Book/Dissertation / PhD Thesis

FZJ-2015-04837

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png The role of soil heterogeneity on field scale evapotranspiration: 3D integrative modellingand upscaling of root water uptake

Huber, K. (Corresponding author)FZJ*

2015
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 978-3-95806-057-9

Please use a persistent id in citations: http://hdl.handle.net/2128/9008  urn:nbn:de:0001-2015071401

Abstract: Background and Motivation: Hydrological models mainly rely on empirical functions to describe rootwater uptake. However, in case of water limitation due to either scarce or heterogeneously distributedsoil water, plants have developed strategies to adapt. One short-term strategy is the regulation ofstomatal aperture either by plant hydraulics or phyto-hormones. The latter are thought to act as a kindof sensor for dry soil. It can be assumed that hormones are produced locally in single root segments asfunction of low root water potentials. After being transported with the xylem stream they becomeeffective in stomatal closure. Long-term adaptation strategies are mostly related to changes in carbonallocation within the plant and result in growth adaptations. Both strategies often remain insufficientlyrepresented in hydrological models.Methods: R-SWMS, a mechanistic soil and root water flow model that operates at the scale of a singleroot system was used to conduct a variety of virtual experiments. The model simulates threedimensional water flow through the soil, to, and within the roots. It was extended by a module toaccount for additional hormonal signalling, subsequently testing its influence in virtual split-rootexperiments. In a next step, direct mathematical relationships that link effective soil water potentialand transpiration were derived. Considering the long-term adaptation strategies, the numerical modelwas modified to incorporate measured dynamic root architectures.Results: Measured hormone concentrations in the leaves and some phenomena, like e.g. oscillations instomatal aperture, were reproduced by the model. The direct relationships between soil water potentialand transpiration showed that the stomatal behaviour depends on the underlying control and itsparameterization. Experimental data, visualizing root systems over a 30 day growth period, wereobtained from UFZ Halle, Germany, by CT scans. This dataset showed that plants grown underpermanently limited water supply were considerably smaller with correspondingly less total wateruptake compared to plants with initially unrestricted water resources. In combination with thenumerical model, the flow dynamics in the soil-root system were resolved. The predicted location ofroot water uptake was found to be different from the measured zone of water depletion.Conclusion: The implementation of bio-physical relationships into a mechanistic root soil modelresulted in a powerful tool to identify key processes for plant water use in agricultural environments.This work provided new direct relationships between the effective soil water potential andtranspiration rate in case stomata are controlled by hormones. In combination with an experimentaldataset it gave new insights into water pathways within the soil-plant continuum.

Note: Dissertation, Univ. Bonn, 2014

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Contributing Institute(s):

1. Agrosphäre (IBG-3)

Research Program(s):

1. 255 - Terrestrial Systems: From Observation to Prediction (POF3-255) (POF3-255)

Appears in the scientific report 2015

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Database coverage:

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