Isotope labeling experiment to infer ecohydrological travel times

Stable water isotopes are promising tracers to study soil-tree interactions and root water uptake. Traditionally, destructive sampling techniques are applied to measure the isotopic signature in soils and plant tissues but these methods are limited in their temporal resolution. For calculating ecohydrological travel times from soil water to transpiration, high frequent isotope measurements are required. Recently, in-situ water isotope probes have been successfully applied in beech trees to yield high-frequent isotope measurements under field conditions but the complexity and heterogeneity of natural field conditions can make a systematical method testing difficult. Here, we test whether the new probes are capable of capturing tree species-specific differences in root water uptake and associated travel times. We test this in a controlled experiment using large pots with three 4-6 meter high and 20 year old coniferous and deciduous trees: Pinus pinea, Alnus x spaethii and Quercus suber that are expected to have different water uptake strategies. We applied deuterated irrigation water to the homogeneous soils in the pots and traced the water flux from the soils through the trees with in-situ isotope probes in high temporal resolution. This contribution presents preliminary results on ecohydrological travel times in relation to environmental parameters such as sap flow, photosynthetic activity, matrix potential, soil water content, water vapor pressure deficit and solar radiation. Our in-situ isotope probes were capable to capture the breakthrough of the isotope tracer in all trees. The calculated travel times were shorter for the Pinus and Alnus compared to the Quercus which suggests differences in root water uptake. Detailed results from such controlled experiments are fundamental for testing new measurement techniques such as the in-situ isotope probes. Such results are important to better interpret results measured under natural and therefore more complex and heterogeneous field conditions.

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Simulating soil-plant-atmosphere interactions for sub-daily in situ observations of stable isotopes in soil and xylem water to assess two-pore domain model hypothesis

10.5194/egusphere-egu2020-17975 ◽

2020 ◽

Author(s):

Fabian Bernhard ◽

Stefan Seeger ◽

Markus Weiler ◽

Arthur Gessler ◽

Katrin Meusburger

Keyword(s):

Stable Isotopes ◽

Soil Water ◽

Vadose Zone ◽

Model Performance ◽

Root Water Uptake ◽

In Situ Observations ◽

Pore Domain ◽

Model Structures ◽

Isotope Measurements

Recent advances in stable isotope measurements within the soil-plant-atmosphere continuum have paved the way to high-resolution sub-daily observations of plant water supply (Stumpp et al. 2018, Volkmann et al. 2016a, 2016b). It seems time is ripe for in-depth assessments of long-standing yet much-debated assumptions such as complete, homogenous mixing of water in the vadose zone (&#8220;one water world&#8221; versus "two water world") or absence of fractionation during root water uptake and vascular transport in plants.Information on the nature of these processes contained in high-resolution data sets needs to be exploited. One way to test hypotheses and thereby advance our understanding of soil-plant water interactions is by analysing observations with numerical simulations of the system dynamics &#8211; a method also known as inverse modelling. By evaluating the model performance and parameter identifiability of different model structures, conclusions can be drawn regarding the relevance of the modelled processes for reproduction of the observations. Testing two different models allows thus to assess the impact of the difference.We develop a framework for numerical simulation and model-based analysis of observations from soil-plant-atmosphere systems with a focus on isotopic fractionation. A central objective is to facilitate the evaluation of different model structures and thus test model hypotheses. This can assist development of models specifically tailored to the intended purpose and available data. The framework will first be tested with the "SWIS" model presented by Sprenger et al. (2018).As an illustration of the framework, we will test the model performance on a dataset of continuous, in situ observations of stable isotopes in xylem water of beech trees and soil water in four depths combined with observations of soil water content. The model assumes one-dimensional soil water flow taking place in one or two separate flow domains for tightly and weakly bound pore water. These two water pools are separated by a matrix potential threshold and isotopic exchange is modelled only through the vapour phase. Root water uptake is parametrised using the Feddes-Jarvis model. First results allow to assess the relevance of the two-pore domain hypothesis for the different soil depths and xylem water.&#160;Sprenger, M., D. Tetzlaff, J. Buttle, H. Laudon, H. Leistert, C.P.J. Mitchell, J. Snelgrove, M. Weiler, and C. Soulsby. 2018. Measuring and modeling stable isotopes of mobile and bulk soil water. Vadose Zone J. 17:170149. doi:10.2136/vzj2017.08.0149Stumpp, C., N. Br&#252;ggemann, and L. Wingate. 2018. Stable isotope approaches in vadose zone research. Vadose Zone J. 17:180096. Doi: 10.2136/vzj2018.05.0096Volkmann, T.H., K. Haberer, A. Gessler, and M. Weiler. 2016a. High&#8208;resolution isotope measurements resolve rapid ecohydrological dynamics at the soil&#8211;plant interface. New Phytologist, 210(3), 839-849.Volkmann, T.H., K. Haberer, A. Gessler, and M. Weiler. 2016a. High&#8208;resolution isotope measurements resolve rapid ecohydrological dynamics at the soil&#8211;plant interface. New Phytologist, 210(3), 839-849.

