Water Uptake Dynamics Research Articles

Spatio-temporal dynamics of root water uptake and identification of soil moisture thresholds for precision irrigation in a Mediterranean yellow-fleshed kiwifruit orchard

Spatio-temporal dynamics of root water uptake and identification of soil moisture thresholds for precision irrigation in a Mediterranean yellow-fleshed kiwifruit orchard

Drought effects in Mediterranean forests are not alleviated by diversity‐driven water source partitioning

Abstract Tree species diversity in forest ecosystems could reduce their vulnerability to extreme droughts through improved microclimate and below‐ground water source partitioning driven by contrasting species‐specific water use patterns. However, little is known about the seasonal dynamics of belowground water uptake that determine whether diversity positively or negatively impacts tree carbon assimilation and water exchange. Using a network of 30 permanent plots in Mediterranean forests with increasing tree species diversity (from monospecific to four‐species mixtures), we examined the seasonal patterns of in‐situ aboveground carbon and water relations and belowground water sources on 265 trees from four pine and oak species over 2 years using hydraulic and stable isotope approaches. We found that increasing species diversity in broadleaf and conifer mixtures induced strong soil water source partitioning between oak and pine species. As conditions became drier during the summer in mixed stands, oak species took up water from deeper soil sources, while pines were systematically limited to shallow ones. Despite significant belowground moisture partitioning, stronger drought‐induced reductions in photosynthesis, stomatal conductance, and leaf water potential were still observed in diverse compared with monospecific stands for pines but with some benefits for oaks. Synthesis: Our findings reveal that tree species diversity promoted belowground water source partitioning in mixed oak and pine stands, potentially reducing competition for water in more diverse ecosystems. Yet, our results show that it is insufficient to buffer the adverse impacts of severe droughts on aboveground tree carbon and water use, leading to higher water stress, especially for pines.

Simulating Tree Root Water Uptake in the Frame of Sustainable Agriculture for Extreme Hyper-Arid Environments Using Modeling and Geophysical Techniques

In order to ensure sustainability in the agricultural sector and to meet global food needs, a particularly important challenge for our time is to investigate the possibility of increasing agricultural production in areas with extreme hyper-arid environments. Warming air temperatures and sandy soils significantly influence tree root water uptake (RWU) dynamics, making accurate estimation of RWU depth distribution and magnitude crucial for effective resource management, particularly in the context of precision irrigation within agroecosystems. This study employed two non-invasive techniques, namely HYDRUS 1D and electrical resistivity tomography (ERT), to simulate RWU under controlled experimental conditions and under an extreme hyper-arid environment. The results revealed that the highest RWU rates occurred during the morning (08:00–11:00). RWU activity predominantly concentrated in the upper soil profile (0–30 cm), and the soil water content in this area was notably lower compared to the deeper soil layers. With increasing temperature, there was a tendency for the RWU zone to shift to lower depths within the soil profile. The findings of this study could have important implications for farmers, providing valuable insights to implement irrigation water management strategies.

Root Distribution and Water Uptake Applied by Hydrogen and Oxygen Stable Isotopes for Lianas in Northwest China

The root distribution and water uptake of irrigated vines (Vitis vinifera L.) in arid oasis areas remain poorly understood, particularly in terms of the variations in water uptake resulting from plant type and growing period. In this study, excavation and soil coring were employed to investigate the root distribution of vines. Meanwhile, the water uptake dynamics of irrigated vines in an arid oasis area were developed using stable isotopes of hydrogen and oxygen in water bodies (δD and δ18O) and in crops and soil water, coupled with a direct inference approach and a linear mixed model (IsoSource). The soil layers were divided into nine layers via hierarchical cluster analysis. The results indicated that the vertical distributions of the total and fine roots of grapevines were mainly in the range of 40–160 cm, accounting for 93.1% (91.2%) and 92.5% (90.0%) of the total root (200 cm) distribution during May and October, respectively. In the horizontal direction, both the total root and fine root systems were mainly distributed within 0–100 cm from the trunk and contributed 81.2% and 79.8% of the total root distribution, respectively. Meanwhile, both the total root weight (length) density and fine root weight (length) density decreased gradually with increasing radial distance from the trunk in the 0–80 cm range. The main water uptake of vines was at 0–40 cm in June, 20–80 cm in July, and 40–100 cm in August. These findings suggest that the main depth of root water uptake increases during the whole growth stage for grapevines in arid oasis ecosystems. This information will help growers to improve irrigation efficiency and provide a data analysis of water conservation in an arid oasis area during water stress.

