Relation between the depression of photosynthesis by low night temperature and the root activity of rice plant.

Abstract

Five rice cultivars, three Japonica and two hybrids of Japonica-Indica, were grown in pots to examine the influence of low night temperature (10°C) on photosynthesis and transpiration during the period from young panicle formation to middle of the ripening stage. Photosynthesis and transpiration were depressed from 3 to 46% by low night temperature when compared with those under natural night temperature. The depression was due to increased stomatal resistance. The percentage of depression of photosynthsis and transpiration were highly correlated (0.939) with each other. The relative value (treated/non-treated) of photosynthesis had high multiple regression coefficient (R=0.880) with both root respiratory rate and specific leaf area (SLA). The relative value of transpiration had high multiple regression coefficient (R=0.861) with root respiratory rate, SLA and leaf area per stem. The result shows that root respiratory rate was supported by its nitrogen and sugar contents, and also; SLA had a highly negative correlation to leaf respiration. Thus, a rice plant, having active root respiratory rate and low SLA which in turn has high leaf respiratory rate is capable to be released from low night temperature stress the next morning.