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Ecohydrological travel times derived from in situ stable water isotope measurements in trees during a semi-controlled pot experiment

Hydrology and Earth System Sciences ◽

10.5194/hess-25-4513-2021 ◽

2021 ◽

Vol 25 (8) ◽

pp. 4513-4530

Author(s):

David Mennekes ◽

Michael Rinderer ◽

Stefan Seeger ◽

Natalie Orlowski

Keyword(s):

Water Uptake ◽

Tree Species ◽

Sap Flow ◽

In Situ Measurements ◽

Travel Times ◽

Isotope Tracer ◽

Standard Deviations ◽

Isotope Measurements ◽

Water Isotope

Abstract. Tree water uptake processes and ecohydrological travel times have gained more attention in recent ecohydrological studies. In situ measurement techniques for stable water isotopes offer great potential to investigate these processes but have not been applied much to tree xylem and soils so far. Here, we used in situ probes for stable water isotope measurements to monitor the isotopic signatures of soil and tree xylem water before and after two deuterium-labeled irrigation experiments. To show the potential of the method, we tested our measurement approach with 20-year-old trees of three different species (Pinus pinea, Alnus incana and Quercus suber). They were planted in large pots with homogeneous soil in order to have semi-controlled experimental conditions. Additional destructive sampling of soil and plant material allowed for a comparison between destructive (cryogenic vacuum extraction and direct water vapor equilibration) and in situ isotope measurements. Furthermore, isotope-tracer-based ecohydrological travel times were compared to travel times derived from sap flow measurements. The time to first arrival of the isotope tracer signals at 15 cm stem hight were ca. 17 h for all tree species and matched well with sap-flow-based travel times. However, at 150 cm stem height tracer-based travel times differed between tree species and ranged between 2.4 and 3.3 d. Sap-flow-based travel times at 150 cm stem hight were ca. 1.3 d longer than tracer-based travel times. The isotope signature of destructive and in situ isotope measurements differed notably, which suggests that the two types of techniques sampled water from different pools. In situ measurements of soil and xylem water were much more consistent between the three tree pots (on average standard deviations were smaller by 8.4 ‰ for δ2H and by 1.6 ‰ for δ18O for the in situ measurements) and also among the measurements from the same tree pot in comparison to the destructive methods (on average standard deviations were smaller by 7.8 ‰ and 1.6 ‰ for δ2H and δ18O, respectively). Our study demonstrates the potential of semi-controlled large-scale pot experiments and very frequent in situ isotope measurements for monitoring tree water uptake and ecohydrological travel times. It also shows that differences in sampling techniques or sensor types need to be considered when comparing results of different studies and within one study using different methods.

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Inferring plant physiologic parameters for root water uptake modelling from high frequency in-situ isotope measurements

10.5194/egusphere-egu2020-22007 ◽

2020 ◽

Author(s):

Stefan Seeger ◽

Michael Rinderer ◽

Markus Weiler

Keyword(s):

