From Root to Shoot: Understanding Plant Hydraulic Regulation Across Different Soil Moistures

Efficient coordination between aboveground (Kab) and belowground (Kbe) hydraulic conductance is crucial for plants to meet evaporative demands in diverse environmental conditions. Despite significant advances in understanding hydraulic traits, the interplay between Kab and Kbe under varying soil moisture levels remains insufficiently explored. This study investigates how maize (Zea mays L.) regulates hydraulic conductance during development in response to optimal (OWC, 25–30% volumetric water content) and water-stressed (SWC, 10–15%) soil conditions.

A controlled greenhouse experiment measured Kab and Kbe at 14, 26, 35, and 55 days after sowing. Kbe was quantified using a pressure chamber, while Kab components were derived from transpiration rates, leaf water potential, and environmental parameters. Results showed that Kbe exceeded Kab by two orders of magnitude and increased consistently with plant age, reflecting root system expansion. Plants under OWC exhibited significantly higher Kbe and Kab compared to SWC, where growth and hydraulic conductance plateaued earlier. Coordination between Kab and Kbe was linear at early stages but diverged as Kbe plateaued under SWC, while Kab continued to increase.

The trajectory of Kab and Kbe coordination was consistent across both treatments, but OWC plants explored a higher hydraulic capacity, indicating superior water uptake and transport. In contrast, SWC plants maintained the same coordination trajectory but operated at a reduced magnitude, reflecting an adaptive response to conserve water. These findings underscore the critical role of water availability in shaping plant hydraulic traits and highlight strategies for improving water use efficiency and resilience in agricultural systems under drought stress.