Photosynthetic response to high temperature under different levels of irradiance in mango (Mangifera indica L.).
Harvinder Talwar, Abdul Karim, Fukamachi H., Tsukaguchi T., Komori S., Hidaka T.
Author Affiliation: ICRISAT, Genetic Resources and Enhancement Program, Patancheru 502 324, A.P., India.
Japanese Journal of Tropical Agriculture 45 : 77-83
Abstract : The coincidence of high temperature and different levels of irradiance is a common feature of tropical and subtropical regions. The objectives of the present study were to examine the effects of high temperature stress under different levels of irradiance on (1) photosynthetic rate and gas exchange characteristics and (2) chlorophyll fluorescence characteristics in mango (M. indica cv. Irwin). Three-year-old grafted mango trees grown in a plastic house were treated in three growth chambers maintained under three different combinations of day/night temperature and light irradiance; day/night 30/25°C + 600 µmol m-2 s-1 (T1), 40/25°C + 600 µmol m-2 s-1 (T2) and 40/25°C + 200 µmol m-2 s-1 (T3). The CO2 exchange characteristics indicated that the changes in the temperature regime from 30/25°C to 40/25°C affected the net photosynthetic rate, stomatal conductance, transpiration rate and intercellular carbon dioxide concentration. On the other hand, the changes in light irradiation did not affect these gas exchange characteristics though the net photosynthetic rate decreased under lower radiation level significantly compared with higher irradiation level for 52 and 92 h of treatment. The efficiency of photosystem II (F'v/F'm) and variable fluorescence (F'v) during the steady state was significantly different among the three treatments. The increase in temperature to 40/25°C at 600 µmol/m-2 s-1 (T2) resulted in a significant decrease in the F'v and F'v/F'm ratio compared to T1. But when the light irradiance was reduced to 200 µmol/m-2 s-1 at 40/25°C (T3), the F'v and F'v/F'm ratio increased significantly compared to the values in the plants grown under T1. These results suggested that the changes in irradiance affected the F'v and F'v/F'm ratio more than the changes in temperature. The initial fluorescence were opposite to those of F'v under the three treatments. The electron transfer decreased abruptly when the irradiance level decreased from 600 µmol m-2 s-1 to 200 µmol m-2 -1 even when the temperature increased to 40/25°C. However, when the temperature increased from 30/25°C to 40/25°C, without changes in the irradiance level, the electron transport first increased marginally and then decreased abruptly. Our results indicate that stomatal factors are sensitive to changes in the temperature while the non-stomatal factors to changes in the irradiance.