Characterization of photosynthesis and transpiration in two rubber tree clones exposed to thermal stress

Temperature is one of the most important factors influencing physiological responses of rubber trees, so much so that it is a limiting factor in the expansion of rubber tree plantations in Brazil. The aim of this research was to investigate the influence of thermal stress, characterized by different thermal amplitudes, on photosynthesis, stomatal conductance, transpiration and leaf temperature. Seedlings of two rubber tree clones, RRIM 600 and CDC 312, were exposed to three different environments which were characterized by the following daily temperature ranges: 25–30 °C (E1); 25–42 °C (E2) and 10–42 °C (E3). Gas exchange and leaf temperature measurements were performed during the experimental period. The results show that gas exchange was affected by higher thermal amplitudes (E2 and E3). Photosynthesis, stomatal conductance and transpiration were lower in E2 and E3 environments, being more pronounced in E3. It was also observed that, due to the higher thermal amplitude in E2 and E3, there was an increase in intercellular CO2 concentration. Reduction in transpiration rates culminated in an increase in leaf temperature in E2 and E3, being more pronounced in the CDC 312 clone than in RRIM 600.