H21B-06 Efficient representation of soil and root hydraulic properties in root water uptake models

Jan Vanderborght Couvreur, Valentin [UCL] Juan Baca-Cabrera Daniel Leitner Lobet, Guillaume [UCL] Javaux, Mathieu [UCL] Andrea Schnepf

Water uptake by plant roots is an important component of the soil water balance and of the land surface - atmosphere water exchange. Root water uptake depends on atmospheric demand and the water supply from the soil, which is controlled by both soil and root hydraulic properties. Mechanistic models that describe flow in the soil-root system and consider the hydraulic properties of roots and soil can be used to derive supply functions. Unfortunately, these models are often data intensive, which hinders their widespread use. Distributions of root system hydraulic conductivities that were derived from literature showed a large variation of conductivities for a given crop or plant species that was larger than the variation between species. Root system or plant age explained part of this variability. Uncertainty about root system hydraulic properties is hence an important source of uncertainty about soil water supply. Due to the non-linearity of soil hydraulic properties, mechanistic models are computationally expensive. Therefore, we developed functions that calculate the supply directly from soil water potentials and atmospheric demand. These functions are parameterized based on the plant and soil hydraulic properties and we derived approaches to calculate the parameters directly from these properties. We found that these functions show similarities with empirical functions that are used in soil water balance models but also show some differences. In contrast to commonly used empirical functions, soil properties have an important effect on the obtained water supply functions. Since these functions and their parameters couple soil and plant hydraulic properties with plant water status and atmospheric demand directly and efficiently, this opens new perspectives to reduce the uncertainty about root system hydraulic properties using models that couple plant and root growth and development with plant water status.