Studies on Dry Matter Production of Soybean Plant : I. Ontogenic changes in photosynthetic-and respiratory capacity of soybean plant and its parts.

Abstract

Soybean plants, var Shirohara-Sai No. 1 were cultivated under field condition, and the various, characters related to photosynthesis and respiration were observed at about two weeks intervals. The results obtained are as follows; (1) Total area of green leaves increases upto the begining of ripening and then decreases because of senescence. (2) Photosynthetic activity (photosynthetic rate per unit area of leaf) of individual leaves of main stem increases with the development of the leaves and after attaining a maximum value, declines with progress of senescence. These processes proceed successively from lower leaves to upper leaves. However, in several upper leaves, senescence occurs simultaneously with advancement of maturation irrespective of the time of formation. The maximum value of photosynthetic activity of each leaf rises with the rise of the position of leaf on the main stem. (3) Photosynthetic activity of the leaves of main stem is higher than that of the leaves of branches. (4) Total photosynthetic capacity of leaves (sum of photosynthetic rate of individual leaves on plant) increases with growth upto the begining of ripening and then decreases. (5) Green pods have somewhat photosynthetic capacity but is small compared to that of the leaves. (6) Green part of stem has photosynthetic capacity, too, but of lower rate than that of pods. (7) Respiratory activity (respiration rate per unit weight of tissue) is highest in leaf, lowest in stem and intermediate in root. Respiratory activity of young pods is very high, but with progress of ripening it declines rapidly. (8) At the first half of the growth period, respiratory capacity (total amount of respiration of each part of plant) is largest in leaves and is relatively small in other parts. At the second half of the growth, both pods and leaves are predominant in respiratory capacity.