Effects of Ellvironmental Conditions of Long and Short Duration on Subsequent Leaf CO2 Assimilation Rates of Rice Plant under a Definite Standard Condition

Photosynthesis of the top leaves of rice plant (var. Norin-17) pretreated with temperature, light intensity and air-humidity of long and short duration was estimated under a definite standard condition (temperature; 28-30°C, light intensity; 7000 f.c.). Shading with 70% light reduction of long duration decreased the dry weight and nitrogen content per leaf area, and depressed the photosynthesis rate probably through changes in structure and cell numbers of the leaf. The effect of short term shading was not clear. Temperature treatments of both long and short period also affected the photosynthesis. In general, the higher temperatures increased the rate although dry weight and nitrogen content per leaf area decreased. 35/30°C seemed to be a little too high for the optimum photosynthesis, with less nitrogell concentration. Under higher temperatures the higher relative humidity of air deprssed the more the photosynthesis with the decrease in dry weight and nitrogen content per leaf area.