Soil Moisture ◽

Water Uptake ◽

Root Distribution ◽

Fine Root ◽

Root Water Uptake ◽

Plant Water ◽

Plant Water Uptake ◽

Fine Root Distribution ◽

Isotope Measurements

In the face of global climate change, a well-informed knowledge of plant physiologic key parameters is essential to predict the behavior of ecosystems in a changing environment. Many of these parameters may be determined with lab or pot experiments, but it could prove problematic to transfer results obtained in a such experiments with small trees to fully grown trees. Therefore, new approaches to determine relevant parameters for mature trees are still required. Regarding plant water uptake, parameters related to fine root distribution (maximum depth, depth distribution and rhizosphere radius) and parameters describing the physiological limits of root water uptake are important, but usually hard or costly to assess for fully grown trees.&#160; In-situ isotope probes (Volkmann et al. 2016a&#160; & 2016b) are a promising recent development that offer new possibilities for the investigation of plant water uptake and associated physiological parameters.In this study we used in-situ stable water isotope probes in soil (six depths from 10 to 100 cm) and in tree xylem of mature (140 years) European beech trees (three heights between 0 and 8 m). With those probes, we monitored soil and xylem isotope signatures after an isotopically labeled (Deutrium-Excess = 100 &#8240;) irrigation pulse equivalent to 150 mm of precipitation and foursubsequent natural precipitation events over a period of twelve weeks with a high temporal resolution (six or more measurements per probe per day). Those measurements were complemented with measurements of soil moisture and sap flow dynamics. We interpolated our measured soil isotope and soil moisture data in order to obtain spatially and temporally continuous data for those soil parameters. Then we used this data as an input to the Feddes-Jarvis plant water uptake model, in order to predict the isotopic signature of plant water uptake at daily time steps. With the help of our observed isotopic signatures, we were able to directly constrain the critical water potential parameter of the Feddes model as well as the underlying fine root distribution. Furthermore, the observed dampening of the breakthrough curve of our Deuterium-labeling pulse allowed us to infer information on the rhizosphere&#160; radius and water transport velocities in the fine roots and stem between the points of root water uptake and the eight meter stem height.With our field experiment we showed that in-situ isotope measurements in soil profiles and in tree xylem sap can help to constrain plant water uptake modelling parameters. Future experiments might use this approach to scrutinize lab-scale derived hypothesizes regarding tree water uptake and to investigate the temporal and spatial dynamics of root water uptake in the field.&#160;Volkmann, T. H., Haberer, K., Gessler, A., & Weiler, M. (2016a). High&#8208;resolution isotope measurements resolve rapid ecohydrological dynamics at the soil&#8211;plant interface. New Phytologist, 210(3), 839-849.&#160;Volkmann, T. H., K&#252;hnhammer, K., Herbstritt, B., Gessler, A., & Weiler, M. (2016b). A method for in situ monitoring of the isotope composition of tree xylem water using laser spectroscopy. Plant, cell & environment, 39(9), 2055-2063.&#160;Jarvis, N. J. (1989). A simple empirical model of root water uptake. Journal of Hydrology, 107(1-4), 57-72.&#160;

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Ecohydrological travel times derived from in situ stable water isotope measurements in trees during a semi–controlled pot experiment

10.5194/hess-2020-674 ◽

2021 ◽

Author(s):

David Mennekes ◽

Michael Rinderer ◽

Stefan Seeger ◽

Natalie Orlowski

Keyword(s):

Water Uptake ◽

Sap Flow ◽

Measurement Techniques ◽

Quercus Suber ◽

In Situ Measurements ◽

Alnus Incana ◽

Travel Times ◽

Stem Height ◽

Isotope Measurements

Abstract. Recent advances in in situ measurement techniques for stable water isotopes offer new opportunities to improve the understanding of tree water uptake processes and ecohydrological travel times. In our semi–controlled experiment with 20–year–old trees of three different species (Pinus pinea, Alnus incana and Quercus suber) placed in large pots, we applied in situ probes for stable water isotope measurements to monitor the isotopic signatures of soil water and tree xylem before and after two deuterium labelled irrigations. Additional destructive sampling of soil and plant material complemented the in situ measurements and allowed for a comparison between destructive (cryogenic vacuum extraction and direct water vapour equilibration) and in situ isotope measurements. For the first labelling pulse, the tracer based travel time at a stem height of 15 cm was 0.7 days for all three tree species but at 150 cm height tracer based travel times ranged between 2.4 (for Alnus incana) and 3.3 days (for Quercus suber). The tracer based travel time from the root zone to 15 cm stem height was similar to the sap flow based travel times (i. e., for all trees 0.7 days). However, sap flow based travel times were 1.3 days (for Alnus incana) longer than tracer based travel times at 150 cm stem height. In terms of different between tree species, we found similar tracer movement in Pinus pinea and Alnus incanca while in Quercus suber tracer travel times were longer which is likely due to lower water uptake rates of Quercus suber. The comparison of destructive and in situ isotope measurement techniques suggests notable differences in the sampled water pools. In situ measurements of soil and xylem water were much more consistent between the three tree pots (on average standard deviations were by 8.4 ‰ smaller for δ2H and by 1.6 ‰ for δ18O for the in situ measurements) but also among the measurements from the same tree pot in comparison to the destructive methods (on average standard deviations were by 7.8 ‰ and 1.6 ‰ smaller for δ2H and δ18O, respectively). Our study demonstrates the potential of semi-controlled large scale pot experiments and high-frequent in situ isotope measurements for monitoring tree water uptake and ecohydrological travel times. It also shows that differences in sampling techniques or sensor types need to be considered, when comparing results of different studies and within one study using different methods.