A chemo-mechanical model for describing sorption hysteresis in a glassy polyurethane

Hysteretic sorption and desorption of water is observed from 0 to 95% relative humidity and 298–333 K on a glassy polyurethane foam. It is postulated that sorption-induced swelling of the glassy polyurethane increases the concentration of accessible hydrogen-bonding adsorption sites for water. The accessibility of sites is kinetically controlled due to the restricted thermal motions of chains in the glassy polymer, causing a difference in accessible site concentrations during sorption and desorption. This discrepancy leads to hysteresis in the sorbed concentrations of water. A coupled chemo-mechanical model relating volumetric strain, adsorption site concentration, and sorbed water concentration is employed to describe water sorption hysteresis in the glassy polyurethane. This model not only describes the final mass uptake for each relative humidity step, but also captures the dynamics of water uptake, which exhibit diffusion and relaxation rate-controlled regimes.

Interaction between beech and spruce trees in temperate forests affects water use, root water uptake pattern and canopy structure.

Beneficial and negative effects of species interactions can strongly influence water fluxes in forest ecosystems. However, little is known about how trees dynamically adjust their water use when growing with interspecific neighbours. Therefore, we investigated the interaction effects between Fagus sylvatica (European beech) and Picea abies (Norway spruce) on water-use strategies and aboveground structural characteristics. We used continuous in situ isotope spectroscopy of xylem and soil water to investigate source water dynamics and root water uptake depths. Picea abies exhibited a reduced sun-exposed crown area in equally mixed compared with spruce-dominated sites, which was further correlated to a reduction in sap flow of -14.5±8.2%. Contrarily, F. sylvatica trees showed +13.3±33.3% higher water fluxes in equally mixed compared with beech-dominated forest sites. Although a significantly higher crown interference by neighbouring trees was observed, no correlation of water fluxes and crown structure was found. High time-resolved xylem δ2H values showed a large plasticity of tree water use (-74.1 to -28.5‰), reflecting the δ2H dynamics of soil and especially precipitation water sources. Fagus sylvatica in equally mixed sites shifted water uptake to deeper soil layers, while uptake of fresh precipitation was faster in beech-dominated sites. Our continuous in situ water stable isotope measurements traced root water uptake dynamics at unprecedented temporal resolution, indicating highly dynamic use of water sources in response to precipitation and to neighbouring species competition. Understanding this plasticity may be highly relevant in the context of increasing water scarcity and precipitation variability under climate change.

Bark water uptake through lenticels increases stem hydration and contributes to stem swelling.

Foliar water uptake can recharge water storage tissue and enable greater hydration than through access to soil water alone; however, few studies have explored the role of the bark in facilitating water uptake. We investigated pathways and dynamics of bark water uptake (BWU) in stems of the mangrove Avicennia marina. We provide novel evidence that specific entry points control dynamics of water uptake through the outer bark surface. Furthermore, using a fluorescent symplastic tracer dye we provide the first evidence that lenticels on the outer bark surface facilitate BWU, thus increasing stem water content by up to 3.7%. X-ray micro-computed tomography showed that BWU was sufficient to cause measurable swelling of stem tissue layers increasing whole stem cross-sectional area by 0.83 mm2 or 2.8%, implicating it as a contributor to the diel patterns of water storage recharge that buffer xylem water potential and maintain hydration of living tissue.

Estimating uptake and internal transport dynamics of irrigation water in apple trees using deuterium-enriched water

With future climatic scenarios foreseeing increased crop water demands and reduced irrigation water availability, a deeper knowledge on the dynamics of water uptake and translocation inside plants is needed. Little is known about the time interval existing between the irrigation water supply and the presence of irrigation water inside trees, and whether the dripper localization can affect water uptake and translocation dynamics. Another research gap concerns the redistribution of irrigation water in the canopy following irrigation localized to one side of the tree.A field and a pot experiment were designed to gain more insight into this context. In the field experiment, we tested the effect of different drip irrigation layouts on the extent and velocity of water uptake by apple trees. Trees were irrigated using deuterium-enriched water using one, two, or four drippers per tree. Samples were collected from different heights in the canopy at regular intervals following the irrigation event. In the pot experiment, the soil was saturated with labelled water and samples were collected at different time intervals and heights along the tree stem. Labelled water was detected in the lowest stem section of potted trees after 1 h from irrigation. In field-grown trees, labelled water appeared in the shoots after 4 h and 6 h in the bottom and top part of the canopy, respectively. By increasing the number of drippers per tree, the fraction of irrigation water in the shoots increased accordingly. However, uptake and transport velocity were unaffected by the number of drippers, averaging 0.60–0.65 m h-1. In trees that were irrigated from one side only, irrigation water could be found on the opposite side in the top part of the canopy. Our results suggest that the localization and amount of irrigation water can significantly influence root water uptake in apple trees.

