Soil impact on plant hydraulics revealed by leaf rehydration kinetics

Abstract Background and Aims The hydraulic conductance of the soil is expected to become limiting for plant transpiration in drying soils. Specifically, coarse textured soils are expected to limit transpiration at less negative soil water potential (Ψ soil ). Yet, there is still limited experimental evidence on Ψ soil and relative transpiration rate at which the decline in soil conductance impacts plant water status and the whole soil to plant hydraulic conductance. This gap is related to the lack of accurate and temporally resolved measurements of soil and plant water potential and hydraulic conductance. Methods We combine rehydration techniques and water potential time-series measurements in wheat plants in two contrasting soil textures to measure the relative importance of soil and plant hydraulic conductance on stem water potential and transpiration rate. Results We found that during imposed water stress, a 50% reduction in transpiration rate was concomitant with the soil hydraulic conductance (K soil ) falling below the plant hydraulic conductance (K plant ): K soil declined to 18–56% of K plant in loam and to 7–39% in sand. Conclusions The relative importance of soil and plant hydraulics was texture-specific, with coarse-textured soils imposing greater resistance on soil to leaf water flow at less negative Ψ soil than fine-textured soils. Upon rewetting, the soil–plant hydraulic conductance rapidly reached values it had before the plant was exposed to drying. These results highlight the soil-texture dependency of soil hydraulic properties on plant response to soil drying. The high temporal resolution and non-invasive experimental method is capable to resolve the effect of declining soil hydraulic conductance on the overall soil–plant conductance. Highlight Leaf rehydration kinetics show that soil, not plant, limits water transport during drought—especially in coarse soils where hydraulic conductance drops at less negative water potential.