Shaping rhizosphere properties enables better root water uptake performance in contrasting soil conditions

Plants actively modify their rhizosphere by releasing carbon-rich exudates that alter the physical and hydraulic properties of the surrounding soil. High-molecular-weight compounds such as mucilage are known to enhance rhizosphere water retention and increase liquid-phase viscosity. However, it remains poorly understood whether maize strategically modulates mucilage exudation in response to contrasting soil textures and water availability. Soil hydraulic properties differ strongly between textures, particularly under drying conditions, where non-linear relationships between matric potential and hydraulic conductivity may constrain root water uptake. We hypothesized that maize enhances mucilage exudation in soils with reduced soil–root contact and low hydraulic conductivity in order to maintain water uptake.

We grew maize plants in rhizoboxes filled with two contrasting soil textures (sand and loam) under well-watered and water-limited conditions. Rhizosphere extension around newly emerged roots was quantified using neutron radiography. In a second experiment, soil water was labeled with deuterated water to quantify root water uptake dynamics using time-resolved neutron radiography combined with a diffusion–convection model.

Rhizosphere extension was significantly larger in sand than in loam, indicating an adaptive modification of rhizosphere properties in response to reduced soil–root hydraulic connectivity. This pattern is consistent with enhanced mucilage exudation, which increases soil–root contact and maintains liquid-phase continuity under hydraulically limiting conditions. For the first time, in situ water retention curves of the maize rhizosphere were quantified for both sandy and loamy soils. Root water uptake rates of individual roots were similar across soil textures and moisture regimes; however, individual roots in sandy soils contributed more strongly to total plant transpiration than those in loamy soils. Notably, single roots maintained water uptake under water-limited conditions, demonstrating the capacity of maize to sustain water acquisition even as soil moisture declined.

These results demonstrate a high degree of adaptive plasticity in maize, highlighting its ability to engineer rhizosphere hydraulic properties to optimize water uptake under contrasting soil textures and moisture regimes.