Relation between Environmental Conditions and Production-and Consumption Activities of Individual Leaves in the Population of Rice Plant in a Paddy Field : I. Changs in photosynthesis and dark respiration of individual leaves under field conditions

[摘要] To understand the life of rice plant more actually, photosynthetic and respiratory rates of individual leaf of different age were measured for 7-8 days continuously at each of the 3 growth stages (panicle formation stage, boot stage and ripening stage) under field conditions and their relationships with the environmental conditions were discussed. 1. The ambient CO2 concentrations at 3 layers (80, 50 and 20 cm from the ground level, respectively) in the canopy were high during night, probably being relatcd with the very low wind speed. During daytime, CO2 concentration of middle and low layers was lower than that of the upper layer as much as 25 ppm, but all the layers showed almost similar changing patterns of CO2 conccntration in different days or different seasons, probably due to adequate influx of air into the canopy. 2. Daily or seasonal differences in air temperature were great, but diurnal changes during active photosynthesis (8:00-17:00) were small (about 2-5°C). Dark respiration was very closely related with night temperature. 3. Both on fine and cloudy days, photosynthetic rate changed with light intensity, but responses were less sensitive in lower leaves. However, on clear days, photosynthesis remained almost constant during 9:00 to 14:00, irrespective of the light intensity, excluding its sudden drop by cloud. The photosynthesis of the uppermost leaf was saturated at the incident light intensity of 70 klx ca., the lower leaves at 50 klx ca. and the middle leaves at the intermediate intensity. 4. The middle and lower leaves photosynthcsized ca. 60-70% and ca. 35-50% of the amount for the uppermost leat respectively, and the percentages were a little higher on cloudy days than on fine days. During night, they respired 80-90% and 50-60%, respectively, compared with the uppermost leaf (100%). The ratios of dark respiration to photosynthesis were about O.1 on clear days; but they were a little higher on cloudy days and for the lower leaves. The lowest leaves at the ripening period which were just prior to dying consumed during night less than half of the photosynthate produced during daytime even on cloudy days, suggesting that even those old leaves under strong shade may not be "parasitic" in the sense of consuming more than production.

[学科分类] 农业科学（综合）