Mixing and transport mechanisms of water in unsaturated shallow soil govern the partition of infiltrating water into the plant available water in soil water storage and groundwater recharge and modify the distribution of soil solutes and contaminants in subsurface. Consequently, they play a major role in the regulation of eco-hydrological processes at the soil–vegetation–atmosphere continuum. In sub-arctic regions, where both current and predicted warming rates are highest, the water cycle is undergoing marked changes and a limited understanding of storage and movement of water in soil has been recognized as one of the biggest knowledge gaps in addressing this issue. Stable isotopes of water are frequently used to explore water fluxes at the soil-vegetation interface, as they have proved to be a potent tool for tracing the origin and variability of waters that occupy different soil and plant compartments.
We used a combination of field experiments and surveys that utilize stable isotopes of water as both natural and artificial tracer to assess the main drivers of spatiotemporal variability of water fluxes at the soil-vegetation interface in a sub-arctic catchment. First, soil coring and xylem sampling campaign was performed to quantify the variability of soil water isotopes under different land covers and in different seasons, and further identify under which conditions is soil water isotopic composition reflected in the stem water. Afterwards, an irrigation experiment using deuterated water was carried out on a forested hilltop to understand how infiltrating water gets redistributed in subsurface and how sub-arctic forest till soil and vegetation respond to massive infiltration events. The studies were conducted at the Pallas catchment, located in Northern Finland.
We found that seasonal rainfall variation and late snowmelt events were clearly represented in forest till soils, while the water input signal was heavily attenuated in forested peatlands. However, the seasonal evolution of soil water pools was not reflected in tree stem dynamics. In addition, the main infiltration mechanisms in shallow till soil were delineated through an inspection of interplay between soil water fluxes of different mobility. We further observed how a large snowmelt event can cause an isotopic homogenization of all water fluxes at the soil–vegetation interface.
Our results highlight the unique role of snowmelt in replenishing and sustaining soil water storage and modifying isotope dynamics at the soil–vegetation interface.
How to cite: Muhic, F., Ala-Aho, P., Sprenger, M., Noor, K., Welker, J., Klöve, B., and Marttila, H.: Stable water isotope seasonality at the soil-vegetation interface in cold climate, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17243, https://doi.org/10.5194/egusphere-egu25-17243, 2025.
Mediterranean mountain regions are facing significant challenges due to climate change, including declining annual rainfall, prolonged dry spells, and increasingly frequent summer storms. These challenges pose serious threats to ecosystem resilience and the sustainable management of water resources and tackling them requires effective ecohydrological strategies. However, understanding water flow through the critical zone remains challenging due to the intricate water partitioning processes shaped by soil and vegetation heterogeneities. In an attempt to somewhat diminish this complexity, this study aims to investigate the water use dynamics of montane Scots pine (Pinus sylvestris L.) under varying wetness conditions by integrating ecohydrological data, stable water isotope (²H and ¹⁸O), and numerical modeling with Hydrus 1D.
We conducted a comprehensive plot-scale field investigation in the Vallcebre research catchments (NE Spain), monitoring two sets of three Scots pine trees since May 2022. Data collection included throughfall, sap flow, stem diameter variations, and soil water potential and content down to 70 cm depth, all at 5-minute intervals. Weekly sampling of different water pools (throughfall, bulk and mobile soil water down to 100 cm, groundwater, and xylem water) provided isotope data across the growing season of 2022. The analysis of these datasets revealed dynamic tree water uptake behavior, with shifts in source water contributions across variable wetness conditions. We observed that tree water uptake predominantly contained winter precipitation, even after a large summer storm delivering more than 60 mm of rainfall in a single day after a 20-day dry spell. However, later in the growing season, the isotopic composition shifted to reflect a roughly equal contribution from both summer and winter precipitation.
We used the Hydrus 1D model to test three distinct root distribution estimation methods and utilizing our field ecohydrological, and isotopic data as inputs. The simulations revealed that the choice of root distribution significantly influenced model performance. The model captured the patterns of soil moisture and atmospheric demand, particularly emphasizing how shifts in these factors influence tree water use efficiency and water stress responses. These findings demonstrate the importance of accurately representing root distribution in ecohydrological models to improve our understanding of tree water uptake processes. Our integrated approach provides a reliable framework for exploring the complex water dynamics in montane Scots pine ecosystems, offering insights into tree resilience under future climate scenarios.
Keywords: Ecohydrology; Soil-plant-water interactions; Stable isotopes; Modelling; Root distribution, Scots pine
How to cite: Alharfouch, L., Llorens, P., Hidalgo, J. J., Jiménez-Martínez, J., Castro-López, J. A., Gallart, F., and Latron, J.: Integrating ecohydrological, isotopic, and numerical approaches to assess water use in montane Scots pine under varying wetness conditions , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-412, https://doi.org/10.5194/egusphere-egu25-412, 2025.
Water stable isotopes are valuable proxies for tracing water fluxes within the critical zone, the Earth’s layer extending from vegetation through to deep aquifers. This technique has helped to develop conceptual models of water distribution across scales, making it essential to understand how trees regulate water stored within their internal compartments. To investigate this, we sampled a representative Pinus sylvestris tree within an ecohydrologically monitored forest plot in the Vallcebre research catchments (NE Spain). The primary aim of this sampling was to assess potential variability in the isotopic signatures across different parts of the tree to enhance understanding of soil-root-tree water uptake processes. Samples were collected from various soil depths (0–100 cm), woody tissues of twigs and branches (at 3 canopy heights), the stem (cores at 3 different heights), and roots in all four cardinal directions during two sampling days (July and September 2023). Water from soil and wood samples was extracted using: cryogenic vacuum distillation (CVD) and cavitron (centrifugation). Stable isotope ratios were measured for all samples using infrared laser spectrometry (Picarro). Additional data included long-term meteorological records, throughfall volumes and isotopic signatures, soil moisture content and potential, sap flow and tree water deficit rates (from adjacent trees). Results showed consistent patterns across sampling dates: twigs and branches displayed isotopic values close to those of soil and throughfall, whereas roots and stem tissues exhibited more depleted values, clearly distinct from soil, twig, and branch signatures. To determine whether these isotopic observed differences arise from methodological issues (differences between cavitron and cryogenic extractions and/or the part of the wood sampled) or reveal intrinsic processes within the tree, in a third sampling campaign (July 2024) we sampled soil, roots, stem, branches and twigs. From roots and branches we took samples for CVD and Cavitron extraction and from the stem we took heartwood and sapwood samples. In addition, selected samples from the third campaign will be analyzed by both Picarro and isotope ratio mass spectrometry (IRMS). This additional information promise new insights into the internal water dynamics of trees, clarifying if observed isotopic patterns reflect true physiological processes or methodological artifacts. This is critical for advancing our understanding of tree water dynamics and their role in critical zone water fluxes.
How to cite: Castro Lopez, J. A., Latron, J., Llorens, P., Alharfouch, L., Barbeta, A., Gimeno, T., and Martínez-Sancho, E.: Investigating stable isotope signatures variability across tree compartments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-944, https://doi.org/10.5194/egusphere-egu25-944, 2025.
