Studies on dry matter production of soybean plant. : IV. Photosynthetic properties of leaf as subsequently affected by light condition.

Soybean variety Shirobana-Sai-No. 1 growing in pot was subjected during the growing period of 5th or 6th leaf on main stem to various shading treatments. Photosynthetic capacity of the leaves were measured under various light intensity, and light-photosynthesis curves obtained with the leaves of different treatments were further investigated to know the photosynthetic properties of leaf as subsequently affected by light condition. The results obtained were as follows: (1) The photosynthetic capacity at higher light intensity decreased with decrease in light intensity in a given period by shading. (2) The earlier the beginning of shading, the more the depression of photosynthetic capacity at higher light intensity, though the shading after the leaf had fully expanded also caused a somewhat depression of photosynthetic capacity. (3) Cessation of shading showed a trend of recovering photosynthetic capacity. The recovery was complete when the shading ceased at the time of unfolding of the leaf, whereas it was incomplete for the cessation at the time of full expansion of the leaf. (4) Admitting some exceptions, photosynthetic capacity at lower light intensity increased by shading, while decreased by cessation of shading. (5) Respiratory activity of the leaves decreased by shading, while increased by cessation of shading.