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Monitoring tree species-specific water uptake strategies via continuous in-situ stable water isotope measurements

10.5194/egusphere-egu2020-16786 ◽

2020 ◽

Cited By ~ 1

Author(s):

Natalie Orlowski ◽

Stefan Seeger ◽

David Mennekes ◽

Hugo de Boer ◽

Markus Weiler ◽

...

Keyword(s):

Water Uptake ◽

Temporal Resolution ◽

Tree Species ◽

Isotopic Signature ◽

Plant Water ◽

Destructive Sampling ◽

Species Specific ◽

Isotope Measurements ◽

Water Isotope

Water isotope tracing techniques in combination with laser-based isotopic analyses have advanced our understanding of plant water uptake patterns providing opportunities to carry out observational studies at high spatio-temporal resolution. Studying these highly dynamic processes at the interface between soils and trees can be challenging under natural field conditions, as available water resources are difficult to control. On the other hand, the results of small pot experiments in the greenhouse using tree seedlings are often difficult to transfer to mature trees. Here, we setup a controlled outdoor large pot experiment with three different, 4-6 meter high and 20 year old trees: Pinus pinea, Alnus spaethii and Quercus suber. We took advantage of stable water isotope techniques by tracing plant water uptake from the root zone through the xylem via isotopically labelled irrigation water. We combined ecohydrological observations of sapflow, photosynthesis, soil moisture and temperature and soil matrix potential with high resolution measurements of water stable isotopes in soils and trees to understand how soil water is used by different tree species. We monitored the isotopic composition of soil and xylem water in high temporal resolution with in-situ isotope probes installed at different depths in the soil and different heights in the tree stem. We further compared the water isotopic composition of our in-situ monitoring setup with destructive sampling methods for soil and plant water (vapour equilibration method and cryogenic extraction).Our results from the continuous monitoring showed a distinct difference in the xylem sap isotopic signature between Quercus on the one hand and Alnus and Pinus on the other hand. This is likely due to different water use strategies of these tree species. The tree xylem isotopic signature of Alnus and Pinus responded to the isotopic label within one day and six days at 15 cm and 150 cm stem height, respectively. The peak isotopic signature in the tree xylem due to the label application was similar to the isotopic signature of the soil in 30 cm (for Alnus) and 15&#160;cm (for Pinus). Quercus showed a delayed and much slower increase in the xylem isotopic signature in response to the label and the highest values were significantly lower than the corresponding soil isotopic signatures. Our methodological comparison showed that the isotopic signature of the destructive samples (from both methods) had a larger spread and this spread tended to become larger with subsequent labeling. Destructive soil samples showed a wider isotopic variation than destructive xylem samples. The in-situ isotope measurements in comparison showed a relative constant small to medium spread for soil and xylem isotopic measurements. Our in-situ isotope probes therefore seem to be a potential alternative or supplement to destructive sampling offering much higher temporal resolution. The continuation of the labeling experiments in 2020 will allow us to further study tree-species specific water uptake strategies, which will become important under future climatic conditions in terms of development of adaptation strategies for sustainable forest management.

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Xylem water in riparian Willow trees (Salix alba) reveals shallow sources of root water uptake by in situ monitoring of stable water isotopes

10.5194/hess-2021-456 ◽

2021 ◽

Author(s):

Jessica Landgraf ◽

Dörthe Tetzlaff ◽

Maren Dubbert ◽

David Dubbert ◽

Aaron Smith ◽

...

