Long-term acclimation to different stress types: revealing tradeoffs between mesophyll and stomatal conductance

AbstractZiziphus spina-christi, a thermophilic tree, became more abundant in the Mediterranean, presumably due to increased winter temperatures. In order to predict the plant acclimation to future climate changes, we attempted to understand which factors underlie photosynthetic stress acclimation.Stress acclimation to three major long-term abiotic stresses (drought, salinity and temperature) was investigated by measuring growth, gas exchange, chlorophyll fluorescence and leaf structure. We developed a stress index that allowed to precisely define stress level, enabling a comparison between stress types. For each stress, photosynthesis-limiting factors were compared: stomatal conductance (gs), mesophyll conductance (gm) and maximum capacity for Rubisco carboxylation (Vcmax).Photosynthesis under all stresses was limited mostly bygsandgm(80-90%); whereas biochemistry (Vcmax) made a minor contribution (10-20%). The relative contribution ofgsandgmon photosynthetic limitation was influenced by stress type. During acclimation to drought or salinity, photosynthesis was limited by a decline ings, while intolerance to low temperatures was driven by decline ingm. Low mesophyll-imposed limitation was the best predictor of abiotic stress tolerance.The results demonstrate how warming climate benefits thermophilic species. Moreover, current work gives methodology for stress studies, and defines the main factors underlying the plant response to climate change.HighlightWe have compared the photosynthesis limitation resulting from long-term acclimation to three major a-biotic stresses (drought, salinity and temperature) to understand which limiting-factor are dominant under each type of stress.