Forested catchments play a key role in storing and releasing fresh water. Climate changes affect global hydrological and ecosystem processes with effects also observed at small scales. In this context, investigating spatial and temporal water origins in small forested catchments is fundamental to understand and better predict the behavior of hydrological processes. However, very little is known about both the spatial and temporal origin of water across different ecohydrological compartments in Mediterranean forested catchments.
In this study, we collected hydrometeorological and isotopic data in the Re della Pietra experimental catchment (2 km2) located in the Tuscan Appennines (Central Italy) to understand the origin of stream water at different spatial and temporal scales and the sources of tree-water uptake. Starting in April 2019, we collected water samples for isotope analysis (d18O, d2H) from precipitation, throughfall, springs, and the stream at different sections (4 locations from upstream to downstream). In addition, we sampled soil at different depths (0-20cm, 20-40cm, 40-60cm) and several monitored beech trees. Hydro-meteorological parameters are monitored in the Lecciona subcatchment (0.3 km2).
Results based on the HYSPLIT model revealed that the Northern Lower Atlantic dominates the water vapor of precipitation in both wet and dry periods. In contrast, water vapor from the Arctic Ocean was observed only in wet periods, while in dry ones, there was a small contribution of Mediterranean water vapor. Furthermore, there were significant spatial and temporal variations of isotopes (δ18O and δ2H) and electrical conductivity among water in various ecohydrological compartments. Both the main stream and the tributary were mainly recharged by spring water and only secondarily by precipitation and soil water with significant seasonal variations. Spring water decreased in wet periods but increased in dry periods, and precipitation and soil compartments showed opposite behaviours. Trees mainly used soil water from shallow layers(0-20 cm: 51.1% ± 13.1%, 20-40 cm: 37.1% ± 15.6%, 40-60 cm: 7.5% ±6.3%) in wet periods, while in dry periods, tree water uptake came from deep soil layers(0-20 cm: 13.41% ± 12.7%, 20-40 cm: 55.6% ± 26.1%, 40-60 cm: 8.35% ± 3.6%). The dominant negative values of the Seasonal Origin Index in all ecohydrological compartments except shallow soil layers revealed that winter precipitation was used even in midsummer by the trees and that both surface and subsurface water reflect larger contributions from winter sources. These results imply the resilient behaviour of this catchment to cope against summer droughts and provide a preliminary theoretical basis for managing forest and water resources in Mediterranean catchments.
How to cite: Feng, M., Manco di Villahermosa, F. S., Verdone, M., Murgia, I., Fabiani, G., Zuecco, G., Brighenti, S., Klaus, J., Massari, C., Borga, M., Jiang, M., and Penna, D.: Geographical, spatial, and temporal water sources in a Mediterranean forested catchment., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9957, https://doi.org/10.5194/egusphere-egu25-9957, 2025.
Ecohydrological studies aiming to understand patterns in root water uptake by trees based on plant and soil water isotope data are often confined to one or a few nearby locations. In this study, we took advantage of recently established pan-European hydrogen (δ2H) and oxygen (δ18O) isotope datasets (10.16904/envidat.542) to assess root water uptake depth for beech and spruce trees across Europe. For a subset of sites, δ17O data were available as well.
Our analysis revealed consistent isotopic enrichment in xylem water of spruce trees compared to beech trees across all mixed-species sites (N=13), suggesting that spruce predominantly used shallower soil water regardless of environmental conditions. Additionally, we observed isotopic enrichment in stem xylem water from spring to summer at most beech and spruce sites (N=32), suggesting both species relied on isotopically enriched summer precipitation. Interestingly, for a subset of sites (N=8), there was an inverse pattern, with isotopic depletion in summer, implying shifts to deeper soil water sources or uptake of shallow soil water that was isotopically depleted in summer compared to spring conditions.
To further explore these findings, we will visually and statistically examine them using isotope data from the soil (10–90 cm depth). We will analyze the role of climate (using gridded data), alongside site-, soil-, and tree-specific metadata to better understand the factors influencing the variation in root water uptake at the continental scale. Additionally, we will explore the potential of oxygen-17 excess to provide further insights into root water uptake dynamics.
How to cite: Lehmann, M., Geris, J., Penna, D., Rothfuss, Y., van Meerveld, I., and Meusburger, K.: Exploring root water uptake of beech and spruce trees across Europe , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18736, https://doi.org/10.5194/egusphere-egu25-18736, 2025.
Xylem is the plant tissue devoted to water transport. Its structure and anatomy vary among tree species, ranging from integrated (i.e., well-connected) to sectored networks. While xylem hydraulic sectoring has some advantages (e.g., reduced spread of pathogens and embolism), it also limits the exchange of water and nutrients between plant organs in different locations in the tree. In agricultural settings, where water and fertilizer inputs are often localized, preferential flow pathways in xylem could lead to non-homogeneous distribution of these resources within the trees. We therefore carried out an experiment to determine the degree of sectoriality in apple tree xylem, hypothesizing that differences in water availability at root level would influence this behavior.
To test our hypothesis, we potted young apple trees in a split-root system with four independent compartments. Soil compartments in different sets of trees were irrigated with water having different isotopic composition (enriched, δ2H ≈ 1650‰, or tap, δ2H ≈ -80‰) or left dry, obtaining five different treatments (100, 50_W, 25_W, 50_D, and 25_D, where the number represents the percentage of sectors receiving labelled water, and W and D indicate whether the remaining sectors were irrigated with tap water or left dry, respectively). Four days after the labelled irrigation, we destructively sampled shoots, trunk, rootstock, roots, and soil in each pot, every time collecting four samples corresponding to the respective sectors of the split-root system. Water was subsequently extracted from the samples by cryogenic vacuum distillation and its isotopic composition determined with IRMS. A two-end-member mixing model was applied to determine the contribution of labelled soil water in each tree organ.
In the trees receiving water in all sectors (100, 50_W, and 25_W), the average fraction of labelled soil water measured in the tree was consistent with that in the soil and reflected the number of soil sectors receiving labelled water in the respective treatment (100%, 50%, or 25% of enriched soil water). Conversely, when the labeled water was applied only to one or two soil compartments (25_D and 50_D), the average fraction of enriched soil water in the trees was higher than when the other compartments received unlabeled water (25_W and 50_W), indicating a higher water uptake by the roots in the irrigated sectors. Interestingly, in all treatments except the 100, we observed a high variability in the fraction of labelled soil water among different parts of the canopy within each tree. When soil water availability was homogeneous (50_W, 25_W), at least one sector of the tree canopy showed a negligible (<10%) contribution of labelled soil water, indicating that water flow was predominantly axial. When part of the soil was dry (50_D, 25_D), lateral water movement was enhanced, evidencing that hydraulic sectoring is affected by the water availability at root level. Therefore, when trees have access to water pools with different availability and isotopic fingerprint, the isotopic composition of water could be spatially variable also within the plant. This has consequences in ecohydrological studies.
