Understanding the drivers of hydraulic redistribution under salt stress

Hydraulic redistribution (HR), the passive movement of water through plant root systems from wet to dry soil layers, plays a critical role in maintaining plant water status and nutrient uptake in water-limited environments. While HR is well-documented under drought, its dynamics become significantly more complex in saline conditions where total soil water potential is driven by both matric and osmotic components.

In this study, we employed a split-root experimental design using young avocado trees to isolate and quantify HR. The root system of each tree was divided between two pots: a "wet pot" maintained at field capacity and a "drying pot" where irrigation was withheld. We utilized high-precision weighing lysimeters to monitor nocturnal weight changes in the drying pot, alongside soil moisture sensors and isotopic water labelling to track water movement.

Our preliminary results confirm the occurrence of HR in young avocado trees under non-saline control conditions. The phenomenon was clearly identified in two out of three trees monitored during the initial experimental phase, as evidenced by nocturnal increases in soil water content and corresponding weight changes in the drying pots. These findings provide a foundational baseline for the next phase of the research, which aims to evaluate how increasing levels of salt stress (NaCl) in the wet pot influence the osmotic gradients and root hydraulic conductivity that drive HR. By comparing control and saline treatments, we seek to determine whether salinity-induced changes in total water potential suppress or shift the patterns of hydraulic redistribution.