Preservation of Thermal Stability of Cell Membranes and Gas Exchange in High Temperature Acclimated Xylia xylocarpa Seedlings

Xylia xylocarpa seedlings were grown for two months at 20 °C and exposed daily to mid-day temperatures of 25 °C, 30 °C, 35 °C, and 40 °C for 6–8 hours. The seedlings were subjected to short-term temperature treatments ranging from 20 °C to 50 °C and their net photosynthesis, stomatal conductance and electrolyte leakage from leaves were studied. The optimum temperature for height growth of seedlings was 35 °C. However, plants acclimated to 40 °C mid-day treatment had higher rates of net photosynthesis when exposed to lower (20–30 °C) and higher (50 °C) air temperatures. At 20 °C, the 40 °C-acclimated plants maintained relatively high stomatal conductance. However, at 50 °C, seedlings acclimated to higher air temperatures maintained lower stomatal conductance and leaked less electrolytes from the leaves compared with the plants exposed to lower mid-day temperatures. The results suggest that photosynthetic acclimation to higher temperatures involves an increase in water use efficiency and preservation of thermal stability of the cell membranes.