Impact of biochar amendments on soil water and plant uptake dynamics under different cropping systems

AbstractApplication of biochar amendments in agricultural systems has received much attention in recent years. In this study, we assess the 5‐year impacts of biochar application on soil water and plant interactions for an irrigated fresh market tomato (Solanum lycopersicum) and a rainfed pasture (Poaceae) cropping system. In particular, we focus on three varieties of locally produced biochar from agricultural waste materials—almond shell, walnut shell, and almond pruning residues that are pyrolyzed using a mobile pyrolysis unit. We used the soil hydrological model HYDRUS‐1D to explicitly track seasonal and annual soil water fluxes through changes in water retention, drainage, evaporation, and plant water uptake under biochar application. Modeling results show that the application of biochar at 5% increased soil water availability within the top 20 cm for a rainfed system, irrespective of biochar amendment type. This is clearly indicative of higher plant water uptake and greater water use efficiency (WUE) under biochar application. In contrast, a similar biochar amendment for the irrigated system did not affect WUE, instead reducing seasonal soil evaporation loss and thereby reducing irrigation demand. In both cropping systems, year‐to‐year variability in precipitation significantly impacted the total amount of water saved under biochar application with certain amendments retaining more water than others. Given that biochar application increased water retention irrespective of cropping systems, we further used a simple approach to determine yield trade‐off, if any, between control and biochar treatments. Our economic balance clearly demonstrates that the water saved by amending soil with biochar does not offset the yield disparity if compensated with carbon credits and therefore, application of biochar should be actively considered for both its direct and indirect benefits to potential greenhouse gas mitigation (e.g., diverting orchard waste from open burning), water savings, and soil health.

Deep roots mitigate drought impacts on tropical trees despite limited quantitative contribution to transpiration

Deep rooting is considered a central drought-mitigation trait with vast impact on ecosystem water cycling. Despite its importance, little is known about the overall quantitative water use via deep roots and dynamic shifts of water uptake depths with changing ambient conditions. Knowledge is especially sparse for tropical trees. Therefore, we conducted a drought, deep soil water labeling and re-wetting experiment at Biosphere 2 Tropical Rainforest. We used in situ methods to determine water stable isotope values in soil and tree water in high temporal resolution. Complemented by soil and stem water content and sap flow measurements we determined percentages and quantities of deep-water in total root water uptake dynamics of different tree species. All canopy trees had access to deep-water (max. uptake depth 3.3 m), with contributions to transpiration ranging between 21 % and 90 % during drought, when surface soil water availability was limited. Our results suggest that deep soil is an essential water source for tropical trees that delays potentially detrimental drops in plant water potentials and stem water content when surface soil water is limited and could hence mitigate the impacts of increasing drought occurrence and intensity as a consequence of climate change. Quantitatively, however, the amount of deep-water uptake was low due to the trees' reduction of sap flow during drought. Total water uptake largely followed surface soil water availability and trees switched back their uptake depth dynamically, from deep to shallow soils, following rainfall. Total transpiration fluxes were hence largely driven by precipitation input.

Dry season plant water sourcing in contrasting tropical ecosystems of Costa Rica

AbstractTracer‐aided studies to understand plant water uptake sources and dynamics in tropical ecosystems are limited. Here, we report the analysis of dry season source water uptake patterns of five unique ecosystems of Costa Rica across altitudinal (<150–3,400 m asl) and latitudinal (Caribbean and Pacific slopes) gradients: evergreen and seasonal rainforests, cloud forest, Páramo and dry forest. Soil and plant samples were collected during the dry season in 2021. Plant and soil water extractions were conducted using centrifugation. Stem water extracted volume and stem total water content were calculated via gravimetric analysis. Water source contributions were estimated using a Bayesian mixing model. Isotope ratios in soil and stems exhibited a strong meteoric origin. Enrichment trends were only detected in stems and cactus samples within the dry forest ecosystem. Soil profiles revealed nearly uniform isotopic profiles; however, a depletion trend was observed in the Páramo ecosystem below 25 cm. More enriched compositions were reported in cactus samples for extracted water volumes above ~20% (adj. r2 = 0.34, p < 0.01). The most prominent dry season water source in the evergreen rainforest (74.0%), seasonal rainforest (86.4%) and cloud forest (66.0%) corresponded to well‐mixed soil water. In the Páramo ecosystem, recent rainfall produced by trade wind incursions resulted in the most significant water source (61.9%), whereas in the dry forest, mean annual precipitation (38.6%) and baseflow (33.1%) were the dominant sources. The latter highlights the prevalence of distinct water uptake sources between recent cold front rainfall (near‐surface soil storage) to more well‐mixed soil moisture during the dry season, revealing ecohydrological processing previously unknown in this tropical region.

