HS10.8 | Stable isotopes to study water and nutrient dynamics in the soil-plant-atmosphere continuum
Stable isotopes to study water and nutrient dynamics in the soil-plant-atmosphere continuum
Convener: Marius Floriancic | Co-conveners: Natalie Orlowski, Giulia Zuecco, Magali Nehemy, Jesse Radolinski
Orals
| Thu, 18 Apr, 14:00–15:45 (CEST)
 
Room 2.15
Posters on site
| Attendance Wed, 17 Apr, 10:45–12:30 (CEST) | Display Wed, 17 Apr, 08:30–12:30
 
Hall A
Orals |
Thu, 14:00
Wed, 10:45
Stable isotopes are powerful tools for tracing water fluxes and associated nutrients in the soil-plant-atmosphere continuum. Ever new methodological developments allow measurements at high spatial and temporal resolution and interpretation of the complex interactions between subsurface water fluxes, plant water uptake and atmospheric drivers. We welcome experimental and modelling studies that present methodological developments and applications of isotope tracers to improve our process knowledge of water and nutrient fluxes between the subsurface, plants and the atmosphere, across different scales (from plant and forest stand up to the catchment scale). In our session, we aim to discuss i) innovative process-based interpretations from stable isotope data, ii) novel methods of model applications and data analysis, as well as iii) current methodological developments. We aim to foster interdisciplinary exchange between the various fields assessing ecohydrological processes using natural tracers, including research in groundwater and vadose zone hydrology, plant physiology, and ecology.

Orals: Thu, 18 Apr | Room 2.15

Chairpersons: Marius Floriancic, Giulia Zuecco
14:00–14:05
14:05–14:15
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EGU24-12264
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solicited
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Highlight
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On-site presentation
James Kirchner

Stable isotopes are essential tools for tracing water and nutrient fluxes in terrestrial ecosystems.  In recent years, studies of the soil-plant-atmosphere continuum have yielded impressive volumes of stable isotope tracer data at previously unattainable precision and spatiotemporal resolution.  These emerging data sets facilitate new methods of analysis that promise new insights into transport, storage and mixing.  For decades, end-member mixing analysis (EMMA) has been the standard workhorse for interpreting tracer data, but new methods can overcome some of its limitations and facilitate new inferences into ecosystem processes. 

 

At the catchment scale, for example, end-member mixing has been widely used to quantify streamflow as a mixture of isotopically distinct sources, but knowing where streamwater comes from is not the same as knowing where precipitation goes, for which one needs end-member splitting (Kirchner and Allen, 2020) instead.  End-member splitting allows summer and winter precipitation to be partitioned between evapotranspiration, summer streamflow, and winter streamflow, without direct measurements of evapotranspiration water fluxes or their isotopic composition. 

 

At the hillslope and plot scale, end-member mixing has been widely used to quantify the relative contributions of isotopically distinct sources to soils and xylem waters.  If any end-members are missing or their tracer distributions overlap, however, conventional mixing models become unusable.  These constraints can be overcome by exploiting the information contained in tracer time-series using ensemble end-member mixing analysis (EEMMA; Kirchner, 2023).  EEMMA can potentially quantify many sources using a single tracer, even if their mean concentrations are indistinguishable. EEMMA can also quantify source contributions when some sources are unknown, and even infer the tracer time series of a missing source. 

 

These new methods will be demonstrated using benchmark data, and proof-of-concept applications will be presented.

How to cite: Kirchner, J.: New methods for studying the soil-plant-atmosphere continuum with stable isotope data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12264, https://doi.org/10.5194/egusphere-egu24-12264, 2024.

14:15–14:25
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EGU24-11966
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On-site presentation
Bing Si, Eric Si, and Han Fu

Stable isotopes of hydrogen and oxygen in water are common tools for investigating water uptake apportionment, but many of the existing methods rely on simple linear mixing approaches that do not mechanistically incorporate additional information about site physical properties and conditions. Here, we develop a 'physically based root water uptake isotope mixing estimation' model (PRIME) that combines a continuous and parametric probability density function for root water uptake with site physical data in a process-based linear mixing framework. To demonstrate the application of PRIME, water uptake patterns of boreal forest Pinus banksiana trees were estimated on four dates in 2019. To aid in validation, estimates were compared with that of the Bayesian linear mixing model framework, MixSIAR. The two approaches provided similar results, but due to its continuous and parametric nature, PRIME provided estimates of superior resolution, certainty, and model parsimony. Although both models incorporate additional physical information into their mixing frameworks , PRIME does so in a mechanistic manner, thereby reflecting the relevant hydrological processes more effectively than the purely empirical approach taken by MixSIAR. Furthermore, because PRIME uses a continuous function to describe the predicted uptake pattern, it allows users to quantify water uptake with essentially infinite resolution, through integration over the desired depth ranges. These findings demonstrate the advantages of utilizing a continuous, parametric, and process-based mixing model to estimate root water uptake apportionment, thus providing a relatively simple yet powerful tool with which to approach plant water sourcing. 

How to cite: Si, B., Si, E., and Fu, H.: A process-based water stable isotope mixing model for plant water sourcing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11966, https://doi.org/10.5194/egusphere-egu24-11966, 2024.

14:25–14:35
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EGU24-383
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ECS
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Highlight
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On-site presentation
Maria Magdalena Warter, Dörthe Tetzlaff, Christian Marx, and Chris Soulsby

In urbanized areas the natural flow paradigm from river management is being increasingly challenged by hydroclimatic changes and marked anthropogenic influences on flow regulation. Although the impacts of urbanization, increased runoff and reduced baseflow are increasingly well quantified; the characteristics of flow regimes that are sustainable and wanted for urban streams to preserve or restore their hydrologic and ecological integrity in the face of future climate change and rapid urbanization, remain less well understood.

