Photosynthesis in longan and mango as influenced by high temperatures under high irradiance.
Yamada M., Fukumachi H., Hidaka T.
Author Affiliation: Okinawa Subtropical Station, Japan International Research Center for Agricultural Sciences, MAFF, Maezato, Ishigaki, Okinawa 907, Japan.
Journal of the Japanese Society for Horticultural Science 64 : 749-756
Abstract : Leaves of 2-year-old longan and mango seedlings were exposed to high irradiance (2000 µmol?m-2s-1) provided by metal halide lamps at 70±5% RH. Temperature was raised by increments of 3°C every 1.5 h, from 30 to 36°. Net assimilation rates decreased for both species as temperature increased, but the decline was greater in longans than in mangoes. As temperature increased, stomatal conductance decreased and intercellular CO2 concentration increased for both species, especially longans. A significant positive correlation was found in longan between stomatal conductance and net assimilation rate at 30 and 33°, but not at 36°. In mangoes, the correlation coefficient was significant at all 3 temperatures. Intercellular CO2 concentration and net assimilation rate were not closely related at 30 and 33°, but showed a strong negative correlation at 36° in both species. These results indicate that the decline in net assimilation rate was caused by non-stomatal limitations at high temperatures. In further experiments, the extent of decline in the chlorophyll fluorescence ratio (variable (Fv) to maximum fluorescence (Fm)) caused by high temperature treatment (up to 45°) in the dark was greater in longans than in mangoes, suggesting that mango leaves are more tolerant of high temperatures than are longan leaves.