Contrasting stem water uptake and storage dynamics of water-saver and water-spender species during drought and recovery.

Drought is projected to occur more frequently and intensely in the coming decades, and the extent to which it will affect forest functioning will depend on species-specific responses to water stress. Aiming to understand the hydraulic traits and water dynamics behind water-saver and water-spender strategies in response to drought and recovery, we conducted a pot experiment with two species with contrasting physiological strategies, Scots pine (Pinus sylvestris L.) and Portuguese oak (Quercus faginea L.). We applied two cycles of soil drying and recovery and irrigated with isotopically different water to track fast changes in soil and stem water pools, while continuously measuring physiological status and xylem water content from twigs. Our results provide evidence for a tight link between the leaf-level response and the water uptake and storage patterns in the stem. The water-saver strategy of pines prevented stem dehydration by rapidly closing stomata which limited their water uptake during the early stages of drought and recovery. Conversely, oaks showed a less conservative strategy, maintaining transpiration and physiological activity under dry soil conditions, and consequently becoming more dehydrated at the stem level. We interpreted this dehydration as the release of water from elastic storage tissues as no major loss of hydraulic conductance occurred for this species. After soil rewetting, pines recovered pre-drought leaf water potential rapidly, but it took longer to replace the water from conductive tissues (slower labeling speed). In contrast, water-spender oaks were able to quickly replace xylem water during recovery (fast labeling speed), but it took longer to refill stem storage tissues, and hence to recover pre-drought leaf water potential. These different patterns in sap flow rates, speed and duration of the labeling reflected a combination of water-use and storage traits, linked to the leaf-level strategies in response to drought and recovery.

Adsorption dynamics and hydrothermal stability of MOFs aluminium fumarate, MIL-160 (Al), and CAU-10-H, and zeotype TiAPSO for heat transformation applications

Metal-organic frameworks (MOFs) can be beneficial for heat transformation applications due to their potentially high water uptake and tunable working temperature levels. Although the hydrothermal stability has been assessed in some cases in terms of maximum water uptake and structural changes, there is no data on the impact of hydrothermal stress tests on adsorption dynamics. However, to maintain the designed heating or cooling power in the application, the hydrothermal stability in terms of both water uptake and adsorption dynamics is decisive. To close this gap, we present experimental data for the comprehensive evaluation of hydrothermal stability for three different MOFs and the commercially available zeotype TiAPSO. The hydrothermal stress test includes around 70,000 temperature swing cycles on aluminium sheets with a binder-based coating of different adsorbents. As a novelty of this study, adsorption dynamics are determined before and after the hydrothermal stress test using effective thermal resistances and the characteristic temperature difference. Our results show degradation in terms of a decrease in uptake around 5–10% after hydrothermal stress test for all samples. Under temperature boundary conditions relevant for the application, MIL-160(Al) shows even a drastic uptake reduction of around 35–45%. Except for CAU-10-H, none of the adsorbents show a degradation in terms of increased heat and mass transfer resistance. In case of CAU-10-H, the overall effective heat and mass transfer resistance increases by around 30–40% after the hydrothermal stress test. These results indicate that the hydrothermal stability of MOFs must be assessed in terms of both, uptake and adsorption dynamics, to ensure stable long-term performance in real-world devices.

Plant water uptake modelling: added value of cross-disciplinary approaches.