To that end, we conducted a paired catchment study of two streams, both sub-catchments of the Spree catchment – a more natural intermittent rural agricultural stream in Brandenburg (Demnitzer Mill Creek) and an anthropogenically impacted urban stream in Berlin (Panke).  We characterized contrasts in inter- and intra-annual streamflow variability, storm period responses, water ages and mixing processes. Through tracer-based analyses, using stable water isotopes, we identified the physical processes (sources, flow paths and age) sustaining stream flow over multiple years (2018-2023), and broadly linking them to biological dynamics obtained through environmental DNA, in order to estimate resilience to future hydroclimate interactions and land use changes. The higher specific discharge of the urban stream emerges as a clear artefact of artificially increased baseflow due to discharge of wastewater, while reacting primarily to convective summer storms with strong runoff reactions and short discharge peaks. In contrast, the rural stream shows a characteristically intermittent behavior with longer periods without baseflow and only limited runoff reactions with only temporary superficial accumulation of water after heavy rainfall. Water ages reflected the respective runoff contributions and mixing processes, with a low contribution of young water observed in the urban stream and a higher, more variable contribution of young water in the rural stream. The strong dichotomy of runoff responses and unmistakable influence of baseflow manipulation on streamflow dynamics and biological processes point to major uncertainties in the suitability of different approaches for the restoration of urban and management of naturally intermittent rivers. Effective stakeholder engagement will be necessary in seeking to manage flow regimes to maintain ecohydrological connectivity and future resilience in the face of urban growth and climate change.

How to cite: Warter, M. M., Tetzlaff, D., Marx, C., and Soulsby, C.: Characterizing changing stream flow components and hydroclimate interactions in cities – implications for future management and restoration of urban ecosystems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-383, https://doi.org/10.5194/egusphere-egu24-383, 2024.

14:35–14:45
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EGU24-6181
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ECS
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On-site presentation
Oludare Durodola, Youri Rothfuss, Cathy Hawes, Jo Smith, Tracy Valentine, and Josie Geris

Agricultural co-cropping, which is the cultivation of two or more crops simultaneously on the same field, is gaining rapid attention in temperate agroecosystems as a viable nature-based solution to improve agricultural productivity. However, relatively little is known about plant water use patterns in temperate agricultural co-cropping systems. Specifically, the functioning and resilience of these systems compared to their equivalent monocultures is likely to depend on whether water use is complementary for the different crops and how this might change during the growing season and under different hydro-climatological conditions.

This study focused on addressing these knowledge gaps by using water stable isotopes to trace the sources of vegetation water uptake (shallow or deep soil water) in 5 different cereal-legume co-cropping systems and 4 of their respective cereal monocultures under field conditions in North-East Scotland. For each treatment, we extracted vegetation water, and soil water from 5 different depths for analysis of isotopic composition. We then performed MixSIAR end-member mixing modelling to explore proportional water uptake patterns for cereal vegetation throughout the growing season and under wet and dry conditions.

The results showed that cereals in all the monocultures and co-cropping systems predominantly used shallow soil water (upper 5 cm), regardless of growth stage and hydro-climatological conditions. Cereal water uptake patterns in monocultures and co-cropping systems were comparable during wet hydrological conditions. However, the analyses revealed that cereals in co-cropping systems exhibited plasticity and increased their water uptake up from deeper soil water (5 – 30 cm) compared to cereals in monocultures during dry conditions. Furthermore, during dry conditions, we found different seasonal responses in the co-cropping systems between cereal genotypes traits. Understanding of plant water use patterns for different cropping systems could inform the design of resilient and sustainable water management practices and agricultural policies. The plasticity observed in co-cropping systems could potentially contribute to optimised water use under climate change.

How to cite: Durodola, O., Rothfuss, Y., Hawes, C., Smith, J., Valentine, T., and Geris, J.: Using stable water isotopes to trace cereal water use in agricultural co-cropping systems under contrasting hydro-climatological conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6181, https://doi.org/10.5194/egusphere-egu24-6181, 2024.

14:45–14:55
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EGU24-15966
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ECS
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On-site presentation
Samuel le Gall, Dagmar van Duschoten, Adrian Lattacher, Mona Giraud, Moritz Harings, Paulina Deseano Diaz, Ahmet Sircan, Christian Poll, Guillaume Lobet, Mathieu Javaux, and Youri Rothfuss

Farmers are increasingly adopting practices that add more biodiversity to agro-ecosystems for improving crop yield level and stability. These practices include co-croping, that is the cultivation of different phenotypes (or cultivars) in the same field. However, we are missing clear criteria for the selection of the cultivars as well as a quantified assessment of the effect of the combination on water use and partitioning.

In our study, we proposed to focus on the association of two wheat cultivars having contrasted root systems. We further aimed at evaluating the effect of such an association on water flow by monitoring root water uptake vertical patterns from isotopic analyses.

In a control environment, we ran experiments on soil columns (silty-clay) (diam=11cm, height=80cm) each planted with two wheat cultivars (“shallow-rooted” vs “deep-rooted”) until ear emergence. Six different modalities were tested, i.e., 3 crop types (2 shallow-rooted individuals / 2 deep-rooted individuals / combination of 1 shallow-rooted individual and 1 deep-rooted individual) x 2 treatments (well-watered conditions or water stress). We repeated the experiment six times to test all the different modalities mentioned above in triplicate. Profiles of root water uptake (RWU) relative fractions were statistically evaluated (with a Bayesian mixture model) at cm to dm vertical resolution from soil water and transpiration flux isotope data non-destructively using gas-permeable membranes and gas chambers coupled to a laser spectrometer. Plants were also monitored physiologically during the experiment (e.g., leaf area, chlorophyll content, root architecture by magnetic resonance imaging) and destructively (e.g., above-ground and below-ground biomass, root area, stomatal density).

