilizing shallow to primarily deep water sources across the growing season. Artemisia tridentata had root traits associated with faster root proliferation and resource acquisition (significantly greater specific root length and smaller root diameter, p < .01), but greater J. osteosperma fine root biomass (p < .01) resulted in similar root length densities between the two species at most soil depths (p > .1). Additionally, we found that short J. osteosperma individuals can quickly develop deep root systems, but there is little difference in belowground foraging between individuals of J. osteosperma and A. tridentata based on the depth of water uptake and root length density.

基于双稳定同位素和MixSIAR模型的冬小麦根系吸水来源研究

PDF HTML阅读 XML下载 导出引用 引用提醒 基于双稳定同位素和MixSIAR模型的冬小麦根系吸水来源研究 DOI: 10.5846/stxb201802250384 作者: 作者单位: 中国地质大学(北京),中国科学院地理科学与资源研究所,中国地质大学(北京),中国地质大学(北京),中国水利水电科学研究院,中国地质大学(北京),中国科学院生态环境研究中心 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41671027，41730749） Applying dual stable isotopes and a MixSIAR model to determine root water uptake of winter wheat Author: Affiliation: School of Water Resources and Environment,China University of Geosciences Beijing,Key Laboratory of Water Cycle and Related Land Surface Processes,Institute of Geographic Sciences and Natural Resources Research,Chinese Academy of Sciences,School of Water Resources and Environment,China University of Geosciences Beijing,School of Water Resources and Environment,China University of Geosciences Beijing,State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin,China Institute of Water Resources and Hydropower Research,School of Water Resources and Environment,China University of Geosciences Beijing,State Key Laboratory of Urban and Regional Ecology Research Center for Eco-Environmental Sciences,Chinese Academy of Sciences Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:灌溉和施肥措施对农田水文循环具有重要影响，根系吸水是联系植物蒸腾和土壤水分运动的关键水文过程，定量识别灌溉施肥影响下作物根系吸水来源对农业用水优化管理具有重要意义。氘氧稳定同位素（D和18O）是追溯农田水分运移过程的理想天然示踪剂。基于2013-2015年北京市典型农田不同灌溉施肥处理冬小麦水分运移试验，利用D和18O双稳定同位素和MixSIAR贝叶斯混合模型，量化冬小麦主要根系吸水深度及其贡献比例，阐明作物水分来源的季节变化及不同处理间的差异，分析根系吸水与土壤水分分布变化的相互关系。研究结果表明：两季冬小麦返青-拔节、拔节-抽穗、抽穗-灌浆和灌浆-收获期主要根系吸水深度均值分别为0-20 cm（67.0%）、20-70 cm（42.0%）、0-20 cm（38.7%）和20-70 cm（34.9%），但季节变化差异显著，2014季主要吸水深度随作物的生长发育而逐渐增加，2015季则主要集中于浅层土壤（0-70 cm）。返青-抽穗期仅灌水20 mm或施肥105 kg/hm2 N促使拔节-抽穗期深层（70-200 cm）土壤水分利用率平均增加29%，而前期充分灌水且大量施肥（≥当地施肥量210 kg hm-2 N）时拔节-抽穗期根系吸水深度为土壤表层0-20 cm。在干旱少雨的冬小麦生长季内作物吸水来源与土壤水分消耗变化基本一致。 Abstract:Irrigation and fertilization scheduling significantly affect field water cycles. Root water uptake is the critical process that connects plant transpiration and soil water movements. It is necessary to quantify the crop water uptake sources under different irrigation and fertilization treatments for optimizing agricultural water management. The stable water isotopes of D and 18O are considered as ideal (natural) tracers for tracking water through the soil based on distinct isotopic signatures of water fluxes. The MixSIAR framework is the latest Bayesian stable isotope analysis mixing model in R that considers multiple sources of uncertainty and provides definite proportions of source contributions. In this study, dual stable isotopes of soil water and stem water were applied to determine seasonal water uptake patterns of winter wheat under different irrigation and fertilization treatments during 2013-2015 in Beijing, China. The contributions of the soil water at each depth to water uptake were quantified using the MixSIAR Bayesian mixing model. The direct inference method was also used to detect the potential root water uptake depth. Correlations between the water uptake patterns and soil moisture changes were further evaluated. The average contribution of soil water in the 0-20, 20-70, 70-150, and 150-200 cm layers was 35.6%, 27.6%, 23.1%, and 13.7%, respectively. The primary root water uptake depth was 0-20 cm (67.0%), 20-70 cm (42.0%), 0-20 cm (38.7%), and 20-70 cm (34.9%) during the greening-jointing, jointing-heading, heading-filling, and filling-harvest periods, respectively. Significant differences in crop water use appeared between the 2014 and 2015 growing seasons. The main root water uptake depth gradually increased from 0-20 cm (greening-jointing period) to 70-150 cm (heading-filling period) and was maintained at the 70-150 cm depth until the filling-harvest period in the 2014 season. However, winter wheat mainly took up soil water from the shallow layers (0-70 cm) over the 2015 season. In particular, the proportional soil water contribution in the 0-20 cm layer was remarkably higher (13.9%) than that in the 2014 season. Root water uptake patterns with soil moisture distributions were significantly influenced by different irrigation and fertilization treatments, especially in dry seasons. The main water uptake source was the soil water in the top layer (0-20 cm) under the T4 and T5 treatments during the jointing-heading period in 2015, because the root growth in the surface layer was stimulated by sufficient irrigation (80 mm) and abundant fertilization (≥ 210 kg/hm2 N) at early growth stages. Nitrogen deficiency with < 105 kg/hm2 N (T3) or less irrigation with 20 mm (T1 and T2) during the greening-jointing period promoted root growth in the deep soil layer (70-200 cm) and increased water adsorption by a mean of 29% during the jointing-filling period. Seasonal variations in the quantitative contribution of soil water at different depths were closely related to the soil moisture distributions. The large contribution of soil water in the 0-150 cm layer (86.3%) was consistent with its proportional consumption in soil water storage (92%) throughout the greening to harvest season of winter wheat. This study provides a simple and effective method for identifying crop water sources. The findings are of great significance for future fertilization and irrigation management. 参考文献 相似文献 引证文献