In recent years, research interest in plant water uptake strategies has rapidly increased in many disciplines, such as hydrology, plant ecology and ecophysiology. Quantitative modelling approaches to estimate plant water uptake and spatiotemporal dynamics have significantly advanced through different disciplines across scales. Despite this progress, major limitations, for example, predicting plant water uptake under drought or drought impact at large scales, remain. These are less attributed to limitations in process understanding, but rather to a lack of implementation of cross-disciplinary insights into plant water uptake model structure. The main goal of this review is to highlight how the four dominant model approaches, that is, Feddes approach, hydrodynamic approach, optimality and statistical approaches, can be and have been used to create interdisciplinary hybrid models enabling a holistic system understanding that, among other things, embeds plant water uptake plasticity into a broader conceptual view of soil-plant feedbacks of water, nutrient and carbon cycling, or reflects observed drought responses of plant-soil feedbacks and their dynamics under, that is, drought. Specifically, we provide examples of how integration of Bayesian and hydrodynamic approaches might overcome challenges in interpreting plant water uptake related to different travel and residence times of different plant water sources or trade-offs between root system optimization to forage for water and nutrients during different seasons and phenological stages.

Exploring the use of synthetic aperture radar data for irrigation management in super high-density olive orchards

Understanding the plant water-uptake dynamics and behavior in olive orchards is an area of much interest, particularly for efforts to optimize the use and application of water resources. However, plant water-uptake information is rarely available or consistently monitored for large agricultural areas, especially in developing countries. Here we evaluate the potential of using synthetic aperture radar (SAR) images to monitor the water-uptake rate in super high-density olive orchards located in the hot and arid desert climate of Saudi Arabia. The experiment was performed using Sentinel-1 data acquired between 2019 and 2020 in concert with in situ sap flow measurements. To date, no study has explored the potential of Sentinel-1 SAR data to assess the water-uptake rate in olive orchards. The results demonstrate that the SAR backscatter increased between January and July/August, and then decreased during the remainder of the year, following a broadly Gaussian distribution. Of key interest is the strength of the relationship between the increasing and decreasing trends of SAR backscatter and the variation in the coincident water-uptake rate measured in situ, producing a coefficient of determination of 0.81 in the VV polarization. As the relationship between the SAR backscatter and water-uptake rate was established for plots with similar tree type and planting density, further exploration of orchards with different characteristics and planting densities is needed to fully understand the potential of SAR data to estimate plant water-uptake. Overall, the study demonstrates that SAR data can track variation in locally measured water-uptake and illustrates the potential to assist with enhancing irrigation management.

The Characteristics of Time-Dependent Changes of Coefficient of Permeability for Superabsorbent Polymer-Soil Mixtures.

Water uptake dynamics of superabsorbent polymers (SAP) in soil is of key importance for the optimum application of these materials in environmental engineering and agriculture, so goal of this paper is to determine time dependent values of coefficient of permeability for various SAP-soil mixtures. Retaining water in soil is a key requirement in critical zones to support plant growth. There is an urgent need for technologies that can increase soil water retention, given the increasing prevalence of droughts and scarcity of clean water as the climate changes, combined with the rising demand for food by a growing world population. SAPs are materials that can absorb significant amounts of water, and thus have tremendous potential to help increase water retention in soil. However, while some studies have characterized the equilibrium swelling behavior of SAPs in soil, how their addition influences the time-dependent flow of water through soil remains poorly understood. Here, we address this gap in knowledge by directly measuring the coefficient of permeability of SAP-soil mixtures, testing different soil grain sizes, SAP grain sizes, and different SAP-soil ratios. We find that SAP addition can dramatically hinder the flow rate of water through soil—reducing the permeability by several orders of magnitude, and in some cases causing complete blockage of water infiltration, at mass fractions as small as 1%. In this scenario coefficient of permeability of 1.23 × 10−4 m/s dropped by a factor of ~10 after 14 min, a factor of ~100 after 36 min, and by nearly a factor of ~1000 after 63 min, eventually causing complete blockage of infiltration after 67 min. Authors concluded that in this particular situation the size and quantity of SAP particles was enough to nearly completely fill the available pore space resulting in rendering the soil column almost completely impermeable. Moreover, we demonstrate that these effects are well-described by a simple hydraulic model of the mutual interactions between SAP and soil grains, providing more generally-applicable and quantitative principles to model SAP-soil permeability in applications. Ultimately, this work could help evaluate the optimal proportions and grain sizes of SAPs to use for a given soil to simultaneously achieve a desirable permeability along with increased water holding capacity in the plant root zone.

Effect of acid treatment on the physico-chemical properties of Nafion 117 membrane

In this work, the effect on the physico-chemical properties of Nafion 117 membrane due to the treatment with HCl, H2SO4 and HNO3 was studied. Water uptake, crystallinity, proton conductivity and water dynamics were evaluated on treated and non-treated membranes. An increase in the water uptake and conductivity and a decrease in the crystallinity were observed in treated membranes in comparison with the untreated one. The water dynamics, studied by spin-spin NMR relaxometry, suggests that treated membranes have a more uniform channel size distribution. The treatment with HCl and HNO3 showed higher conductivity and water uptake than H2SO4.

