Studies on Yield-Forecast of Principal Crops : 1. Photosynthesis in rice plants under field conditions with special reference to its changes with growth.

摘要

Photosynthesis in rice plants grown on a field was studied using Norin 37 variety in 1955. Apparent rates were measured by comparing the CO2 content in normal air with that in the air stream from a blower passing through a plant chamber which covered four plants under it. CO2 analyzer with a slight modification of that described by CHAPMAN and LOOMIS (1953) was used. The results obtained were as follows: 1) Diurnal clranges in the rate of photosynthesis showed a tropzoid and a saturation point was observed on fine days during the period from tillering to booting stages. With the progress of plant growth, however, the saturation point disappeared and there occured a complete parallel relation between the photosynthetic curves and light intensities, up to the time of heading. 2) Changes in light intensity and the rate of photosynthesis associated with growth stages were shown in fig. 3. The saturation point which was comparatively low during the tillering stage, ascended gradually with the progress of growth, and disappeared completely at the atage just before heading. The results seemed to indicate that the plant under field conditions had different demand for light intensities for the maximum photosynthetic activity at different growth stages. 3) The seasonal changes in the rate of photosynthesis are presented in fig. 5. The first maximum point appeared immediately before the stage when the young panicles begin to differentiate. During the subsequent elongating stage the rate gradually decreased and again reached the 2nd maximum point at the boot ing stage, followed by reduction that continued until the time immediately after hegding. At the earlier milk stage, or when the carbohydrates began to be translocated to ears from the culm and the leaf sheath, the rate was recovered.