We will present our observations on how the RWU profile are affected by soil water status, wheat phenotype and associated plant identity. Surprisingly, the deep-rooted phenotype individuals - which uptake more water than the shallow-rooted individuals at soil depth between 40cm and 80cm under water deficit condition - are also the most physiologically sensitive (reduction in leaf area, significant change in shoot/root biomass ratio) at the first reproductive stages. On the field scale, this could have later a negative impact on the yield of the deep-rooted phenotype monoculture, but this should be moderate in co-cropping situations, where the sensitivity of the whole is lower.

How to cite: le Gall, S., van Duschoten, D., Lattacher, A., Giraud, M., Harings, M., Deseano Diaz, P., Sircan, A., Poll, C., Lobet, G., Javaux, M., and Rothfuss, Y.: Investigating the impact on water fluxes and physiological development of the combination of contrasted root wheat cultivars from isotopic analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15966, https://doi.org/10.5194/egusphere-egu24-15966, 2024.

14:55–15:05
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EGU24-15354
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On-site presentation
Elham R. Freund, Maurus Villiger, Marco M. Lehmann, Zhaoyong Hu, Katrin Meusburger, and Arthur Gessler

Transpiration fluxes from land to the atmosphere hinge significantly on the degree to which trees opt to open their stomata to trade off water for CO2. Yet, the terrestrial ecosystem response to the changes in the atmosphere (CO2, VPD, etc.) and the redistribution of water on land in an era of change are largely unknown. In addition, the effects of such long-term changes in trees’ adaptation strategies and resilience under short-term dry conditions are not yet fully understood. To address this issue we determined stable water isotopologues within a long-term (20-year) irrigation experiment in a drought-prone Scots pine-dominated forest in one of the driest areas of Switzerland, Pfynwald. Our sampling included plots with trees growing under naturally dry conditions (control), irrigated (from 2003 to present), and previously irrigated (irrigation stop; irrigated from 2003–2013; control condition since 2014). We have installed an in-situ high-frequency isotope measurement system in the field to sample stable water isotopologues (2H and 18O) in different soil depths, tree xylem, and in the atmosphere and to track tree water uptake dynamics at the control, irrigated, and irrigation stop plots. The sampling was complimented with manual extraction of soil and xylem water samples at the three treatment plots for isotope analysis in the lab. Our preliminary findings support the hypothesis that pine forests adjust their carbon allocation strategies during long-term wet periods, establishing a deeper rooting system to access deeper water sources. This adaptive mechanism enhances their resilience during short-term dry periods.

How to cite: R. Freund, E., Villiger, M., M. Lehmann, M., Hu, Z., Meusburger, K., and Gessler, A.: Scots pine response to short-term dry conditions after long-term soil moisture manipulation experiment  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15354, https://doi.org/10.5194/egusphere-egu24-15354, 2024.

15:05–15:15
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EGU24-19346
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ECS
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On-site presentation
Fabian Bernhard, Marco M. Lehmann, Arthur Gessler, and Katrin Meusburger

Soil-vegetation systems partition incoming precipitation into either the freshwater system ("blue water") or back to the atmosphere as evapotranspiration ("green water"). The isotope signatures of these fluxes are observed to be distinct. We investigate the partitioning of precipitation and illustrate one potential mechanism for this "apparent" isotopic fractionation of root water uptake by means of an isotope-enabled mechanistic water balance model [1].

Stable water isotope signatures were collected at a Swiss forest site dominated by beech trees (>60 cm DBH, 37m stand height) with a mean annual precipitation of ~1050 mm/year, at 800 m.a.s.l throughout two vegetation seasons. Up to bi-weekly samples of xylem and mobile soil water and six bulk soil water campaigns (down to 150 cm) were combined with continuous hydrometric measurements (down to 200 cm) to constrain modelled water fluxes such as preferential infiltration patterns and seasonal patterns of root water uptake.

During the model validation period in 2022, the model faithfully reproduced seasonal and vertical patterns in isotope signatures. The goodness of fits of time series showed δ18O RMSE smaller than 0.4‰ for mobile soil water at 50cm or 80cm or smaller than 1.0‰ for stem xylem water at breast height, while the goodness of fits of vertical profiles had δ18O RMSE smaller than 1.7‰ for bulk soil water profiles down to 150cm. Reduced soil water availability in the topsoil during the summer of 2021 led to a downward shift of the flux-weighted average water uptake depths of beech trees. However, while the relative contribution to water uptake of soil layers below 80 cm increased during the summer of 2021, their absolute contribution did not increase sufficiently to compensate the water missing in the topsoil layers where most roots are located. 

Modelled infiltration pathways and root water uptake illustrate how seasonal and vertical selectivity of root water uptake leads to distinct isotope signatures in the modelled green and blue water fluxes. This behaviour is obtained at this site without a two-domain representation of the soil domain nor preferential flow to deeper layers. Further, simulations with synthetic seasonal isotope patterns in precipitation demonstrate how this "apparent" fractionation factor depends on the timing of transpiration together with the seasonality of the precipitation isotope signature. In conclusion, this study highlights that the soil-vegetation system may fractionate heavier precipitation for the green water fluxes mainly because of the seasonal patterns in precipitation isotope signatures and transpiration rates.

[1] Fabian Bernhard. (2024). fabern/LWFBrook90.jl: v0.9.8 (v0.9.8). Zenodo. https://doi.org/10.5281/zenodo.10463109

How to cite: Bernhard, F., Lehmann, M. M., Gessler, A., and Meusburger, K.: How beech trees use isotopically heavier precipitation because of seasonality, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19346, https://doi.org/10.5194/egusphere-egu24-19346, 2024.