Water use by broadleaved tree species in response to changes in precipitation in a mountainous area of Beijing

Extreme weather events are expected to occur more frequently in the future, which may influence water distribution and uptake patterns in rocky mountainous areas of North China. To examine how plants respond and adapt to the extreme environment, we investigated water sources of the broadleaved tree species Quercus variabilis under a precipitation gradient (A: no natural precipitation, B: half of natural precipitation, C: natural precipitation, and D: twice the natural precipitation) using the stable isotope approach in the Beijing mountainous area. The results indicated that Q. variabilis exhibited considerable plasticity in the depth of water uptake and showed a strong dependence on deeper soil layers under the precipitation gradient. Q. variabilis mainly absorbed water from the 0–20cm (20.02–28.61%) and 60–80cm (22.81–29.44%) soil layers, and also used groundwater (26.32–30.54%) under the low soil water conditions of the A treatment. In the B treatment, Q. variabilis absorbed water from the groundwater (29.60–33.53%) and 60–80cm (26.05–29.44%) soil layers and a small amount of water from 0 to 20cm (10.67–12.25%). In the C and D treatments, the soil water content was greater than that of the B treatment; Q. variabilis still predominantly absorbed water from the 60–80cm (26.88% and 27.35%, respectively) soil layer and groundwater (33.52% and 46.17%, respectively), and took minimal water from the 0–20cm and 20–40cm soil layers. We found that Q. variabilis showed no obvious responses to precipitation under the precipitation gradient, and its dimorphic root system allowed it to uptake different water sources under drought and humid environmental conditions and thus maintain its transpiration. Therefore, we can infer that Q. variabilis is well adapted to extreme precipitation events and has a strong adaptability to both extreme drought and flood conditions.

