Sensitivity of physiological traits to different short-term drought events and subsequent recovery at the sapling stage in European white elm (Ulmus laevis Pall.)

Abstract

There is an urgent need to better understand the processes underlying trees resistance and resilience to drought as a prerequisite for adapting to climate change. In this study, the effect of different short-term drought events on the physiology of European white elm saplings, as well as the rates at which their physiological traits recover after drought were identified. Elm saplings responded sensitively to drought stress: leaf water potential, net photosynthesis and stomatal conductance were the most sensitive traits. The normalized difference vegetation index and leaf water content responded only to severe drought stress conditions. Drought triggered the conversion of soluble carbohydrates to starch in leaves but not in roots. Root function was severely damaged by drought as indicated by increased root electrolyte leakage. Tree survival and the recovery rate were significantly better under two shorter drought periods compared to one longer drought. For this reason, the precipitation pattern in models evaluating tree survival under climatic change has to be taken into account. The differences in the studied traits between surviving and dying saplings increased as drought progressed and leaf water content together with leaf reflectance indexes were identified as the best indicators for evaluating tree mortality risk. These findings are very important, as they show that these specific traits can be used to identify trees susceptible to drought in the field as they can be sensed remotely.