Photosynthesis and Transpiration in Rice as Influenced by Soil Moisture and Air Humidity

Abstract

The paper describes the effect of soil moisture content and air humidity on CO,2 exchange ( PN ), C02 diffusion resistance (Cr) and transpiration (E) in four varieties of japonica rice ( Oryza sativa L.). A decrease in soil moisture content reduced the rate of photosynthesis to a varying degree in the varieties. Reduction in photosynthesis was attributed to increase in Cr. The effect of low soil moisture on photosynthesis and C02 diffusion was further intensified by decrease in air humidity. By maintaining a high humidity in the air around the leaves however, the effect of soil moisture deficiency was reduced considerably, except in Rikuto Norin 21 which was very sensitive to soil-moisture deficiency alone. Dryness of the air enhanced the transpiration rate, although the increase was relatively less in the plants facing a simultaneous water crisis at the root surface. In plants growing under flooded conditions, a decrease in air humidity caused a slight depression in Ps despite the simultaneous decrease in Cr.