EGU2020-18071
https://doi.org/10.5194/egusphere-egu2020-18071
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Disentangling temporal and population variability in plant root water uptake from stable isotopic analysis: a labeling study

Valentin Couvreur1, Youri Rothfuss2, Félicien Meunier3,4, Thierry Bariac5, Philippe Biron5, Jean-Louis Durand6, and Mathieu Javaux2,7
Valentin Couvreur et al.
  • 1University of Louvain, Earth and Life Institute, Agronomy, Louvain-la-Neuve, Belgium (valentin.couvreur@uclouvain.be)
  • 2Institute of Bio- and Geosciences, IBG-3 Agrosphere, Forschungszentrum Jülich GmbH, Jülich, 52425, Germany
  • 3Ghent University, Department of Applied Ecology and Environmental Biology, CaveLab, Ghent, Belgium
  • 4Boston University, Department of Earth and Environment, Ecological Forecasting lab, Boston, MA, USA
  • 5Institute of Ecology and Environmental Sciences (IEES) – Paris, UMR 7618, CNRS-Sorbonne Université, Campus AgroParisTech, Thiverval-Grignon, 78850, France
  • 6UR P3F (INRA), Lusignan, 86600, France
  • 7University of Louvain, Earth and Life Institute, Environment, Louvain-la-Neuve, Belgium

Labeling techniques have been widely applied in the literature to infer profiles of plant relative root water uptake (RWU). By enhancing the rather flat water isotopic composition gradient in soil with labeled water, relative RWU values from a set of soil water “sources” can be determined from inversion of isotopic data with greater confidence. This is usually done in the isotopic community through Bayesian multi-source mixing models. These models are not demanding in terms of data (only isotopic data is required) but do not incorporate knowledge water transport processes. Combined observations of water status and flow (e.g., soil water matric potential and transpiration rate) and soil-root hydrodynamics models allow mining deeper into isotopic data, and provide novel insights into the spatiotemporal dynamics of water transport across plants.

A one-dimensional and isotope-enabled soil-root physically-based model was used to simulate both water and isotopic measurements recorded during a 34-hour long intensive labeling experiment where a population of tall-fescue (Festuca arundinacae) was grown in a macro-rhizotron (0.2 m2 surface area, 1.6 m depth). Above-ground data included tiller and leaf water oxygen isotopic compositions (δtiller and δleaf) as well as leaf water potential (ψleaf) and transpiration rate. As for below-ground data, profiles of root length density (RLD), soil water content and isotopic composition were destructively sub-hourly sampled. A first analysis of the results showed a striking decorrelation in temporal dynamics of water status and isotopic information.

There was no scenario in which the soil-root model could simulate both ψleaf and δtiller time series well. While the model-to-data fit for ψleaf was satisfying (R2=0.67), none of the tested root system groups of varying rooting depths could reproduce the measured temporal fluctuations of δtiller (R2=0.00). The model however showed the great sensitivity of δtiller to the population average rooting depth at the labeling point, thereby suggested spatial heterogeneity as the explanation for the observed temporal dynamics.

For comparison, one Bayesian mixing model was used and could successfully reproduce the δtiller high temporal dynamics induced by the labeling of deep soil water. If it succeeded in simulating RWU profiles, it was obviously at the expense of physical consideration: the strong variations in δtiller were translated into strong changes of RWU profile, which appeared not to be driven by environmental factors such as ψleaf and transpiration rate.

This study highlights the need for a holistic view, i.e., complement isotopic measurements with data on water status and calls for the use of physically-based soil-root model, especially in the context of labeling experiments.

How to cite: Couvreur, V., Rothfuss, Y., Meunier, F., Bariac, T., Biron, P., Durand, J.-L., and Javaux, M.: Disentangling temporal and population variability in plant root water uptake from stable isotopic analysis: a labeling study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18071, https://doi.org/10.5194/egusphere-egu2020-18071, 2020

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Display material version 1 – uploaded on 04 May 2020
  • CC1: Comment on EGU2020-18071, Maurizio Mencuccini, 06 May 2020

    dear Valentin,

    an excellent presentation and thanks for the link to the HESS manuscript in discussion. I wondered about the strong intercept shifts in the T-Psi plots between day and night. They seem to suggest substantial differences in the 'perceived' soil Psi at T=0. Is it likely to be a soil-root interface shift between night and daytime values? Is it possible that some of your optimised parameters change between daytime and nighttime?
    cheers
    Maurizio