Keyword(s):

Isotopic Composition ◽

Soil Water ◽

Water Uptake ◽

Sap Flow ◽

Root Water Uptake ◽

In Situ Monitoring ◽

Water Isotopes ◽

Stable Water Isotopes ◽

Salix Alba

Abstract. Root water uptake is an important critical zone process, as plants can tap various water sources and transpire these back into the atmosphere. However, knowledge about the spatial and temporal dynamics of root water uptake and associated water sources at both high temporal resolution (e.g. daily) and over longer time periods (e.g. seasonal) is still limited. We used cavity ring-down spectroscopy (CRDS) for continuous in situ monitoring of stable water isotopes in soil and xylem water for two riparian willow (Salix alba) trees over the growing season (May to October) of 2020. This was complemented by isotopic sampling of local precipitation, groundwater and stream water in order to help constrain the potential sources of root water uptake. A local flux tower, together with sap flow monitoring, soil moisture measurements and dendrometry were also used to provide the hydroclimatic and ecohydrological contexts for in situ isotope monitoring. In addition, bulk samples of soil water and xylem water were collected to corroborate the continuous in situ data. The monitoring period was characterised by frequent inputs of precipitation, interspersed by warm dry periods which resulted in variable moisture storage in the upper 20 cm of the soil profile and dynamic isotope signatures. This variability was greatly damped in 40 cm and the isotopic composition of the sub-soil and groundwater was relatively stable. The isotopic composition and dynamics of xylem water was very similar to that of the upper soil and analysis using a Bayesian mixing model inferred that overall ~90 % of root water uptake was derived from the upper soil profile. Sap flow and dendrometry data indicated that soil water availability did not seriously limit transpiration during the study period, though there was a suggestion that deeper (> 40 cm) soil water might provide a higher proportion of root water uptake (~30 %) in a drier period in the late summer. The study demonstrates the utility of prolonged real time monitoring of natural stable isotope abundance in soil-vegetation systems, which has great potential for further understanding of ecohydrological partitioning under changing hydroclimatic conditions.

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Analysis of Soil Water Response to Grass Transpiration

Soil and Water Research ◽

10.17221/6510-swr ◽

2013 ◽

Vol 1 (No. 3) ◽

pp. 85-98

Author(s):

Dohnal Michal ◽

Dušek Jaromír ◽

Vogel Tomáš ◽

Herza Jiří

Keyword(s):

Soil Water ◽

Water Uptake ◽

Preferential Flow ◽

Water Movement ◽

Control Volume ◽

Water Pressure ◽

Lower Boundary ◽

Root Water Uptake ◽

Water Dynamics ◽

Soil Water Dynamics

This paper focuses on numerical modelling of soil water movement in response to the root water uptake that is driven by transpiration. The flow of water in a lysimeter, installed at a grass covered hillslope site in a small headwater catchment, is analysed by means of numerical simulation. The lysimeter system provides a well defined control volume with boundary fluxes measured and soil water pressure continuously monitored. The evapotranspiration intensity is estimated by the Penman-Monteith method and compared with the measured lysimeter soil water loss and the simulated root water uptake. Variably saturated flow of water in the lysimeter is simulated using one-dimensional dual-permeability model based on the numerical solution of the Richards’ equation. The availability of water for the root water uptake is determined by the evaluation of the plant water stress function, integrated in the soil water flow model. Different lower boundary conditions are tested to compare the soil water dynamics inside and outside the lysimeter. Special attention is paid to the possible influence of the preferential flow effects on the lysimeter soil water balance. The adopted modelling approach provides a useful and flexible framework for numerical analysis of soil water dynamics in response to the plant transpiration.

