Studies on the Seed Production of Soybean : II. Effect of three major nutrient elements supply and leaf age on the photosynthetic activity and diurnal changes in photosynthesis of soybean under constant temperature and light intensity.

Abstract

Using the intact leaves of non-nodulated soybean variety, T 201, the effect of three nutrient elements supply on the photosynthetic rate of leaves was investigated. And then, using the mature intact leaves of soybean variety, Norin No. 2, the apparent photosynthetic rate was continuously measured for 24 hours under constant temperature, light intensity, using the out door air as CO₂ source. The following results were obtained. 1. Soybean plants were supplied with different amount levels of nitrogen, phosphorus and potassium, respectively. It was found that nitrogen gave limiting influence to photosynthesis and the photosynthetic rate was promoted with increasing nitrogen content in leaves. While the rate of photosynthesis was scarcely affected by phosphorus, potassium and water content. In most case, respiratory rate showed a close correlation with photosynthetic rate. 2. The photosynthetic rate of leaves attained to the highest value at the time of completion of leaf expansion. The highest value continued for about one week, and afterward activity declined gradually. 3. The diurnal fluctuation in the photosynthesis of leaves showed a close relationship with CO₂ concentration in air. But, even when kept under constant temperature, light intensity and CO₂ concentration, it was observed that there existed the endogenous rhythm of photosynthetic rate which declined at night and recovered in the morning.