How to cite: Giuliani, N., Haug, A.-L., Brighenti, S., Aguzzoni, A., Zanotelli, D., Penna, D., and Tagliavini, M.: Evidence of xylem hydraulic sectoring in apple trees from a deuterium tracing experiment in a split-root system, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3707, https://doi.org/10.5194/egusphere-egu25-3707, 2025.
In an agricultural field, crops in the Rabi and Zaid seasons are exposed to repeated wet-dry cycles between precipitation and/or irrigation events. There is a general consensus in the literature that no isotopic fractionation occurs during water uptake by the plants. The isotopic shifts in soil water at different soil tensions, if occurs during repeated wet-dry cycles, are expected to influence the isotopic composition of the plant’s xylem water. The objective of this study was to investigate the isotope enrichment and/or depletion during repeated wet-dry cycles in an agricultural field within the plant-available water range, specifically from field capacity to wilting point. The pressure-saturation curves and isotope retention patterns were compared to observe the changes in the isotopic compositions of plant-available water.
The laboratory experiments were conducted with soil (silty sand) from an agricultural plot that undergoes regular cultivation of 2-crops a year (Rice-Wheat) with no tillage. A modified pressure plate apparatus was fabricated to simultaneously measure the pressure vs. saturation and isotope compositions at each pressure. The pressure plate apparatus was designed to ensure mass balance across the imbibed, exuded, and retained water at each suction pressure, throughout all the wet-dry cycles. The experiments were conducted over five wet-dry cycles with the same reference water of known isotopic composition. The exuded water was analyzed directly, and the retained water content at each suction pressure of five wet-dry cycles was extracted using cryogenic vacuum distillation. The isotopic composition of all the samples was analyzed using an LGR OA-ICOS liquid water isotope analyzer.
The pressure-saturation curves across all five cycles exhibited no significant changes for drainage. Drained water, even at a small suction pressure of 0.1 bar, was enriched in both δ²H and δ¹⁸O compared to the isotopic composition of the imbibed water. Within a cycle, both δ²H and δ¹⁸O in the exuded water showed depletion as the suction pressure increased. The δ²H composition of the exuded water became enriched with the progression of the wet-dry cycles. The δ¹⁸O composition of the exuded water, on the other hand, showed depletion with the progression of the wet-dry cycles. These results indicate that plant xylem water may show a mismatch with irrigation water due to fractionation during the wet-dry cycles.
How to cite: c u, A., Ojha, R., and Guha, S.: Stable Isotope Fractionation in an Agricultural Field during Wet-Dry Cycles, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9711, https://doi.org/10.5194/egusphere-egu25-9711, 2025.
The partitioning of precipitation into streamflow (Q) and evapotranspiration (ET ) is a fundamental aspect of the terrestrial
water cycle. Gaining insights into the mechanisms governing precipitation partitioning is critical for nutrient transport in
surface and subsurface water fluxes, ensuring plant water supply and maintaining atmospheric water dynamics. While previous
studies have highlighted the role of seasonal variability in precipitation partitioning, the influence of event characteristics
on precipitation partitioning has received less attention. In this study, we used hydrometeorological and tracer data from a
forested headwater catchment (Wüstebach, DE, 38.5 ha ) and a tracer-aided model based on StorAge Selection (SAS) functions
to quantify precipitation partitioning across different event types (mild, moderate and intense) and seasons after a period
of one year. Similar to previous studies, we showed seasonal precipitation input variability affects its partitioning.
Roughly about 82 % of spring season precipitation is released back into the atmosphere after one year, while this rate decreased
to 41 % for autumn season precipitation. Different season’s precipitation showed variation in partitioning to streamflow as
well. Approximately 11 % of autumn season precipitation ended in streamflow after one year, while this rate decreased to
3 % for spring season precipitation. However, within the same season, event characteristics showed stronger variation in
the partitioning of precipitation to ET and Q. Independent of in which season the precipitation fell, from mild to intense
events, ET partitioning decreased, and Q partitioning increased. Particularly for autumn precipitation, event types showed the
greatest variation in partitioning to ET and Q. ET partitioning for autumn precipitation declined roughly by 30%, Q partitioning
increased by 2%, and the fraction of precipitation remaining in the storage increased by 30% from mild to intense events. For
winter, ET decreased by 20 %, and Q and storage both increased by 6% and 15%, respectively. These patterns were consistent
across all seasons, indicating that precipitation event characteristics exerted a strong influence on the long-term partitioning
of precipitation. Thus, while seasonal variability remains important for precipitation partitioning, our results highlight which
type of precipitation returns to the atmosphere, contributes to discharge, or persists within catchment storage. These findings
emphasize the need to consider event-level precipitation dynamics under changing climatic conditions, given their potential
to alter water availability, contaminant transport, and flood mitigation strategies.
How to cite: Türk, H., Benettin, P., Stockinger, M., and Stumpp, C.: Precipitation event characteristics influence its partitioning into evapotranspiration and streamflow regardless of the season, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1690, https://doi.org/10.5194/egusphere-egu25-1690, 2025.
Belowground niche partitioning is a key mechanism for maintaining plant species diversity in grasslands. However, limited empirical data and precise methodologies restrict our understanding of plant belowground coexistence strategies. Here, we examined various scenarios of plant species niche overlap based on their water uptake depths. The study was conducted across 75 grassland plots within the Biodiversity Exploratories in three distinct German regions, using the natural abundance of oxygen stable isotopes (δ18O) to link the plant xylem water to its source depth in the soil (up to 50 cm). By applying plot-level and regional-level mixed model statistical methods, we first tested the accuracy of water uptake depth predictions of 25 species as one of the critical steps. These water uptake depth predictions were then used to calculate the overlap in resource uptake niches among single-species water uptake flexibility across regions, as well as different growth forms and root systems of species.
Our results demonstrate that water uptake depths strongly correlate with environmental factors such as soil type and the geographical gradient of the plots. Regional-level mixed models demonstrated higher accuracy, revealing similar variations in water uptake depths across regions and species compared to the plot-level approach, highlighting diverse water use strategies in grasslands. Furthermore, our niche overlap findings indicate that fibrous root systems generally show greater overlap than taproot systems. Additionally, the overlap calculations for single species across three regions showed diverse patterns, emphasizing the utility of stable isotopes in addressing various ecological questions. These findings enhance our understanding of belowground coexistence mechanisms and ecosystem dynamics, emphasizing the importance of precise measurement techniques in revealing the complex interactions that drive resource use in temperate grasslands.
How to cite: Golshani, S., Hájek, T., Schöllkopf, U., Harisson, J., Jafari, H., Rybová, B., Tielbörger, K., and Májeková, M.: Belowground niche partitioning and water uptake dynamics in temperate grasslands using stable isotopes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16403, https://doi.org/10.5194/egusphere-egu25-16403, 2025.
The reliability of soil water stable isotope analysis is -among other things- based on a correct soil water extraction. Currently used extraction methods are prone to isotope fractionation (especially with clay samples) and exhibit shortcomings limiting and/or complicating their usage. A newly developed soil water extraction method –Circulating Air Soil Water Extraction– is based on the principle of complete evaporation and condensation of the soil water in a closed circuit. Owing to its simple design, there is no need for any chemicals, gases, high pressure or high-temperature regimes. On the other hand, at present, the proposed apparatus with four independent extraction slots can be used at most twice a day.
