Deep‐water uptake under drought improved due to locally increased root conductivity in maize, but not in faba bean

Abstract

Moderate soil drying can cause a strong decrease in the soil‐root system conductance. The resulting impact on root water uptake depends on the spatial distribution of the altered conductance relatively to remaining soil water resources, which is largely unknown. Here, we analyzed the vertical distribution of conductance across root systems using a novel, noninvasive sensor technology on pot‐grown faba bean and maize plants. Withholding water for 4 days strongly enhanced the vertical gradient in soil water potential. Therefore, roots in upper and deeper soil layers were affected differently: In drier, upper layers, root conductance decreased by 66%–72%, causing an amplification of the drop in leaf water potential. In wetter, deeper layers, root conductance increased in maize but not in faba bean. The consequently facilitated deep‐water uptake in maize contributed up to 21% of total water uptake at the end of the measurement. Analysis of root length distributions with MRI indicated that the locally increased conductance was mainly caused by an increased intrinsic conductivity and not by additional root growth. Our findings show that plants can partly compensate for a reduced root conductance in upper, drier soil layers by locally increasing root conductivity in wetter layers, thereby improving deep‐water uptake.

Root Phenotyping and Root Water Uptake Calculation Using Soil Water Contents Measured in a Winter Wheat Field

“…It has been used to estimate gross primary productivity of ecosystems where experimental measurements are infeasible (Beer et al, 2007;Cheng et al, 2017). While root water uptake has been studied for centuries, some issues, such as how plants adjust their water uptake from different soil layers in response to environmental change as well as the underlying mechanisms, remain elusive (Bonan et al, 2014;Chen et al, 2020;Gat, 1996;Penman and Keen, 1948;Williams et al, 2004), and processes are stilling be made (Müllers et al, 2022;Müllers et al, 2023).…”

“…Spatiotemporal change in soil water content is the footprint of root water uptake and it can hence be used to interpret root traits and root water uptake (Vandoorne et al, 2012). The easiest way is soil-drying method where root water uptake from a soil layer is assumed to be the difference in soil water contents measured at two time points (Dardanelli et al, 1997;Garre et al, 2011;Müllers et al, 2023;Nelson et al, 2006). This method does not need soil parameters and works well when soil is relatively dry in that soil water change is predominantly induced by root water uptake and water redistribution induced by gravity and matric potential gradient is negligible.…”