15:15–15:25
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EGU24-19455
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ECS
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Highlight
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On-site presentation
Christina Hackmann, Sharath Paligi, Martina Mund, Dirk Hölscher, and Christian Ammer

Trees are major regulators of the forest water balance. To stay vital, water loss via transpiration has to be compensated by root water uptake. However, it is often not clear where exactly the trees get their water from. This has become particularly relevant in central Europe, as forests are facing more frequent and intense droughts with climate change. It is known that water uptake strategies are species-specific, influenced by environmental conditions and, potentially, neighboring species. Yet, knowledge about species-specific patterns of water uptake depth and how it is affected by tree-species mixture is scarce. Stable water isotopes present a valuable tool to elucidate these belowground processes.

For our study, we selected mixtures of European beech (Fagus sylvatica), the dominant broadleaved tree species in central Europe, with native, but drought-prone Norway spruce (Picea abies), and non-native, but supposedly more drought-resistant Douglas fir (Pseudotsuga menziesii), as well as the respective pure stands. We aimed to uncover the effect of (1) species identity, (2) species mixture and (3) environmental conditions on water uptake depth.  

To achieve this, we conducted two sampling campaigns in climatically contrasting years: a natural abundance campaign in relatively wet 2021, covering 20 plots on 4 sites, and a tracer experiment focused on European beech and Douglas fir on a subset of plots, including weekly sampling of 12 trees throughout the drought summer 2022. 

We found species-specific patterns of water uptake depth, where Norway spruce tended to use the greatest share of shallow water, followed by European beech and Douglas fir. Within species, the data indicated differences in water uptake depth between pure and mixed stands, however, we did not detect a spatial differentiation between co-occurring species. Dry conditions tended to shift water uptake to deeper layers, with beech responding stronger than Douglas fir.

Our results corroborate that species-specific traits have to be considered when assessing forest water pathways, especially in mixed forests and under drought. Considering central Europe, our data supports the assumption that Douglas fir may be more drought resistant than Norway spruce by tapping deeper water sources. In mixture, both European beech and Douglas fir seem to exploit similar soil depths, while none of the species is limited to the drought-prone topsoil.      

How to cite: Hackmann, C., Paligi, S., Mund, M., Hölscher, D., and Ammer, C.: Water uptake depth of European beech, Douglas fir and Norway spruce – species-specific patterns, seasonal dynamics and mixture effects, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19455, https://doi.org/10.5194/egusphere-egu24-19455, 2024.

15:25–15:35
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EGU24-14819
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Highlight
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On-site presentation
Katrin Meusburger, Josie Geris, Daniele Penna, Youri Rothfuss, Ilja van Meerveld, and Marco Lehmann

The COST Action WATer isotopeS in the critical zONe (WATSON; https://watson-cost.eu/) aims to elucidate the interactions between groundwater recharge, soil water storage, and vegetation transpiration across various climatic settings. Within this framework, root water uptake by trees is crucial for understanding water partitioning and forest resilience to drought. While isotopic approaches have successfully revealed root water uptake strategies for different species, a comprehensive assessment across different climates and vegetation types is still missing (Beyer and Penna, 2021).

To address this research gap, we executed a synchronized, participatory sampling campaign by WATSON Action members in late spring and summer of 2023. Soil and vegetation samples were taken across 39 well-distributed forest sites encompassing 17 European countries. The samples were analyzed for the stable isotopes of oxygen and hydrogen at the WSL laboratory in Switzerland. The data enable us to investigate the spatial and temporal (spring vs summer) variability of root water uptake of the shallower-rooted spruce (Picea abies) and deeper-rooted beech (Fagus sylvatica) trees. We expect beech to exhibit a more pronounced shift to deeper water sources during summer than spruce due to its deeper rooting system. We also expect that the dominant root water uptake depth is influenced by site-specific factors (climate, elevation, latitude, soil type, level of understory cover) and tree characteristics (tree height, stem diameter). This presentation will describe the sampling campaign and the preliminary results on root water uptake for both species across Europe.

How to cite: Meusburger, K., Geris, J., Penna, D., Rothfuss, Y., van Meerveld, I., and Lehmann, M.: Investigating Large-Scale Variation in Plant Water Uptake Across European Climates and Vegetation Types – a WATSON Cost Action Initiative, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14819, https://doi.org/10.5194/egusphere-egu24-14819, 2024.

15:35–15:45
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EGU24-8308
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ECS
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solicited
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Highlight
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On-site presentation
Ginevra Fabiani, Julian Klaus, Laurent Pfister, and Daniele Penna

The ongoing climate change is significantly impacting forest ecosystems, intensifying environmental extremes such as droughts and heatwaves. The increased atmospheric evaporative demand, coupled with reduced soil water availability, poses a risk of water deficit to trees, threatening their health status. These extremes can amplify the thermal and hydrologic gradients along hillslopes, driving spatially variable thermal and hydraulic stress for trees. Until now, site-specific case studies have offered only a limited understanding of how hydrological processes at the hillslope scale influence tree water use. Comparative studies hold the potential to offer a more generalized understating of how trees growing in complex terrains respond to spatially varying growing conditions.

To address this, we set up a comparative study on two forested hillslopes located in the Weierbach catchment (Luxembourg) and the Lecciona catchment in Tuscany (Italy), respectively. The investigated sites differ in steepness, climate, geology, and soil characteristics, but both are dominated by beech (Fagus sylvatica L.) trees. We combined sap velocity, isotope measures, and wood moisture content with environmental monitoring (soil moisture, groundwater level, and hydro-meteorological variables) at different locations to capture beech trees’ water response to heterogeneous environmental conditions. This combination of measurements allowed us to link the transpiration response of trees to water availability along the two investigated hillslopes over the 2019 and 2020 growing seasons in the Weierbach catchment and over the 2021 growing season in the Lecciona catchment.

