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 degrees C and exposed daily to mid-day temperatures of 25 degrees C, 30 degrees C, 35 degrees C, and 40 degrees C for 6-8 hours. The seedlings were subjected to short-term temperature treatments ranging from 20 degrees C to 50 degrees C and their net photosynthesis, stomatal conductance and electrolyte leakage from leaves were studied. The optimum temperature for height growth of seedlings was 35 degrees C. However, plants acclimated to 40 degrees C mid-day treatment had higher rates of net photosynthesis when exposed to lower (20-30 degrees C) and higher (50 degrees C) air temperatures. At 20 degrees C, the 40 degrees C-acclimated plants maintained relatively high stomatal conductance. However, at 50 degrees 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.