The experimental tests proved no significant isotope fractionation effects leading to erroneous results caused by the extraction. In all experiments, the δ18O and δ2H did not exceed the limits ± 0.2 ‰ and ± 2 ‰, respectively, which is fully acceptable for hydrologic studies. Extraction of pure water samples shifts the isotope composition by 0.04±0.06 ‰ and 0.06±0.35 ‰ for δ18O and δ2H, respectively.
Soil water extraction tests were conducted with five distinct soil types (loamy sand, sandy loam, sandy clay, silt loam, and clay) using 40-150 grams of pre-oven-dried soil, which was subsequently rehydrated to 10 and 20 % water content. The shift in the isotopic composition ranged from -0.04 and 0.07 ‰ for δ18O and from 0.4 to 1.3 ‰ for δ2H with the corresponding standard deviations ± (0.08 – 0.25) ‰ and ± (0.34 – 0.58) ‰. The results exhibit high accuracy which predetermines this method for high-precision studies where unambiguous specification of the water origin is required. The accuracy is adversely counterbalanced by a reduced number of processed samples per day: at present eight (2 x 4 simultaneously measured samples at four extraction slots).
The proposed extraction method has proven versatility in handling various soil types with different soil textures and water contents. The main advantages are the high accuracy of the results, simple design of the apparatus setup, low operating costs, time reduction in operating the device, easy maintenance, and the ability to process large soil samples providing large and representative quantities of soil water.
How to cite: Kocum, J., Haidl, J., Gebouský, O., Falátková, K., Šípek, V., Šanda, M., Orlowski, N., and Vlček, L.: A new laboratory approach to extract soil water for stable isotope analysis from large soil samples, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12138, https://doi.org/10.5194/egusphere-egu25-12138, 2025.
The climate-change-induced increased frequency of droughts and shifts in rainfall patterns will most likely impact the interaction of trees with components of the hydrological cycle, e.g., rainfall, soil water, or groundwater. To study this, an increasing number of scientists use in-situ measurement systems capable of high-resolution measurement of the stable water isotopes (δ18O, δ2H) of xylem and soil water. These systems often use gas-permeable probes to sample water vapor in isotopic equilibrium with the liquid xylem or soil water, which are connected to transport tubing of several meters length that guide the vapor sample to the gas-inlet of a field-deployed isotope analyzer. Potential issues of these systems include (a) the accidental transport of liquid water to the isotope analyzer (e.g., by damage to the tubing, or inadequate sealing of connections), and (b) the maximum transport tubing length to obtain a reliable measurement. Here, we tested two different syringe filters (0.45 µm Nylon, and 0.2 µm PTFE) in terms of preventing liquid water from passing through, and from allowing water vapor to pass through without fractionation of isotope ratios. By switching between two known water sources, we further analyzed the effect of a possible filter cake made up of water vapor of the previous measurement trapped in the filter material on subsequent isotope measurements (memory effect). Lastly, using a 4 mm diameter tube we tested lengths from 1.3 m to 15.3 m in 1-m-increments to assess maximum tubing lengths for a reliable analysis. Results showed that only 0.2 µm filters were able to prevent liquid water from breaking through, and that isotope values were slightly enriched (δ18O: +0.47‰, δ2H: +1.3‰). However, this enrichment was not statistically significant due to the small sample size of only three repeated measurements with and without the filter installed. No influence of a possible filter cake was found as two waters of known isotope ratios could be repeatedly measured when switching back-and-forth between water sources (standard deviations were on average 0.15‰ for δ18O and 0.6‰ for δ2H). Tests of tubing length showed a maximum length of 6.3 m for the isotope ratios to reach the target value when measuring for 20 minutes. Between 15.3 m to 12.3 m, no discernible change in isotope ratios was detected, and from 12.3 m to 7.3 m the expected isotope ratio was only detected after the 20-minute measurement window. Using the vapor volume of our 4 mm diameter and 6.3 m long tube of approximately 80 cm³, we calculated that the often-used tubes of 1/8-inch inner diameter (~1.58 mm) could theoretically be up to 40 m long. We thus recommend using a maximum transport tubing length that corresponds to approximately 80 cm³ of gas that needs to be transported. If liquid water intrusion might pose a danger to field-deployed measurement equipment, 0.2 µm PTFE syringe filters can be used to stop the liquid water. However, the issue of potential fractionation of these filters is not yet resolved.
How to cite: Stockinger, M. and Stumpp, C.: In-situ measurement of the stable isotopes of soil and xylem water using liquid-vapor equilibration: protection against water intrusion and maximum tubing lengths for automatic systems, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3627, https://doi.org/10.5194/egusphere-egu25-3627, 2025.
This study investigates the dynamic behavior of snow in semi-arid mountainous landscapes, emphasizing the use of the isotope signal as a tool for tracing hydrological processes. Thin snowpack poses a significant challenge, leading to extensive shifts in isotope values and complicating the estimation of catchment-average snowpack signatures. Traditional mixing models fall short in such scenarios, necessitating detailed approaches involving sampling along the hydrological pathway. The research employs a tracer-enabled spatially-distributed, process-based ecohydrological modeling approach to evaluate groundwater recharge processes in the complex settings of a regional watershed in the Middle Atlas mountains of Morocco. The study's objectives are to quantify recharge rates and dynamics seasonal variations, conducting a comparative analysis of yearly to sub-seasonal trends dating from 2017 onwards, and exploring stable isotope dynamics in snow-fed compartments of the hydrological cycle. The preliminary results of the ecohydrological simulations are discussed ; the simulated streamflow exceeds observed values, attributed to factors such as low winter evapotranspiration and the generalized spatialization of parameters. Variations in water table levels of each aquifer, and evapotranspiration data reveal a time lag influenced by seasonal variations and vegetation density. Stable isotopes closely mirror observed data, indicating the model's capability to capture the dynamic behavior of the aquifer system, with spatialized maps revealing a time delay between peak SWE (Snow Water Equivalent) abundance and isotopic depletion. Recharge dynamics are notably influenced by Triassic clay formations, with higher rates in exceptionally wet years and variations based on geological properties. The study highlights the important role of SWE in groundwater recharge, with peak SWE coinciding with major recharge events, and decreasing SWE contributing to groundwater depletion.
Keywords: Recharge, snowpack, isotope, ech2o-iso, snowmelt.
How to cite: Rhoujjati, N., Kuppel, S., Ait Brahim, Y., Rhoujjati, A., Patris, N., Bouchaou, L., Attou, T., and Hanich, L.: Isotope-Enhanced Ecohydrological Modeling of Snow-Driven Recharge in Semi-Arid Mountains, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7378, https://doi.org/10.5194/egusphere-egu25-7378, 2025.