We observed that surface topography and hillslope structure result in differing sap velocities in response to environmental controls (i.e., vapor pressure deficit and relative extractable water), but not consistently across our study sites. In the Weierbach catchment, we noted a uniform physiological response to environmental controls among trees, even during the drier conditions of 2020, compared to 2019. We attribute this consistency to the homogeneous growing conditions across the slope. On the contrary, in the Lecciona catchment, trees located upslope displayed a more conservative hydraulic behaviour compared to the footslope location. This finding suggests a stronger edaphic and environmental gradient across the hillslope topography. Here, water redistribution through shallow subsurface flow results in more favourable growing conditions and longer growing seasons for trees at the footslope location, compared to the rather uniform growing season observed in the Weierbach catchment. These contrasting results between the two investigated hillslopes suggest that in landscapes where the hydraulic and climatic gradients are stronger, the physiological response among locations will be more spatially variable.

How to cite: Fabiani, G., Klaus, J., Pfister, L., and Penna, D.: The influence of topography on beech water use: evidence from a comparative study, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8308, https://doi.org/10.5194/egusphere-egu24-8308, 2024.

Posters on site: Wed, 17 Apr, 10:45–12:30 | Hall A

Display time: Wed, 17 Apr, 08:30–Wed, 17 Apr, 12:30
Chairpersons: Marius Floriancic, Giulia Zuecco
A.88
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EGU24-12737
Giulia Zuecco, Alessio Gentile, Paolo Nasta, Stefano Brighenti, Carolina Allocca, Giacomo Bertoldi, Davide Canone, Francesco Comiti, Ginevra Fabiani, Stefano Ferraris, Francesca Manca di Villahermosa, Chiara Marchina, Fabio Marzaioli, Daniele Penna, Maurizio Previati, Nunzio Romano, Luisa Stellato, Diego Todini-Zicavo, and Marco Borga

Stable isotopes of hydrogen and oxygen are useful tracers for investigating the water sources exploited by plants for transpiration. Recent studies focused on the analysis of the temporal origin of soil and xylem water, and showed that many plant species, during the growing season, tend to take up water originating from winter rainfall events. However, the climate and biophysical factors controlling the temporal origin of soil and xylem water are still unclear. Given this background, this study aims to i) evaluate the seasonal origin of soil and xylem water by using the so-called Seasonal Origin Index (SOI), and ii) investigate the climate drivers and biophysical controls influencing the seasonal origin of xylem water.

For this, we used isotopic data in precipitation, soil and xylem water along an Italian climate and topographic transect, including four Alpine and pre-Alpine catchments (Dora del Nivolet, Grangia dell'Alpe, Matsch/Mazia, and Ressi) in northern Italy, and two Apennine catchments in central (Re della Pietra) and southern Italy (Gorga). Soil samples at different depths up to a maximum depth of 1 m and vegetation samples were collected fortnightly during the growing seasons in the period 2020-2022, whereas bulk precipitation was collected fortnightly or monthly throughout the year. Vegetation samples included lignified twigs or wooden cores from different tree species (i.e., beech, chestnut, and larch) as well as roots from shrub species typical of Alpine grasslands.

 

The dual-isotope plot evidenced a marked isotopic variability in water samples among the different sites, particularly for precipitation. Soil water reflected the seasonal variability observed in precipitation in all study sites, although the isotopic signal was affected by evaporative processes, particularly marked in the shallow soil layers. The isotopic composition of xylem water showed that in most study areas these samples had predominantly a spring and summer origin, except for soil and xylem water in the two Apennine catchments which had a strong winter (Re della Pietra) and summer origin (Gorga). So far, no clear relations between the average SOI for soil water and xylem water and climatic indicators (e.g., rainfall seasonal index) were detected. Further analyses will include other indicators which better characterize vegetation characteristics, soil properties, and terrain features.

 

Keywords

Xylem water, soil water, stable isotopes of hydrogen and oxygen, seasonal origin index

How to cite: Zuecco, G., Gentile, A., Nasta, P., Brighenti, S., Allocca, C., Bertoldi, G., Canone, D., Comiti, F., Fabiani, G., Ferraris, S., Manca di Villahermosa, F., Marchina, C., Marzaioli, F., Penna, D., Previati, M., Romano, N., Stellato, L., Todini-Zicavo, D., and Borga, M.: Investigating the seasonal origin of soil and xylem water in Italian mountain catchments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12737, https://doi.org/10.5194/egusphere-egu24-12737, 2024.

A.89
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EGU24-21290
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ECS
Harsh Beria, Marius G. Floriancic, and James W. Kirchner

The hydrologic cycle in Switzerland relies on inputs from winter precipitation, whereby snowmelt plays an important role replenishing soil water, streams and aquifers. Previous studies found that plant water uptake during the summer growing season is dominated by winter precipitation. Here we use stable water isotope data of xylem and soil water from four experimental catchments and from two snapshot sampling campaigns during the growing season to assess what drives seasonal patterns in xylem water signatures.

We unveil divergent trends in the seasonal origin of waters used by trees compared to water flowing into nearby streams and aquifers. In low-elevation catchments characterized by little snowfall, summer precipitation predominantly refills streams and aquifers, while winter precipitation feeds vegetation water uptake. Conversely, higher-elevation catchments exhibit an opposite pattern, where winter precipitation primarily recharges streams and aquifers, and vegetation water uptake is driven by summer precipitation. We propose a theoretical framework to elucidate the divergence in vegetation water uptake from stream and groundwater recharge. This framework offers insights into the intricate relationships governing water availability in terrestrial ecosystems in different elevations across the Swiss Alps.

How to cite: Beria, H., Floriancic, M. G., and Kirchner, J. W.: Seasonality of tree water uptake explained by amount and timing of soil water refill, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21290, https://doi.org/10.5194/egusphere-egu24-21290, 2024.

