Co-regulation of water use and canopy temperature in desert trees

Plants employ a range of water-use strategies to withstand limitations in water supply and increases in atmospheric demand. At the same time, water-use strategies alter canopy energy balance, leading to changes in canopy temperature that can impact photosynthesis, creating distinct tradeoffs between water and temperature regulation. However, the extent of these tradeoffs is a key uncertainty in understanding plant responses to hydroclimatic stress. Here, we use a unique dataset of near-surface remotely sensed retrievals of canopy conductance, transpiration, and temperature to assess how desert trees co-regulate their water status and temperature. We leverage a moisture gradient and seasonality in temperature to evaluate species-specific plant responses to both isolated (cool, dry and hot, wet) and combined (hot, dry) water and temperature stress and compare them to reference (cool, wet) conditions. We find that species exhibit different water-use strategies in response to supply- and demand-driven water stress, but exhibit similar responses to thermal stress. Under most conditions, plants face tradeoffs between hydraulic function and avoiding thermal stress. However, when both supply and demand are high, water and canopy temperature regulation can become decoupled. Altogether, our findings reveal two unexpected plant behaviors that may be particularly vulnerable to climate change. • Regulation of transpiration in response to water stress differs between species. • Regulation of canopy temperature is similar between species. • When supply and demand are high, water-use and temperature regulation are decoupled.