Simultaneous in situ monitoring of belowground, stem and relative stomatal hydraulic conductances of grapevine demonstrates a soil-texture specific transpiration control

Abstract Background and aims Assessing the interrelationships between belowground, stem and stomatal hydraulics, under various edaphic conditions, is essential to enhance understanding of how grapevine (Vitis vinifera) responds to drought. This work aimed to understand the roles of belowground and stem hydraulics of the soil-grapevine system on the transpiration control of in situ grapevine during drought.Methods We simultaneously monitored soil water potential, stem water potential, leaf water potential and actual transpiration and investigated how belowground, stem and relative stomatal hydraulic conductances of in situ grapevines evolve and coordinate during a drought event on different soil types.Results Stomatal response was triggered by a decrease of belowground hydraulic conductance, but not by xylem cavitation in the stem. Stomata started to close at less negative soil water potential in sand than in loam and stomatal downregulation is sharper in coarse-textured than in fine-textured soils. Despite these contrasted responses to soil water potential, we observed, for the first time on in situ perennial plants such as grapevine, that the onset of stomatal closure was at the same belowground hydraulic conductance for each subplot, independently of the soil texture.Conclusion These findings prove that in situ grapevines coordinate short-term hydraulic mechanisms (e.g. stomatal regulation) and longer-term growth (e.g. root:shoot ratio). These belowground and aboveground adjustments should therefore be soil-texture specific.