Intrinsic water use efficiency (iWUE) is a critical characteristic for optimizing cassava (Manihot esculenta Crantz) performance under climate change. Stable isotope composition provides a valuable tool for estimating iWUE, yet the key drivers of isotope variation across the cassava canopy remain unclear. In this study, conducted at 17 farms across three agroecological zones in the Eastern Democratic Republic of Congo, we examined how agronomic practices (fertilizer application and weeding) influence carbon (δ¹³C) and oxygen (Δ¹⁸O) isotope composition at different canopy positions and in carbohydrate pools during the bulk root initiation stage. Physiological and morphological variables were measured at noon across the upper, middle, and lower canopy of cassava plants grown on-farm during the rainy season. These variables were related to δ¹³C and Δ¹⁸O in bulk leaf material, extracted cellulose, and soluble sugars.
Fertilizer application increased δ¹³C of soluble sugars (+0.6 ‰, p < 0.1) and bulk (+0.3 ‰, p < 0.1) in the drier zone, suggesting enhanced iWUE under fertilized conditions. Path analysis showed that leaf nitrogen concentration became increasingly correlated with δ¹³C from the upper to the lower canopy, while the influence of stomatal conductance declined. In upper-canopy leaves, higher stomatal conductance was associated with elevated vapour pressure deficit (VPD), possibly due to co-varying increased light intensities. Assumptions of the dual isotope approach related to Δ¹⁸O were not met, and therefore require further investigation. These findings provide new insights into the drivers of iWUE in cassava, highlighting the roles of canopy position and agronomic practices. This knowledge can inform strategies to improve cassava resilience and productivity under climate change.
How to cite: Munyahali, W., Van Laere, J., Barhebwa, F., Birindwa, D., Merckx, R., Hood-Nowotny, R., and Dercon, G.: Effects of fertilizer and weeding on stable isotope composition (¹³C–¹⁸O) in different carbohydrate pools across the cassava canopy, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8051, https://doi.org/10.5194/egusphere-egu25-8051, 2025.
The effects of drought on coffee yield and quality during the flowering and fruiting stages are becoming a challenge in many coffee-producing regions. Nevertheless, coffee plants exhibit various adaptive mechanisms that mitigate the effects of short-term water scarcity during these phenological phases. Plants undergo numerous physiological and metabolic alterations in response to water deficits during their critical developmental stages, for example, during flowering, one of the stages that is related to yield. Although understanding these responses is essential for effective breeding and management strategies, they remain inadequately documented for coffee. This study employed a rapid and accurate method of pulse labelling utilising 13C-CO2 on 32 four-year-old Venecia Arabica coffee plants from Costa Rica in a greenhouse. Carbon assimilation in young and old leaf pairs was assessed at 10, 11, 12, and 13 days post-stress initiation to determine the metabolic differences in leaf age and orientation. The allocation of assimilates to soluble sugars, starch, and cellulose in various structural components, such as fruits, stems, roots, and old and young leaves, was also measured at harvest (15 days of stress). These findings demonstrate a significant reduction (p< 0.05) in carbon assimilation and, consequently, photosynthesis under drought stress conditions, with a more pronounced decrease in older leaf pairs. This study revealed altered assimilate partitioning, with plants prioritising allocation to roots to presumably sustained soil water uptake. Conversely, under water stress, carbon allocation to young leaves diminished, whereas in fruit, a priority sink, the assimilates remained constant for starch but increased for sugar (0.33±0.21%). Carbohydrate metabolism exhibited notable changes, including a significant (p< 0.05) decrease in foliar soluble sugars and enhanced starch allocation to stems and roots. Additionally, a significant (p< 0.0001) increase in cellulose production was observed, particularly in the older leaves (94%), stems (93%), and roots (89%), which suggests a physiological drought response with the upregulation of cellulose production, possibly providing structural support and protection against herbivory. In summary, this study revealed a response to short-term water deficit between the two leaf age categories and clarified the allocation of new assimilates in Coffea arabica. L. This study provides a foundation for improved breeding and management strategies to support the resilience and sustainability of coffee production.
How to cite: Nakamya, J., Van Laere, J., Hood-Nowotny, R., Merckx, R., Resch, C., Mitchell, J., Trust, B., and Dercon, G.: Effects of drought stress on assimilation and carbon allocation in a fruiting arabica coffee plant explained by 13C-CO2 pulse labelling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8143, https://doi.org/10.5194/egusphere-egu25-8143, 2025.
Climate change is causing more frequent heat waves and droughts in recent summer in the Mediterranean area. This phenomenon is posing risks for viticulture, regarding both the quantity produced and the quality of the wines. Adaptation and mitigation measures to climate change effects include the use of emergency irrigation and soil management practices. In this context, ecohydrological studies about the water dynamics in the soil, as well as the patterns and variability of vines root water uptake (RWU) depth throughout the growing season, can provide valuable insights for achieving more efficient and sustainable water resource use in viticulture.
As part of the Interreg Ita-Slo IRRIGAVIT project, during the 2024 growing season, we conducted an ecohydrological characterization of a vineyard cultivated with Vitis vinifera cv. Ribolla Gialla (grafted on Kober 5BB) on a terrace in Corno di Rosazzo (Friuli Venezia-Giulia, Northeast Italy), using stable water isotope composition (δ18O, δ2H, d-excess) to track water fluxes in the soil-plant-atmosphere continuum. The site was chosen due to its soil composition, primarily consisting of flysch residuals (weathered alternations of marls and sandstones).
We sampled monthly precipitation from February 2024 to January 2025, as well as individual precipitation from spring to late summer 2024. In the plot located on the highest terrace of the hillslope, we sampled soil and vines sap every two to three weeks, collecting three soil cores and nine sap samples per sampling date. Soil cores were divided into 10 cm segments down to 35 cm of depth and 20 cm segments from that to the maximum reached depth (more than 1 m). Soil water was extracted in the lab using a cryogenic vacuum distillation (CVD) line. Sap samples were extracted using a vacuum pump system in the field from three shoots of plants close to each drilling point.
Rainwater and soil water samples were analysed using a CRDS laser spectroscope Picarro L2130-i in liquid mode, while the sap samples were analysed with the same instrument, coupled with a Picarro Induction Module to minimize the organic spectral interference. In addition, soil water content and water potential were measured, and soil mineralogy and particle size were assessed. Soil moisture and plant water potential were monitored in the field.
The 2024 growing season was particularly challenging for viticulture in Northeast Italy: frequent rainfall in spring damaged vines’ flowers, the summer was hot and dry, while heavy rainfall occurred during harvest. Visual inspections of soil samples revealed roots reaching up to 1.50 m deep. Isotopic data indicated that vines RWU occurred mainly in the top 20 cm of soil, which retained sufficient moisture even during the hot, dry summer with high vapour pressure deficit (VPD) values. This may have been due to soil management practices, such as using shredded cover crops to create mulch, enriching the topsoil with organic matter and improving water retention.
How to cite: Peschiutta, M., Posocco, V., Tomasella, M., Biruk, L. N., Sivilotti, P., Alberti, G., Masiol, M., Zini, L., Calligaris, C., Dreossi, G., Sodini, M., Lisjak, K., and Stenni, B.: Ecohydrological characterization of a terraced hill vineyard in Corno di Rosazzo (Italy), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8739, https://doi.org/10.5194/egusphere-egu25-8739, 2025.
