Simultaneous in situ monitoring of belowground, trunk and relative canopy hydraulic conductance of grapevine demonstrates a soil texture-specific transpiration control

Assessing the interrelationships between belowground, trunk and canopy hydraulics, under various edaphic conditions, is essential to enhance understanding of how grapevine (Vitis vinifera) responds to drought. This work aimed to quantify and compare in situ belowground and trunk hydraulic conductance of the soil-grapevine system to evaluate their coordination with the transpiration control during drought. We simultaneously monitored soil water potential, trunk xylem water potential, canopy xylem water potential, actual transpiration and atmospheric demand to quantify the evolution of belowground, trunk and relative canopy hydraulic conductance. By comparing stomatal regulation at the canopy scale and soil-grapevine system conductance, we assessed their coordination. Transpiration control was triggered by a decrease of belowground hydraulic conductance, and not by xylem cavitation in the trunk. Although the relation between canopy conductance and soil water potential is soil texture specific, where stomata at the canopy scale started to close at less negative soil water potential in sand than in loam, the onset of stomatal closure at the canopy level was at equivalent belowground hydraulic conductance, independently of the soil texture. These findings prove that in situ grapevines coordinate short-term hydraulic mechanisms (e.g., regulation of canopy hydraulic conductance) and longer-term growth (e.g., root:shoot ratio). These belowground and aboveground adjustments are, therefore, soil-texture specific.