Effect of soil texture on root water uptake

Mhimdi, Imen [UCL] Dagmar van Dusschoten Javaux, Mathieu [UCL]

Understanding how root water uptake (RWU) depends on soil properties is a key to estimate plant transpiration dynamics and its response to climate. Despite the fact that soil texture plays an important role in determining plant water availability and mechanical resistance, texture and RWU have not often been considered simultaneously in literature. Recently, a novel method was developed by (van Dusschoten et al, 2020), the SWaP (Soil Water Profiler), in which soil water content and its depletion could be monitored during a modulated light regime in order to derive the RWU profile. The scope of our work is to investigate with the SWaP how soil texture impacts RWU dynamics. We hypothesize that the soil texture will impact the distribution of the rhizosphere resistance in the rhizosphere and thereby its RWU. Eight faba bean (Vicia Faba) plants were grown in 45cm PVC pots, two soil textures (Loamy and Sandy) with different dry density were used. The plants were subjected to progressive water deficits, and were measured continuously with the SWaP, while applying light modulations during daytime to measure instantaneous 1D water content and derived root water uptake profiles. In combination with the SWaP, several MRI measurements were performed combined with image analysis, in order to determine the local root length distribution and its relation to RWU. For loamy soil, MRI measurements showed a structured spiral shape, an extensive and deeper root system with higher root diameter. Roots were less smooth, tortuous and with denser lateral roots in sandy soil. In both textures, root water uptake decreased with depth, which can be explained by the less abundant roots in lower soil layers and a higher resistance for the deeper roots (Müllers et al, 2023). Root water uptake profiles and total water uptake dynamics were different, between soil types, which could partially be attributed to differences in root distribution.