The increase in average temperatures and change in precipitation patterns derived from climate change affect forests differently, varying from the species' composition and forest characteristics. Understanding the ecophysiological behavior of trees under climate change and its impacts on the hydrological processes on a catchment scale requires a multidisciplinary approach, with an initial focus on the interactions on the soil-plant-atmosphere continuum. To better characterize soil water availability dynamics and comprehend how it may be affected by climate change, water isotope ratios of conservative tracers (δ18O, δ2H) can be used as fingerprints of infiltration processes, providing information on the seasonal origin of soil water infiltrated in the vadose zone. This study aims to characterize profiles of water isotopes in soil water to evaluate its seasonal isotope distribution. This information will be essential for further evaluations of seasonal water use by trees, contributing to understanding processes from the plot to the catchment scale.
The study will be conducted in an experimental plot (DRAIN Station) in the Rosalia catchment (950 ha), located on the border between the Austrian states Burgenland and Lower Austria. The catchment elevation ranges from 385 to 725 m, with a mean annual precipitation of 790 mm and a mean annual temperature of 8.2 °C. The soils are predominantly Cambisols, and the main land use comprises forests, predominantly beech (Fagus sylvatica) and Norway spruce (Picea abies). The DRAIN Station is located upstream in a beech stand representative of the forest in the catchment and has an average slope of 16°. This plot is a permanent monitoring station part of the LTER (Long-Term Ecosystem Research), a global network focused on long-term measurements of nitrogen, carbon, and water balance. A variety of environmental variables are measured at plot and catchment scale, adding spatial and temporal heterogeneity in the evaluation of hydrological processes.
At the DRAIN Station, a transect of four soil profiles representative of the plot will be defined and soil samples will be collected every 5-10 cm down to 60 cm using a split spoon sampler. To determine the precipitation water isotope ratios, daily precipitation data collected at the catchment’s climate station will be analyzed. The soil and water samples will be analyzed in the laboratory for stable isotopes (δ18O, δ2H) using a Picarro laser-spectroscope. The mean monthly water isotope ratios in precipitation will be determined over 12 months and compared with the water isotope profiles of δ18O and δ2H.
These results will enhance the understanding of the infiltration processes and seasonal distribution of water fluxes in the vadose zone. Moreover, the spatial variability of isotope ratios among soil profiles, such as infiltration depth and velocity, will be assessed. By integrating the seasonal isotope distribution in soil profiles with transit time distribution and hydrological modeling, a deeper understanding of the hydrological processes across different scales can be achieved.
How to cite: de Bastos, F., Stockinger, M., Asanza-Grabenbauer, M., and Stumpp, C.: Seasonal isotope distribution in soil profiles and its implications for plant water uptake, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8777, https://doi.org/10.5194/egusphere-egu25-8777, 2025.
Seasonal floodplain forests are important ecosystems that attenuate floods and have high biodiversity. However, floodplains are threatened by human activities, such as dam building, agricultural water use, and climate change. Improving our understanding of the functioning of floodplain forests can aid in their protection. Trees in the floodplain forests in southeastern Brazil experience flooding for more than a month per year but also must endure very dry periods where the groundwater level is several meters below the surface. Species composition depends on the flooding regime, but which water the trees use for transpiration is largely unknown. As a result, their vulnerability to changes in climate or flooding regime remains poorly understood.
We sampled the different water sources (precipitation, streamflow, groundwater, and soil water at different depths) and vegetation (covering more than 60 tree species) across six floodplain forests in the Rio Grande and São Francisco basins in southeastern Brazil during four campaigns (two dry and two wet seasons). At each floodplain, we took samples from three different “eco-units”: levees (close to the river), terraces (wettest parts of the floodplain), and plains (regions that do not get flooded). The samples were analyzed for the abundance of hydrogen and oxygen stable isotopes. These data were used together with the MixSIAR model to investigate the contribution of soil water (down to 1 m) for tree water uptake.
The variability in xylem water was large and there was no consistent variation in the isotopic composition of the soil water between the dry and wet seasons. Instead, soil water reflected the isotopic signature of wet season precipitation and overbank flow. We hypothesize that the soil isotopic signature is reset by precipitation and overbank flow every wet season. There was also no consistent pattern in the isotopic composition of the xylem water across the three “eco-units”. The mixing model analyses suggest that for the floodplains in the Rio Grande basin, soil water was the main source during the wet season (64% ± 17) but not during the dry season (43% ± 17), when groundwater or stream water were the predominant sources. For the floodplains in the drier São Francisco basin, soil water was the main source of tree water uptake (60% ± 17 and 72% ± 15 for wet and dry seasons, respectively). However, uncertainties are very high due to the similar isotopic composition of the potential source waters.
How to cite: Meyer Oliveira, A., Floriancic, M., Moreira Gianasi, F., Herbstritt, B., Vieira Pompeu, P., de Carvalho Araújo, F., Maciel Silva-Sene, A., Gama Reis, M., Farrapo, C., Aparecido Silva Ferreira, L., Manoel dos Santos, R., and van Meerveld, I.: Which water sources do trees on floodplains in southeastern Brazil use for transpiration?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10527, https://doi.org/10.5194/egusphere-egu25-10527, 2025.
Agricultural crops play a crucial role in the global water cycle. Yet, climate change may alter crop physiology, agricultural ecosystems, and interactions within the land-atmosphere (L-A) system. Understanding crop transpiration (T) and soil evaporation (E) rates, along with their temporal dynamics and connection to the L-A system, is essential for predicting future hydro-climatic conditions and assessing agricultural land-use practices, particularly under the increasing frequency of extreme weather events.
Here, we introduce the DFG Research Unit “LAFI” (Land-Atmosphere Feedback Initiative) subproject 3, which focuses on partitioning evapotranspiration into E and T using real-time water isotope in-situ measurements.
We will study water fluxes and their isotopic composition across the L-A system to investigate water-related processes in high temporal and spatial resolution via canopy and leaf chambers for evapotranspiration (ET) and T, as well as membrane probes for soil water vapor isotope measurements. This innovative isotope measurement platform will enable the determination of root water uptake (RWU) contributions and depths for key crop species (wheat and maize) at the Land-Atmosphere Feedback Observatory (University of Hohenheim, Germany). Additionally, it will facilitate the evaluation of water transit times and the partitioning of ET.
Analyses will be species-specific and will examine the impact of varying environmental conditions on RWU, water transit times, ET, and ET partitioning. The results will provide insights into the vulnerability of crop species to climate-induced changes in precipitation patterns and soil moisture availability.
How to cite: Orlowski, N. and Kübert, A.: DFG Research Unit: Land-Atmosphere Feedback Initiative (LAFI): Using real-time isotopic in-situ measurements to partition evapotranspiration into soil evaporation and plant transpiration at two distinct cropland sites , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11886, https://doi.org/10.5194/egusphere-egu25-11886, 2025.
crouvenaz@student.ethz.ch
floriancic@ifu.baug.ethz.ch
The forest water cycle is dominated by vegetation-mediated processes, such as interception, infiltration, and transpiration, that greatly affect the redistribution of water between the atmosphere and subsurface. Yet, subsurface water transport and storage are poorly understood, complicating comprehensive analyses of tree water uptake.
