Effect of soil moisture hysteresis on root water uptake: 1D Model

Abstract

The coupled dynamics of soil moisture movement and plant root water uptake and determines the spatio-temporal distribution of soil water content (θs) and evapotranspiration in the vadose zone. The efficiency of root water uptake and soil moisture hysteresis are significantly correlated, according to the results, with different patterns showing up during wetting and drying cycles. The significance of taking into account hysteresis effects in accurately estimating plant water acquisition under different climatic conditions is highlighted by the non-linear relationship between soil moisture and root water uptake.Current modeling approaches to predict this dynamics involves coupling the transient Richards equation (soil moisture movement) with a steady state Darcy equation (root water movement) through a sink term that represents the flux of water exchanged between the soil and root systems. These one-dimensional (vertical) models are often coupled with above ground canopy models to make predictions of land-surface fluxes in the critical zone. Over the course of a (non-rainy) diurnal period the soil typically experiences a decline in water content during the day and an increase in water content at night due to capillary wicking from deeper layers, and hydraulic redistribution. Over a growing season, the vadose zone experiences several such wetting and drying hysteretic cycles.However, current models ignore the effect of soil moisture hysteresis. Additionally, the root water uptake formulations employed in current models do not account for variations in root axial hydraulic conductivity with root water potential. Here we develop a coupled root-soil model (vRoot) that includes the effect of soil moisture hysteresis and dynamically varying, root water potential dependent, root axial hydraulic conductivities. Our coupled model shows that the effect of hysteresis on root water uptake.The findings of this study emphasize the importance of taking soil moisture hysteresis into account when evaluating plant-water relationships and have implications for enhancing water management techniques in agriculture and ecosystem modeling.