Limited plastic responses in safety traits support greater hydraulic risk under drier conditions

Understanding how plants adjust their hydraulic system to the environment is essential to predict how these organisms will respond to global change. Here we compiled a dataset and performed meta-analysis on 223 studies on plastic and evolutionary adjustments of hydraulic traits to air temperature, CO2 concentration, irradiance, soil nutrient and water availability. On average, species plastically increased embolism resistance and sapwood area per leaf area under drier conditions, with a decrease in stem-specific hydraulic conductivity and water potential at the turgor loss point, which are consistent with adaptive responses. However, the average increased embolism resistance was not sufficient to compensate the reduction in the minimum water potential, implying a lower safety margin from lethal hydraulic failure under drought. These results point towards a general critical increase in the risk of hydraulic failure in future drier environments. Plastic responses to increased soil nutrient content and irradiance did not always align with those to drought, highlighting the potential for changes in light and nutrient conditions to modify plant hydraulic responses to climate-change-driven droughts. Plants across many ecosystems are increasingly exposed to dryness stress. Using meta-analysis, the authors show that plants can adjust their hydraulic traits in response to drought and other global change factors, but not equally across traits and not enough to prevent lethal hydraulic failure.