Hydrologic regulation of plant rooting depth

Plant rooting depth affects ecosystem resilience to environmental stress such as drought. Deep roots connect deep soil/groundwater to the atmosphere, thus influencing the hydrologic cycle and climate. Deep roots enhance bedrock weathering, thus regulating the long-term carbon cycle. However, we know little about how deep roots go and why. Here, we present a global synthesis of 2,200 root observations of >1,000 species along biotic (life form, genus) and abiotic (precipitation, soil, drainage) gradients. Results reveal strong sensitivities of rooting depth to local soil water profiles determined by precipitation infiltration depth from the top (reflecting climate and soil), and groundwater table depth from below (reflecting topography-driven land drainage). In well-drained uplands, rooting depth follows infiltration depth; in waterlogged lowlands, roots stay shallow, avoiding oxygen stress below the water table; in between, high productivity and drought can send roots many meters down to the groundwater capillary fringe. This framework explains the contrasting rooting depths observed under the same climate for the same species but at distinct topographic positions. We assess the global significance of these hydrologic mechanisms by estimating root water-uptake depths using an inverse model, based on observed productivity and atmosphere, at 30″ (∼1-km) global grids to capture the topography critical to soil hydrology. The resulting patterns of plant rooting depth bear a strong topographic and hydrologic signature at landscape to global scales. They underscore a fundamental plant-water feedback pathway that may be critical to understanding plant-mediated global change.

Increasing carbon discrimination rates and depth of water uptake favor the growth of Mediterranean evergreen trees inthe ecotone with temperate deciduous forests.

Tree populations at the low-altitudinal or -latitudinal limits of species' distributional ranges are predicted to retreat toward higher altitudes and latitudes to track the ongoing changes in climate. Studies have focused on the climatic sensitivity of the retreating species, whereas little is known about the potential replacements. Competition between tree species in forest ecotones will likely be strongly influenced by the ecophysiological responses to heat and drought. We used tree-ring widths and δ13 C and δ18 O chronologies to compare the growth rates and long-term ecophysiological responses to climate in the temperate-Mediterranean ecotone formed by the deciduous Fagus sylvatica and the evergreen Quercus ilex at the low altitudinal and southern latitudinal limit of F. sylvatica (NE Iberian Peninsula). F. sylvatica growth rates were similar to those of other southern populations and were surprisingly not higher than those of Q. ilex, which were an order of magnitude higher than those in nearby drier sites. Higher Q. ilex growth rates were associated with high temperatures, which have increased carbon discrimination rates in the last 25 years. In contrast, stomatal regulation in F. sylvatica was proportional to the increase in atmospheric CO2 . Tree-ring δ18 O for both species were mostly correlated with δ18 O in the source water. In contrast to many previous studies, relative humidity was not negatively correlated with tree-ring δ18 O but had a positive effect on Q. ilex tree-ring δ18 O. Furthermore, tree-ring δ18 O decreased in Q. ilex over time. The sensitivity of Q. ilex to climate likely reflects the uptake of deep water that allowed it to benefit from the effect of CO2 fertilization, in contrast to the water-limited F. sylvatica. Consequently, Q. ilex is a strong competitor at sites currently dominated by F. sylvatica and could be favored by increasingly warmer conditions.