Here we explore the performance and sensitivity of the model EcH2O-iso with a novel isotope tracer dataset from the WaldLab experimental forest site, a small catchment located in a mixed beech and spruce forest in Zürich, Switzerland. Five years ago, we began measuring water fluxes and stable water isotopes in precipitation, soils of various depths, groundwater, streams and xylem. The model EcH2O-iso is a process-based, spatially distributed ecohydrological model which allows to use water isotopic tracers (2H and 18O) for age tracking. Each grid cell is locally coupled with energy balance, hydrological transfer, vegetation growth and dynamics.
After setting up and parametrizing the model we validated model outputs with the measured isotope timeseries in different depths of the soil, groundwater, streamflow and xylem water along the sampled hillslope. We also tested to what extent input precipitation isotopes measured outside the forest are a reliable input to the model, by rerunning simulations with inputs from i) measured throughfall isotopes and ii) isotopic values obtained from drainage from the forest-floor litter layer. We performed multiple sensitivity analyses to better understand the sensitivity of certain model parameters and assessed which parameters need to be calibrated more precisely for future use of the model for this site.
How to cite: Rouvenaz, C. and Floriancic, M.: Revealing the origin and age of tree water uptake along a forested hillslope, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9792, https://doi.org/10.5194/egusphere-egu25-9792, 2025.
The EU-Horizon project CryoSCOPE, launched in February 2025, investigates the interplay between atmospheric, cryospheric, and hydrologic systems across varied landscapes, including the Swiss Alps, Finnish Lapland, Svalbard, and the Himalayas. A key focus in CryoSCOPE is to quantify hydrologic partitioning—how precipitation is distributed among streamflow, groundwater, and evapotranspiration—in snow-dominated environments. By integrating stable water isotope data in different hydrological fluxes, evapotranspiration measurements from mobile flux towers, and extensive hydrometeorological data, CryoSCOPE will quantify partitioning processes over seasonal and interannual scales. This presentation highlights a case study from Waldlabor, a forested site in Switzerland, demonstrating the observed seasonal hydrological partitioning patterns.
CryoSCOPE emphasizes expanding stable water isotope datasets in cold regions, enhancing insights into hydrologic dynamics in snow-dominated systems. These efforts aim to improve predictive models and support sustainable water resource management in globally relevant “cold spots”. By advancing understanding of water distribution and movement in cold environments, CryoSCOPE provides critical knowledge to inform water management and policy development in the face of climate change.
How to cite: Mungle, D., Floriancic, M., Molnar, P., and Beria, H.: CryoSCOPE: Quantifying hydrologic partitioning in snow-dominated landscapes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14397, https://doi.org/10.5194/egusphere-egu25-14397, 2025.
Partitioning of evapotranspiration (ET) is a fundamental challenge in ecohydrological research, critical for advancing our understanding of the soil-plant-atmosphere continuum. This study investigates ET partitioning for spring wheat crops grown at an experimental plot at IIT Kanpur using the stable isotopes of oxygen and hydrogen. By exploiting the distinct isotopic signatures of evaporation (E) and transpiration (T), the contributions of these processes to total ET were quantified. The isotopic compositions of ET and E were determined using the Keeling plot and the Craig-Gordon model respectively, whereas the isotopic composition of the stem was taken as the isotopic composition of T. Sensitivity analysis was performed to identify and prioritize the accurate measurement of variables significantly influencing ET partitioning. Results indicated that the transpiration fraction in ET varied between 38% and 96%, depending on crop growth stage and water availability. A comparison of results from isotopic methods and hydrometric methods revealed good agreement on most days, with discrepancies on some days attributed to uncertainties in estimating key parameters such as temperature and relative humidity. To capture interannual variability, additional experiments were conducted in subsequent years, providing further insights into the dynamics of ET partitioning.
How to cite: Singh, P., Balan, D., Ojha, R., Srivastava, R., Tripathi, S., Guha, S., Krishan, G., and Rao, M.: Evapotranspiration partitioning using stable isotopes of O and H, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14569, https://doi.org/10.5194/egusphere-egu25-14569, 2025.
Deep roots play a vital role in water and nutrient uptake and supply to assist in higher tolerance of increasing drought events under current global climate change scenarios. However, few studies have been made under field conditions to identify the differences between species and genotypes of grasses in root traits, water use efficiency (WUE), and nutrient uptake under drought stress. Stable isotope applications have revolutionized our understanding of water and nutrient dynamics in root systems, offering precise insights into plant resource uptake. In this study, experiments with grasses were done in a large-scale semi-field root phenotyping facility (RadiMax) equipped with rainout shelters to simulate drought conditions. In five experiments from 2016 to 2023, we measured the variations of root traits related to rooting depth among grass species and genotypes. The RadiMax facility enables the observation of root growth in up to 600 lines of diverse species and genotypes, with 150 to 300 lines being utilized in various grass experiments. Root traits were observed through minirhizotrons to more than 2 m depth and were quantified using an AI-based image analysis system (RootPainter). The RadiMax facility also allows deep placement of stable isotopes (2H and 15N), to be used as tracers for deep uptake by the root system. In this study, stable isotopic labelling was used in three studies from 2019 to 2023, in combination with the natural enrichment of 13C as a drought stress indicator. In this way, direct root phenotyping through minirhizotrons was combined with deep root function phenotyping based on the stable isotope measurements. Our preliminary results indicate that deep rooting will benefit plants as it contributes to deep water uptake under drought conditions, which indicates that selecting deep root traits should be included in the breeding of grass cultivars, to develop more drought-resilient genotypes.
How to cite: Li, Q., Svane, S. F., Popovic, O., Statiris, G., and Kristensen, K. T.: The role of deep roots in enhancing drought tolerance and nutrient uptake in diverse species and genotypes of grasses, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17104, https://doi.org/10.5194/egusphere-egu25-17104, 2025.
In ecohydrology, stable water isotopes (δ2H and δ18O) are valuable tools for investigating the water’s movement through the soil-plant-atmosphere continuum. Recent tracer-based studies using stable water isotopes showed that different methods for extracting water from plant tissues can return different isotopic compositions due to the presence of organic contaminants and because these methods extract different plant water domains. While Cryogenic Vacuum Distillation (CVD) is widely recognized as a standard method of plant water extraction for isotopic analysis, its indiscriminate water extraction has proven problematic. Various other techniques have been developed and tested for plant water extraction, such as direct vapour equilibration, mechanical squeezing and centrifugation. However, there remains a necessity to develop a cost and time efficient method to discriminately extract xylem water, which better represents the source waters used by plants for transpiration.
In this work, we evaluated the viability of Vacuum Extraction (VAC) - a method previously used in ecophysiology for chemical analysis - for the extraction of plant water for isotopic analysis. The specific objectives were to i) assess the likely influence of organic contaminants (glucose, fructose, sucrose, ethanol and methanol) in water samples extracted by VAC, ii) determine whether there is a significant difference in the isotopic signature of plant water extracted by VAC from lignified samples with and without bark, iii) compare the isotopic composition of plant water extracted by VAC and CVD.