A.90
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EGU24-759
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ECS
Maurus Nathanael Villiger and Elham Freund

The isotopic composition of water in plant xylem in comparison to the soil water isotopic composition is often used to investigate the plant water uptake patterns (e.g., Gessler et al. 2022), drought effects on plants (e.g., Lehmann et al. 2023, in review) and the water exchange through the river, soil, vegetation and atmosphere continuum (e.g., Brooks et al. 2010). Several studies have shown that there is a difference in the isotopic composition between the water source and the xylem water in trees. However, the source of this difference is subject to current scientific debates. Two-water-world hypothesis (Brooks et al. 2010), fractionation during root-water uptake (Vargas et al. 2017), bias due to cryogenic water distillation (Chen et al. 2020; Barbeta et al. 2022), Fractionation during movement of water between different tree tissues (Barbeta et al. 2022) are among the hypotheses proposed in the literature as the origin of the isotopic difference between source water and xylem water. 

Here we used several water extraction and isotope analysis methods to shed light on the isotope-based methods in tracking water movement in the soil-vegetation-atmosphere continuum. Our study site is a scots pine forest stand in the long-term drought experimental site, Pfynwald, Switzerland where the forest is exposed to a range of moisture conditions by irrigation.  

To extract xylem water, we used the Scholander Pressure Bomb, cryogenic vacuum distillation, and the vapor equilibrium method. For the soil water extraction, the equilibrium vapor extraction and cryogenic vacuum distillation method is used for different depths. Furthermore, we used the isotope ratio laser spectrometer and isotope ratio mass spectrometer to analyse extracted water samples.

With this work, we aim to answer the following questions: a) Is there a difference in the isotopic composition of water extracted with the equilibrium vapor method (in-situ, bulk stem water), Scholander pressure bomb (sap flow water) and the cryogenic vacuum distillation method (bulk stem water)? b) How are the observed isotopic differences between xylem and soil water related to the available moisture conditions?

 

References

Barbeta et al. (2022). Evidence for distinct isotopic compositions of sap and tissue water in tree stems: consequences for plant water source identification. https://doi.org/10.1111/nph.17857.

Brooks et al. (2010). Ecohydrologic separation of water between trees and streams in a Mediterranean climate. https://doi.org/10.1038/ngeo722.

Chen et al. (2020). Stem water cryogenic extraction biases estimation in deuterium isotope composition of plant source water. https://doi.org/10.1073/PNAS.2014422117.

Gessler et al. (2022). Drought reduces water uptake in beech from the drying topsoil, but no compensatory uptake occurs from deeper soil layers. https://doi.org/10.1111/nph.17767.

Lehmann et al. (2023, in review). Hydrogen isotopes in leaf and tree-ring organic matter as potential indicators of drought-induced tree mortality. https://doi.org/10.22541/AU.168167196.63741053/V1.

Vargas et al. (2017). Testing plant use of mobile vs immobile soil water sources using stable isotope experiments. https://doi.org/10.1111/nph.14616.

How to cite: Villiger, M. N. and Freund, E.: Forest Water Uptake Dynamics in the Long-Term Drought Experimental Site, Pfynwald – Intercomparison of Water Extraction and Isotope Analysis Methods, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-759, https://doi.org/10.5194/egusphere-egu24-759, 2024.

A.91
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EGU24-20559
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ECS
Understanding increases in tree growth by hydropower development using tree-ring carbon and oxygen stable isotopes
(withdrawn after no-show)
Lian Sun and Yesi Zhao
A.92
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EGU24-9015
Christophe Hissler, Julian Klaus, François Barnich, Cédric Guignard, Loïc Louis, Giulia Zuecco, and Nicolas Angeli

The stable isotopes of hydrogen and oxygen of the water molecule are widely used in ecohydrological-process studies to understand water uptake, redistribution by plants or to partition evaporation and transpiration. In this regard, within the last decade, the demands for a high spatio-temporal resolution of stable isotope data from xylem water has risen to better understand the water interactions between the Critical Zone compartments.

The arrival of isotope ratio infrared spectroscopy (IRIS) for analysing stable water isotopes based on the different adsorption spectra of water molecules with different isotopic composition allowed much faster sampling processing, in-situ measurements in the field, and lower costs per sample. Currently two IRIS instruments are available on the market with measurement technology based on i) off-axis integrated cavity output spectroscopy (OA-ICOS) and ii) wavelength scanned cavity ring-down spectroscopy (WS-CRDS). However, IRIS measurements of water samples can be seriously compromised by interference of some specific organic compounds in the sample with the absorption spectrum of water isotopologues. The impact of contamination issue by organic compounds on the IRIS measured isotopic composition has led to a range of measures to support usability of IRIS instruments in ecohydrological studies.

Until recently isotope ratio mass spectrometry (IRMS) was the standard in isotope hydrology studies and it is still considered as the reference in ecohydrology to mitigate the effects of organic contamination. However, IRMS analysis of water samples include the oxygen and hydrogen isotopes of organic compounds that are present in the water before entering the furnace of the spectrometer. Those compounds are burned at the same time as the oxygen and hydrogen of the water molecule and can dissipate together with those resulting in joint signal detection in the mass spectrometer analysis. This contribution to the measured oxygen and hydrogen isotopic composition from the organic compounds has the potential to compromise the IRMS results depending on the concentration, species, and the isotopic composition of the organic compounds present in the water sample.

In this study, we assess the type and concentration of organic compounds in extracted xylem water and evaluate their impact on stable water isotope analysis with IRMS and IRIS. Our working hypothesis is that samples that are currently analysed in ecohydrology, such as xylem samples heavily enriched in organic compounds, decrease more the analytical precision of IRMS than that of IRIS. We perform an intercomparison study between IRMS and two IRIS instruments with different configurations (with and without combustion module; old and new catalyst) on water without organic compounds, water spiked using different organic molecules (glucose, ethanol, methanol) and beech sap samples.

How to cite: Hissler, C., Klaus, J., Barnich, F., Guignard, C., Louis, L., Zuecco, G., and Angeli, N.: A comparative study to analyze O and H water isotopes in organic enriched solutions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9015, https://doi.org/10.5194/egusphere-egu24-9015, 2024.