Quantification of dynamic soil–vegetation feedbacks following an isotopically labelled precipitation pulse

Abstract. The presence of vegetation alters hydrological cycles of ecosystems. Complex plant–soil interactions govern the fate of precipitation input and water transitions through ecosystem compartments. Disentangling these interactions is a major challenge in the field of ecohydrology and a pivotal foundation for understanding the carbon cycle of semi-arid ecosystems. Stable water isotopes can be used in this context as tracer to quantify water movement through soil–vegetation–atmosphere interfaces. The aim of this study is to disentangle vegetation effects on soil water infiltration and distribution as well as dynamics of soil evaporation and grassland water use in a Mediterranean cork oak woodland during dry conditions. An irrigation experiment using δ18O labelled water was carried out in order to quantify distinct effects of tree and herbaceous vegetation on the infiltration and distribution of event water in the soil profile. Dynamic responses of soil and herbaceous vegetation fluxes to precipitation regarding event water use, water uptake depth plasticity, and contribution to ecosystem soil evaporation and transpiration were quantified. Total water loss to the atmosphere from bare soil was as high as from vegetated soil, utilizing large amounts of unproductive evaporation for transpiration, but infiltration rates decreased. No adjustments of main root water uptake depth to changes in water availability could be observed during the experiment. This forces understorey plants to compete with adjacent trees for water in deeper soil layers at the onset of summer. Thus, understorey plants are subjected to chronic water deficits faster, leading to premature senescence at the onset of drought. Despite this water competition, the presence of cork oak trees fosters infiltration and reduces evapotranspirative water losses from the understorey and the soil, both due to altered microclimatic conditions under crown shading. This study highlights complex soil–plant–atmosphere and inter-species interactions controlling rain pulse transitions through a typical Mediterranean savannah ecosystem, disentangled by the use of stable water isotopes.

Tree soil water uptake and transpiration in mono-cultural and jungle rubber stands of Sumatra

Rubber tree mono-cultural plantations are expanding. Also, there is an increasing search for ‘green’ rubber production. Rubber tree cultivation in stands with admixed, spontaneously established native trees, referred to as jungle rubber, has a long tradition on Sumatra. For rubber tree monocultures on mainland Asia, concerns have been raised because of potentially very high tree transpiration rates. The objectives of our study were to analyze tree water use rates and tree soil water uptake depths in mono-cultural and jungle rubber stands with a focus on the role of tree diameter. Sap flux measurements suggest similar water use rates for rubber trees in the two cultivation systems. Stand-level transpiration in jungle rubber was 27% higher than in rubber monocultures, which was related to higher stand densities in jungle rubber stands. A water stable isotope (δ18O and δD) approach suggests different soil water uptake depths for the rubber trees in the two cultivation systems. In a relatively dry period, the main tree water uptake in the monoculture was relatively close to the soil surface, whereas rubber trees in jungle rubber stands mainly took up water from deeper soil strata; here the native trees had their main uptake depth relatively close to the soil surface. This pattern indicates plasticity in rubber tree water uptake and points to competitive displacement. Across rubber trees in both cultivation systems and also among the native trees, there was a clear relationship between tree diameter and soil water uptake depth: bigger trees tended to take up soil water closer to the soil surface. Diameter and density regulation by thinning of big native trees thus appears as a potential management option for influencing water uptake in jungle rubber stands in favor of rubber trees.

Methods to estimate changes in soil water for phenotyping root activity in the field

Background and aimsThere is an urgent need to develop new high throughput approaches to phenotype roots in the field. Excavating roots to make direct measurements is labour intensive. An alternative to excavation is to measure soil drying profiles and to infer root activity.MethodsWe grew 23 lines of wheat in 2013, 2014 and 2015. In each year we estimated soil water profiles with electrical resistance tomography (ERT), electromagnetic inductance (EMI), penetrometer measurements and measurements of soil water content. We determined the relationships between the measured variable and soil water content and matric potential.ResultsWe found that ERT and penetrometer measurements were closely related to soil matric potential and produced the best discrimination between wheat lines. We found genotypic differences in depth of water uptake in soil water profiles and in the extent of surface drying.ConclusionsPenetrometer measurements can provide a reliable approach to comparing soil drying profiles by different wheat lines, and genotypic rankings are repeatable across years. EMI, which is more sensitive to soil water content than matric potential, and is less effective in drier soils than the penetrometer or ERT, nevertheless can be used to rapidly screen large populations for differences in root activity.