The comparison tests were carried out in late March and early July 2024 on trees or shrubs of Cornus sanguinea, Carpinus orientalis, Prunus cerasifera, Photinia serratifolia, and Populus canadensis, located in a village close to Padua (Italy). In March, samples were taken from lignified twigs, and we prepared replicates with and without bark for extraction by VAC. In July, twig samples were collected for extraction by VAC and by CVD. Given the negligible presence of organic contaminants in VAC samples, we performed their isotopic analysis by laser spectroscopy. Conversely, CVD samples were analysed by isotope-ratio mass spectrometry.
Our results showed no significant differences in the sugar levels of samples with and without bark, and no clear relation between the sugar content and the isotopic composition of plant water extracted by VAC. Additionally, when comparing CVD and VAC, the δ18O values were similar, but there were significant differences in the δ2H between the two methods, with VAC samples plotting significantly closer to the Local Meteoric Water Line compared to CVD samples. These first results indicate that VAC is a promising and effective method for the extraction of plant water for isotopic analysis. However, further tests should be performed for other species and under different environmental conditions.
Acknowledgements: This study was carried out within the Agritech National Research Center and received funding from the European Union Next-Generation EU (PIANO NAZIONALE DI RIPRESA E RESILIENZA (PNRR) – MISSIONE 4 COMPONENTE 2, INVESTIMENTO 1.4 – D.D. 1032 17/06/2022, CN00000022). This abstract reflects only the authors’ views and opinions, neither the European Union nor the European Commission can be considered responsible for them.
How to cite: Zuecco, G., Todini-Zicavo, D., Aarts, E. J., and Marchina, C.: Testing a new method for extracting plant water for isotopic analysis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18327, https://doi.org/10.5194/egusphere-egu25-18327, 2025.
Posters virtual: Thu, 1 May, 14:00–15:45 | vPoster spot A
EGU25-9556 | ECS | Posters virtual | VPS10
Unravelling Sampling Bias in δ¹³C Isotope Variability in Coffee-Banana Intercropping for Drought Stress AssessmentThu, 01 May, 14:00–15:45 (CEST) | vPA.15
Coffee-banana intercropping, widely practiced by smallholder farmers in South America and East Africa, is recognized for its potential to combine sustainability with resilience to climate change. This practice promotes crop diversification, but may also enhance water-use efficiency. However, its effectiveness may vary depending on the local conditions and agricultural practices. The lack of quantitative data on drought stress and the complexity of interactions within coffee-banana intercropping systems pose significant challenges in modelling and optimizing water use efficiency. This study aims to develop and refine innovative methods to assess drought stress in coffee-banana intercropping systems, with a focus on stable carbon isotope values (δ¹³C), leaf temperature, and mid-infrared spectroscopy (MIRS). While stable carbon isotope analysis is a promising tool, its application may face challenges due to factors such as crop size, canopy heterogeneity, banana-coffee canopy overlapping, leaf age, orientation, or position (leaf morphological aspects), leading to variable competition for water and light. These factors affect the way sampling for stable carbon isotope and leaf temperature analysis should be conducted, in addition to physiological differences between coffee genotypes, agronomic practices, and complexities in data interpretation. Sampling and analytical protocols must be adapted to address these factors and their effects, while accounting for leaf morphology and microenvironmental parameters. Initially, we evaluated the influence of these factors on δ¹³C variability in coffee leaf samples, in addition to their correlation with leaf temperature. Samples were collected from a 0.15 hectares experimental farm managed by the Agricultural Research Company of Minas Gerais (EPAMIG) in Brazil, an intercrop of Arabica coffee and Cavendish banana plants at 3.6 a distance apart. Coffee leaves were sampled using a metal puncher and leaf temperature was measured using an infrared thermometer, considering varying levels of sunlight exposure. Ten plants of the Catuaí Vermelho IAC 44 coffee cultivar were randomly selected: five under conventional management (chemical fertilizers) and five under organic management (cattle manure). For each plant, samples were taken at three different heights (Top, Middle and Bottom), three orientations (South, East and West), and two branch sides, including young and mature leaves, resulting in 36 leaves per plant. The poster presents key findings on the variability of δ¹³C isotopes in coffee leaves within a banana-coffee intercropping system and their relationship with leaf temperature under different management practices (organic and conventional). This presentation highlights the observed effects of leaf sampling parameters, such as age, position, and sunlight exposure, on δ¹³C values, as well as the implications for improving drought stress screening methodologies.
How to cite: Bernardo, T., Vezzone, M., Felizardo, J. P., Rodrigues, C., Moura, W., Gomes Soares, L., Sebastião Sant' Anna Andrade, H., Victor Vieira Queiroz, C., Nakamya, J., Vantyghem, M., Dercon, G., and Meigikos dos Anjos, R.: Unravelling Sampling Bias in δ¹³C Isotope Variability in Coffee-Banana Intercropping for Drought Stress Assessment, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9556, https://doi.org/10.5194/egusphere-egu25-9556, 2025.
EGU25-14282 | ECS | Posters virtual | VPS10
Seasonal transpiration source water and ecohydrological connectivity with streamflow sources in the Maimai M8 CatchmentThu, 01 May, 14:00–15:45 (CEST) | vPA.16
Transpiration significantly depletes terrestrial subsurface water stores and plays a crucial role in
the hydrological cycle. While extensive research has been conducted in the Maimai M8 catchment
(New Zealand) and across many catchments on streamflow generation processes and streamflow
sources, we still know little about the sources of transpiration and when transpiration and
streamflow sources are hydrologically connected. Here we leverage M8, a long-term studied
catchment with well-described streamflow generation mechanisms, to investigate the transpiration
source water of Pinus radiata and its connectivity to streamflow sources. We combined monthly
observations of isotopic signatures (δ18O and δ2H) of xylem, bulk soil water, mobile water,
subsurface flow, and stream water with continuous monitoring of tree water stress across a
hillslope to answer: (1) What is the seasonal source of transpiration at Maimai? And (2) how does
transpiration source water interact with streamflow sources? Our data showed that transpiration
sources across the hillslope were not distinct but changed seasonally. During summer, when trees
showed greater periods of water stress, trees relied on shallow soil water. In contrast, during the
winter, trees’ isotopic signatures plotted along the local meteoric water line (LMWL), overlapping
with mobile soil and stream water. Xylem isotopic signatures were not statistically distinct from
stream signatures in the winter, contrasting with distinct isotopic signatures during the summer.
Our results showed that transpiration source water in the Maimai M8 catchment changes
seasonally, influenced by tree water stress and wetness conditions. Overall, our findings suggest
an ecohydrological connectivity between transpiration and streamflow sources during winter
months in this wet temperate climate.
How to cite: Simmons, C., Dudley, B., McDonnell, J., and Nehemy, M.: Seasonal transpiration source water and ecohydrological connectivity with streamflow sources in the Maimai M8 Catchment , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14282, https://doi.org/10.5194/egusphere-egu25-14282, 2025.