A.93
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EGU24-17277
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ECS
Katya Dimitrova-Petrova, Christine Stumpp, Lena Scheiffele, Karoline Kny, and Sascha Oswald

Improving groundwater recharge flux (GWR) estimation is key for effective or sustainable groundwater resource management. Yet, GWR assessment is challenging as direct measurements are usually limited to the point scale and specific depths of the vadose zone . In agricultural settings, the spatial variability introduced by land use management may further complicate the assessment. Tracer studies in the vadose zone, combining stable isotopes (δ2H and δ18O) in soil water and water storage measurements can aid such assessment in agriculturally managed landscapes. The stable water isotope signal can provide insights into the timing of the soil water transport while traditional water storage measurements (i.e. soil moisture, groundwater levels) can provide complementary information allowing for comparison or alignment.

In this study, we aim to provide an integrative estimate of GWR under various agricultural land covers at the field scale. For that, we combine dedicated measurements of soil water stable isotope and continuous water storage observations spanning the soil profile from topsoil to groundwater table. The study was conducted in a highly instrumented research site near Potsdam, Brandenburg, situated on a gentle hillslope and covered by a variety of agricultural plots.

During two sampling campaigns in spring (May) 2023 and winter (January) 2024, we collected bulk soil water from various soil profiles (0-150 cm) along with monthly groundwater samples and analysed them for stable water isotopes (δ2H and δ18O). By integrating isotope data with soil moisture observations, we trace GWR using the peak shift method. Complementary GWR estimates are derived from timeseries of tensiometers and groundwater level fluctuations.

We present an overview of the experimental set up and preliminary GWR estimates. Our aim is to offer a complementary perspective on the key processes governing vertical water fluxes within the vadose zone across different depths, land covers, and hillslope positions, advancing our understanding of GWR dynamics at this managed agricultural site.

How to cite: Dimitrova-Petrova, K., Stumpp, C., Scheiffele, L., Kny, K., and Oswald, S.: Groundwater recharge quantity and timing across land covers in a managed agricultural landscape in NE Germany: insights using stable water isotope approaches and water storage measurements, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17277, https://doi.org/10.5194/egusphere-egu24-17277, 2024.

A.94
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EGU24-13937
Kegan Farrick, Josie Geris, Priya Ramjohn, Oludare Durodola, and Jeffrey McDonnell

In cocoa agroforesty systems, shade trees are used to create climate conditions that benefit cocoa growth and survival. However, the benefits may be offset by competition between shade trees and cocoa for water, especially in a changing climate.  Here we use stable isotope tracers to quantify  the patterns and depths of water uptake among shade timber trees, cocoa, and banana for a tropical agroforestry system in Trinidad. Rainfall was collected from August 2021 to September 2023. Three field campaigns were carried out at an upslope and downslope location representing different hydro-climatological conditions and at different times in the crop cycle. During each campaign and at each slope position, soil was collected from three pits at depths of 5, 15, 25, 50 and 75 cm below the surface, while up to 10 xylem cores were collected from the different plant species. Additional soil texture and soil moisture data were also collected. Cryogenic vacuum extraction was used to extract water from the soil and vegetation samples, while an Elementar Isoprime isotope ratio mass spectrometer was used to determine the δ2H and δ18O of the extracted water. These data were subsequently used for MixSIAR endmember mixing modelling. Our results suggest that cocoa and banana plants primarily use shallow soil water (0 – 10 cm below the surface), while shade and timber trees like Immortelle (Erythrina poeppigiana) and Cedar (Cedrela odorata) use water from deeper sources (20 – 50 cm below the surface). Spatially, plants located in upslope areas appear to use water from slightly deeper soil depths than downslope locations. Soils in the valley bottom were also wetter and had relatively higher clay content. This study indicates that shade trees do not compete with cocoa for water; however, bananas likely compete with cocoa making managing that co-cropping important.

How to cite: Farrick, K., Geris, J., Ramjohn, P., Durodola, O., and McDonnell, J.: Tracing the complementary and competitive water use patterns in a Theobroma cacao (cocoa) agroforestry system: A stable isotope approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13937, https://doi.org/10.5194/egusphere-egu24-13937, 2024.

A.95
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EGU24-17534
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ECS
Janice Nakamya

IS SAMPLING INFLUENTIAL ON VARIATIONS IN 13C STABLE ISOTOPE WHILST SCREENING FOR DROUGHT STRESS IN COFFEE

           Janice Nakamya1,2, Roel Merks3, Rebbeca Hood-Nowtry2, Gerd Dercon1Jeremiah Mwangi4, Silas Makune4

1 Soil and Water Management & Crop Nutrition Laboratory, Joint FAO/IAEA Centre of Nuclear Techniques in Food and Agriculture, Department of Nuclear Sciences and Applications, International Atomic Energy Agency, 2444 Seibersdorf, Austria

2University of Natural Resources and Life Sciences Vienna, Peter-Jordan-Straße 82, 1190 Vienna

3 Division of Soil and Water Management, Faculty of Bioscience, KU Leuven, Kasteelpark Arenberg 20, 3001 Heverlee, Belgium

4 Kaweri Coffee Plantation, Plot 1 Kitemba 264, Mubende Uganda

An enormous coffee yield gap and subsequent decline in income has been realised from drought, triggering a need for faster screening tool for water stress and estimation of water use efficiency for the commonly grown coffee varieties. However, determining the critical thresholds of drought stress in perennial crops especially in coffee is challenging. Stable isotope measurement of coffee leaves could avail instantaneous measurements as they track the changes at leaf level, there has been limited use of isotopes to monitor drought stress in coffee. Furthermore, using punch leaf samples instead of bulk leaf samples would be faster and cheaper by eliminating grinding.  The method requires homogenous sampling to provide representative samples and ensure quality results, suggesting detailed understanding of variations in d13C at coffee leaf level.  The study was conducted on commonly grown 6 old clones’ varieties of Robusta coffee, each in a 16-year-old 15 by 15m trail plot at Kaweri Coffee plantation Mubende, Central Uganda. With a specific aim of establishing (1) Whether d13C varies within the different leaf ages, leaf symmetry and sample position on the leaf (Fig.1). Separate punch leaf samples were obtained on young fully grown, below, and old pair of leaves on the left and right side of the apex, middle and rare of the lamina.  The results reveal a significant variation in d13C between young and old leaves but not with the pair in between them. Furthermore, a leaf pair is not the same in terms of d13C but it does not matter which position on the leaf the punched sample is obtained from.  Implying, for the best representation, coffee punch sample would be from any position of an old leaf.   