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Modelling the Impact on Root Water Uptake and Solute Return Flow of Different Drip Irrigation Regimes with Brackish Water

Water ◽

10.3390/w11030425 ◽

2019 ◽

Vol 11 (3) ◽

pp. 425 ◽

Cited By ~ 3

Author(s):

Fairouz Slama ◽

Nessrine Zemni ◽

Fethi Bouksila ◽

Roberto De Mascellis ◽

Rachida Bouhlila

Keyword(s):

Water Content ◽

Soil Water ◽

Soil Water Content ◽

Water Uptake ◽

Brackish Water ◽

Deficit Irrigation ◽

Root Zone ◽

Root Water Uptake ◽

Return Flows ◽

Semi Arid

Water scarcity and quality degradation represent real threats to economic, social, and environmental development of arid and semi-arid regions. Drip irrigation associated to Deficit Irrigation (DI) has been investigated as a water saving technique. Yet its environmental impacts on soil and groundwater need to be gone into in depth especially when using brackish irrigation water. Soil water content and salinity were monitored in a fully drip irrigated potato plot with brackish water (4.45 dSm−1) in semi-arid Tunisia. The HYDRUS-1D model was used to investigate the effects of different irrigation regimes (deficit irrigation (T1R, 70% ETc), full irrigation (T2R, 100% ETc), and farmer’s schedule (T3R, 237% ETc) on root water uptake, root zone salinity, and solute return flows to groundwater. The simulated values of soil water content (θ) and electrical conductivity of soil solution (ECsw) were in good agreement with the observation values, as indicated by mean RMSE values (≤0.008 m3·m−3, and ≤0.28 dSm−1 for soil water content and ECsw respectively). The results of the different simulation treatments showed that relative yield accounted for 54%, 70%, and 85.5% of the potential maximal value when both water and solute stress were considered for deficit, full. and farmer’s irrigation, respectively. Root zone salinity was the lowest and root water uptake was the same with and without solute stress for the treatment corresponding to the farmer’s irrigation schedule (273% ETc). Solute return flows reaching the groundwater were the highest for T3R after two subsequent rainfall seasons. Beyond the water efficiency of DI with brackish water, long term studies need to focus on its impact on soil and groundwater salinization risks under changing climate conditions.

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SIMULATING SOIL WATER FLOW WITH ROOT-WATER-UPTAKE APPLYING AN INVERSE METHOD

Soil Science ◽

10.1097/01.ss.0000112018.97541.85 ◽

2004 ◽

Vol 169 (1) ◽

pp. 13-24 ◽

Cited By ~ 13

Author(s):

Qiang Zuo ◽

Lei Meng ◽

Renduo Zhang

Keyword(s):

Soil Water ◽

Water Flow ◽

Water Uptake ◽

Inverse Method ◽

Root Water Uptake ◽

Soil Water Flow

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Towards the consideration of soil-root resistances in root water uptake models with macroscopic representations of hydraulic root architecture

10.5194/egusphere-egu21-8151 ◽

2021 ◽

Author(s):

Jan Vanderborght ◽

Valentin Couvreur ◽

Felicien Meunier ◽

Andrea Schnepf ◽

Harry Vereecken ◽

...

Keyword(s):

Root System ◽

Soil Water ◽

Water Uptake ◽

Root Distribution ◽

Root Architecture ◽

Soil Layer ◽

Root Water Uptake ◽

Hydraulic Architecture ◽

Root Segments ◽

Soil Volume

Plant water uptake from soil is an important component of terrestrial water cycle with strong links to the carbon cycle and the land surface energy budget. To simulate the relation between soil water content, root distribution, and root water uptake, models should represent the hydraulics of the soil-root system and describe the flow from the soil towards root segments and within the 3D root system architecture according to hydraulic principles. We have recently demonstrated how macroscopic relations that describe the lumped water uptake by all root segments in a certain soil volume, e.g. in a thin horizontal soil layer in which soil water potentials are uniform, can be derived from the hydraulic properties of the 3D root architecture. The flow equations within the root system can be scaled up exactly and the total root water uptake from a soil volume depends on only two macroscopic characteristics of the root system: the root system conductance, Krs, and the uptake distribution from the soil when soil water potentials in the soil are uniform, SUF. When a simple root hydraulic architecture was assumed, these two characteristics were sufficient to describe root water uptake from profiles with a non-uniform water distribution. This simplification gave accurate results when root characteristics were calculated directly from the root hydraulic architecture. In a next step, we investigate how the resistance to flow in the soil surrounding the root can be considered in a macroscopic root water uptake model. We specifically investigate whether the macroscopic representation of the flow in the root architecture, which predicts an effective xylem water potential at a certain soil depth, can be coupled with a model that describes the transfer from the soil to the root using a simplified representation of the root distribution in a certain soil layer, i.e. assuming a uniform root distribution.

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