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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/hess-2020-180
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/hess-2020-180
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 04 May 2020

Submitted as: research article | 04 May 2020

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This preprint is currently under review for the journal HESS.

Comparison of root water uptake models in simulating CO2 and H2O fluxes and growth of wheat

Thuy Huu Nguyen1, Matthias Langensiepen1, Jan Vanderborght3, Hubert Hüging1, Cho Miltin Mboh1, and Frank Ewert1,2 Thuy Huu Nguyen et al.
  • 1University of Bonn, Institute of Crop Science and Resource Conservation (INRES), Katzenburgweg 5, 53115 Bonn, Germany
  • 2Leibniz Centre for Agricultural Landscape Research (ZALF), Institute of Landscape Systems Analysis, Eberswalder Strasse 84, 15374 Muencheberg, Germany
  • 3Agrosphere, Institute of Bio- and Geosciences (IBG-3), Forschungszentrum Jülich GmbH, 52428, Jülich, Germany

Abstract. Stomatal regulation and whole plant hydraulic signaling affect water fluxes and stress in plants. Land surface models and crop models use a coupled photosynthesis–stomatal conductance modelling approach and estimate the effect of soil water stress on stomatal conductance directly from soil water content or matrix potential without explicit representation of hydraulic signals between the soil and stomata. In order to explicitly represent stomatal regulation by soil water status as a function of the hydraulic signal and its relation to the whole plant hydraulic conductance, we coupled the crop model LINTULCC2 and the root growth model SLIMROOT with Couvreur's root water uptake model (RWU), and the HILLFLOW soil water balance model. Since plant hydraulic conductance depends on the plant development, this model coupling represents a two-way coupling between growth and plant hydraulics. To evaluate the advantage of considering plant hydraulic conductance and hydraulic signaling, we compared the performance of this newly coupled model with another commonly used approach that relates root water uptake and plant stress directly to the root zone water potential (HILLFLOW with Feddes' RWU model). Simulations were compared with gas flux measurements and crop growth data from a wheat crop grown under three water supply regimes (sheltered, rain-fed and irrigated) and two soil types (stony and silty) in Western Germany in 2016. The two models showed a relatively similar performance in simulation of dry matter, LAI, root growth, RWU, gross assimilation rate, and soil water content. The Feddes model predicts more stress and less growth in the silty soil than in the stony soil, which is opposite to the observed growth. The Couvreur model better represents the difference in growth between the two soils and the different treatments. The newly coupled model (LINTULCC2 – SLIMROOT – Couvreur – HILLFLOW) was also able to simulate the dynamics and magnitude of whole plant hydraulic conductance over the growing season. This demonstrates the importance of two-way feedbacks between growth and root water uptake for predicting the crop response to different soil water conditions in different soils. Our results suggest that a better representation of the effects of soil characteristics on root growth is needed for reliable estimations of root hydraulic conductance and gas fluxes, particularly in heterogeneous fields. The newly coupled soil–plant model marks a promissing approach but requires further testing for other scenarios regarding crop, soil, and climate.

Thuy Huu Nguyen et al.

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Short summary
The mechanistic Couvreur root water uptake (RWU) model that is based on plant hydraulics and links root system properties to RWU, water stress, and crop development can evaluate the impact of certain crop properties on crop performance in different environments and soils, while the Feddes RWU approach does not possess such flexibility. This study also shows the importance of modelling root development and how it responds to water deficiency to predict the impact of water stress on crop growth.
The mechanistic Couvreur root water uptake (RWU) model that is based on plant hydraulics and...
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