Soil Rather Than Xylem Vulnerability Controls Stomatal Response to Drought

The current trend towards linking stomata regulation to plant hydraulics emphasizes the role of xylem vulnerability. Using a soil–plant hydraulic model, we show that xylem vulnerability does not trigger stomatal closure in mediumwet to dry soils and we propose that soil hydraulic conductivity loss is the primary driver of stomatal closure. This finding has two key implications: transpiration response to drought cannot be derived from plant traits only and is related to soil–root hydraulics in a predictable way; roots and their interface with the soil, the rhizosphere, are key hydraulic regions that plants can alter to efficiently adapt to water limitations. We conclude that connecting below- and aboveground hydraulics is necessary to fully comprehend plant responses to drought