How to cite: Nakamya, J.:  Is sampling influential on the variations in 13C stable isotopes whilst screening for drought stress in coffee?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17534, https://doi.org/10.5194/egusphere-egu24-17534, 2024.

A.96
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EGU24-9150
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ECS
Sabrina Santos Pires, Gernot Bodner, and Christine Stumpp

The impact of climate change on crop production, marked by increased drought and heat stress, poses significant challenges to agricultural productivity. To overcome these challenges, it is essential to understand how crops take up water through their roots. Sugar beet farming holds immense importance in Austria, especially in the eastern region, where limited water supply constrains crop production. Consequently, strategies need to be developed to enhance water resource utilization and improve plant resilience against drought for sustainable sugar beet production. Therefore, in controlled laboratory experiments, a new method was developed to determine the distribution of water uptake by plant roots in response to dry topsoil conditions and variations in root depth for different sugar beet cultivars. Stable water isotope techniques were used to trace labelled water in rhizobox experiments from the soil to plant transpiration. The water-vapor equilibration technique, commonly used for soil samples, was adapted to measure water-stable isotopes in transpired water on live plants. Leaves were placed in Ziploc bags, inflated with dry air, and allowed to stabilize for at least 16 hours. After equilibration, the bag was punctured, and the equilibrated air and transpired vapor were directed to a laser spectrometer for stable water isotope analysis (2H/1H, 18O/16O). These isotopic ratios provided insights into the depth of root water uptake, aiding in the selection of crop varieties with effective water extraction from deep soil layers. Results indicate that sugar beets develop long roots capable of taking up water from deeper soil layers and adjusting their water uptake mechanisms when topsoil water is scarce. In summary, this study explores the crucial issue of water uptake in sugar beet cultivation, particularly in the context of climate change and water limitations. The findings will inform more efficient agricultural practices, enhance crop resilience, and support sustainable water resource management.

How to cite: Santos Pires, S., Bodner, G., and Stumpp, C.: Uncovering Sugar Beet Water Uptake Through Stable Water Isotope Analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9150, https://doi.org/10.5194/egusphere-egu24-9150, 2024.

A.97
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EGU24-15927
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ECS
Mirco Peschiutta, Martina Tomasella, Giuliano Dreossi, Mauro Masiol, Barbara Stenni, Luca Zini, Carlotta Musso, Vittoria Posocco, Chiara Calligaris, Paolo Sivilotti, and Klemen Lisjak

Due to climate change, southern European viticulture will experience lower and more variable yields and an use of irrigation will be necessary. In the cross-border area between Italy and Slovenia, grapevines are also grown in karst environments on shallow soils developed over limestone bedrock. In this environment the use of irrigation is very limited due to the scarcity of water sources and the ruggedness of the terrain.

In the framework of the Interreg Ita-Slo Acquavitis project we conducted an ecohydrological investigation over two consecutive growing seasons on a Vitis vinifera cv. Refošk vineyard on a shallow (50 ÷ 100 cm) karstic red soil in Ceroglie (Friuli Venezia-Giulia, Italy) to: (I) understand the water dynamics in the soil, (II) monitor the vines water status and (III) assess the depth of root water uptake. We also investigated the possibility of vines to exploit water reserves in caves, fractures, and matrix of the karstic system. Monthly precipitations were sampled from July 2020 to December 2021, and single precipitation events from February 2021 to June 2022. A first sampling campaign for soil, xylem sap and water potentials was conducted in 2020, with three sampling dates during the summer. In the following season 2021, the second campaign was conducted with a sampling frequency of ca 15 days from March to October for soil and from June to September for xylem sap . Sampling of dripping water and cave-soil were carried out in a nearby cave up to a depth of approximately 7 m.

Oxygen and hydrogen stable water isotope composition was analysed in precipitation and dripping waters from the cave using an IRMS; an IRIS-IM technique was used to extract and analyse soil water and to analyse xylem sap extracted with a vacuum system in the field. We also measured soil water content, soil water potential,

Summer 2020 was particularly rainy while 2021 showed heavier rainfall in spring followed by a drier summer. Results from the soil water and xylem sap isotopic values suggested that in this vineyard the vines relied mainly on shallow (above 50 cm) water and precipitation of late spring and summer. Soil water isotopic data showed a high variability in the upper soil while below 40 cm the δ2H values varied by only 10‰, while xylem saps showed an even slighter variability. Cave-soil water isotopic values were within the variability range of the vineyard ones, as such we could not discriminate whether the vines used also this water resource matrices.

Based on the water potential data of the two growing seasons, the availability of water in the vineyard soil was sufficient for the vines and it seems unlikely that under similar conditions, water resources from the karstic system would be utilised. In the event of severe drought conditions, as occurred in 2022, however, these additional water resources could be exploited by the vines, contributing to a better resilience of the karstic vineyards.

How to cite: Peschiutta, M., Tomasella, M., Dreossi, G., Masiol, M., Stenni, B., Zini, L., Musso, C., Posocco, V., Calligaris, C., Sivilotti, P., and Lisjak, K.: Ecohydrological investigation of a karstic vineyard in Ceroglie (Italy)   , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15927, https://doi.org/10.5194/egusphere-egu24-15927, 2024.