Abstract
Two cultivars of potted rice plants were given various treatments, such as, 10 cm depth inundation, high water parcolation (30 mm/day) and excision of lower leaves below top three leaves, in order to change the respiratoy rate of roots. Photosynthesis and dark respiration were measured by the assimilation chamber method under the given conditions of temperature range from 20°C to 40°C during 4 hours at the time of young panicle formation, heading and mid-period of ripening. Immediately after this measurement, the roots were sampled with thoroughly washing out soil and the root respiration in normal air was measured by chamber method. At the time of young panicle formation, the respiratory rate of younger roots from upper three nodes at the base of stem showed much higher activity than that of older roots on lower nodes, however, such diflbrences were not noticed during the period after heading. The ratio of gross photosynthesis of 30°C to 40°C showed a high positive correlation to the respiratory rate of root ; the plants with lower rate of respiration exhibited strongly depressed photosynthesis at high temperature of 40°C perhaps due to thermoactivc closure of stomata. The depression observed at high temperature appears to be caused by water deficit in leaves due to inferior water absorption, since the transpiration efticiency at 30°C was quite dependent on the respiratory rate of roots. Multiple regression analysis of root respiration, nitrogen and sugar content in root revealed that the respiratory rate of root had high positive correlation with the nitrogen as well as the sugar content of the roots. The nitrogen content in root was swayed by nitrogen concentration at the top whereas the sugar content was parallel to net photosynthetic, activity of the plant which in turn is capable of expressing by nitrogen content in leaves of the plant.
