Rhizosphere hydraulic regulation in maize: tailoring rhizosphere properties to varying soil textures and moistures

Aims: Motivated by recent studies highlighting the active role of plants in influencing the hydraulic properties of the rhizosphere through mucilage exudation, this study explored the effect of plant rhizosphere regulation on the emergent hydraulic properties of the rhizosphere under varying soil texture and moisture levels. Methods: Maize (Zea mays) plants were cultivated in sand and loam soils exposed to varying moisture levels. Neutron radiography was employed to quantify the profile of water content (θ_r) around lateral and crown roots. The θ_r were used to derive rhizosphere hydraulic indices such as rhizosphere extension (d_rh), water content at the root-soil interface (θ_rs), and water content in the rhizosphere (θ_rh). The latter two attributes were normalized by the respective bulk soil water contents (θ_rs^∗, θ_rh^∗). Results: Results showed a higher θ_rs^∗, θ_rh^∗ and d_rh in coarse-textured soil versus fine-textured soil. This indicates a more pronounced rhizosphere development in sand compared to loam, possibly via mucilage exudation to maintain better root-soil contact. In contrast, soil water content did not impact the rhizosphere properties of crown roots but impacted the rhizosphere properties of lateral roots. The derived rhizosphere water retention curves revealed a higher water-holding capacity of the rhizosphere in both soils compared to bulk soil. Conclusions: Our study underscores that soil-grown maize plants dynamically adjust the hydraulic properties of their rhizosphere in response to external factors, primarily aiming to optimize root-soil contact. That leads to a more pronounced rhizosphere in coarser textures, interacting with the soil moisture.