Implementing small scale processes at the soil-plant interface – the role of root architectures for calculating root water uptake profiles

C L Schneider,S Attinger,A Hildebrandt,J.-O Delfs

doi:10.5194/hess-14-279-2010

Abstract

Abstract. In this paper, we present a stand alone root water uptake model called aRoot, which calculates the sink term for any bulk soil water flow model taking into account water flow within and around a root network. The boundary conditions for the model are the atmospheric water demand and the bulk soil water content. The variable determining the plant regulation for water uptake is the soil water potential at the soil-root interface. In the current version, we present an implementation of aRoot coupled to a 3-D Richards model. The coupled model is applied to investigate the role of root architecture on the spatial distribution of root water uptake. For this, we modeled root water uptake for an ensemble (50 realizations) of root systems generated for the same species (one month old Sorghum). The investigation was divided into two Scenarios for aRoot, one with comparatively high (A) and one with low (B) root radial resistance. We compared the results of both aRoot Scenarios with root water uptake calculated using the traditional Feddes model. The vertical rooting density profiles of the generated root systems were similar. In contrast the vertical water uptake profiles differed considerably between individuals, and more so for Scenario B than A. Also, limitation of water uptake occurred at different bulk soil moisture for different modeled individuals, in particular for Scenario A. Moreover, the aRoot model simulations show a redistribution of water uptake from more densely to less densely rooted layers with time. This behavior is in agreement with observation, but was not reproduced by the Feddes model.

Highlights

The global water and carbon cycles are key issues in climate and global change research
The plotted points represent entities on the bulk scale where the root length density (RLD) was calculated by counting root segment lengths in each bulk soil grid cells and root water uptake (RWU) is the given sink term of the bulk soil water flow in Eq (1)
Our model currently runs with a 3-D Richards Model it is intended for later implementation in SVAT schemes and for testing hypotheses on optimal root behavior in different environments

Summary

Introduction

The global water and carbon cycles are key issues in climate and global change research. Within these complex systems, plants are the central interface between the atmosphere and hydrosphere. Transpiration plays a crucial role for the surface energy balance as well as for the water cycle. Hydrological as well as climate models will benefit from an improved understanding of the process of water flow through plants, in particular because they are sensitive to root water uptake parameters (Desborough, 1997; Zeng et al, 1998). Great uncertainty in modeling transpiration stems from lack of knowledge about how much water is available to plant roots (Lai and Katul, 2000; Feddes et al, 2001)

Results

Discussion

Conclusion