Water uptake dynamics in apple trees assessed by an isotope labeling approach

Improving our knowledge on the relative contribution of irrigation water, precipitation, and groundwater to tree transpiration is necessary for an efficient and sustainable use of water resources in agriculture. For this purpose, we applied deuterium (2H) enriched water to trace the uptake of irrigation water by apple trees under field and pot conditions. 2H-enriched water was supplied to apple trees in an Alpine valley mimicking sprinkler irrigation. Labeled water infiltration in the soil and presence in apple tree shoots was measured over a week. An ancillary experiment using potted trees was performed to elucidate the role of irrigation water after soil saturation with 2H-enriched water. Under field conditions, 2H-enriched water infiltrated to a maximum depth of 0.6 m, where most of the fine roots were present, and mixed with pre-irrigation soil water. Sprinkler irrigation water was taken up by apple trees 2–4 h after its supply and its contribution to the shoot water content increased in the first 24 h, then it leveled off. Tree water absorbed from the enriched soil layer represented on average 48 ± 3% and 26 ± 2% of the total water in shoot axes and leaves, respectively. The results of the pot experiment confirmed the contribution of irrigation water to shoot water and allowed us to speculate that under field conditions groundwater (ca. 0.9 m deep, with capillary rise expected up to 0.6 m depth) did not significantly contribute to tree water uptake. Results indicate that a large fraction of shoot water (52–74%) did not derive from recent soil water uptake, suggesting a rather limited water mixing within tree organs.

Learning main drivers of crop progress and failure in Europe with interpretable machine learning

A wide variety of methods exist nowadays to address the important problem of estimating crop yields from available remote sensing and climate data. Among the different approaches, machine learning (ML) techniques are being increasingly adopted, since they allow exploiting all the information on crop progress and environmental conditions and their relations with crop yield, achieving reliable and accurate estimations. However, interpreting the relationships learned by the ML models, and hence getting insights about the problem, remains a complex and usually unexplored task. Without accountability, confidence and trust in the ML models can be compromised. Here, we develop interpretable ML approaches for crop yield estimation that allow us investigating the most informative agro-ecological drivers and influencial regions learned by the models. We conduct a set of experiments to learn the selection of agro-ecological drivers leading to best estimations of main crops grown in Europe: corn, barley and wheat. As input data, we consider a variety of multi-scale Earth observation products sensitive to canopy greenness (e.g. EVI and LAI), its water-uptake dynamics (e.g. VOD) and available water (soil moisture), as well as climatic variables from the ERA5-Land reanalysis (e.g. temperature and radiation). Our results show that the best performances (R2>0.55 for corn and R2>0.8 for both barley and wheat) are obtained when descriptors of soil, vegetation, and atmosphere status are used as input in the ML models. This combination of variables outperforms the results obtained using single variables as inputs or all variables altogether. We then further analyze the relations of input features with crop yield in the developed models by means of Gaussian Process Regression (GPR). We show how the information learned by the GPR model allows us to identify atypical or anomalous crop seasons across the study region, and investigate the underlying factors behind crop progress and failure in Europe.

Drought reduces water uptake in beech from the drying topsoil, but no compensatory uptake occurs from deeper soil layers.

Summary The intensity and frequency of droughts events are projected to increase in future with expected adverse effects for forests. Thus, information on the dynamics of tree water uptake from different soil layers during and after drought is crucial.We applied an in situ water isotopologue monitoring system to determine the oxygen isotope composition in soil and xylem water of European beech with a 2‐h resolution together with measurements of soil water content, transpiration and tree water deficit. Using a Bayesian isotope mixing model, we inferred the relative and absolute contribution of water from four different soil layers to tree water use.Beech took up more than 50% of its water from the uppermost 5 cm soil layer at the beginning of the 2018 drought, but then reduced absolute water uptake from the drying topsoil by 84%. The trees were not able to quantitatively compensate for restricted topsoil water availability by additional uptake from deeper soil layers, which is related to the fine root depth distribution. Absolute water uptake from the topsoil was restored to pre‐drought levels within 3 wk after rewetting.These uptake patterns help to explain both the drought sensitivity of beech and its high recovery potential after drought release.