抄録
To understand the contribution of each positional leaf to the dry matter production in rice populations or individual plants, net photosynthetic and dark respiration rates of individual leaves of different position and age were measured at four growth stages (reduction division stage, boot stage, heading stage and ripening stage) under full light and mutual shading conditions in the paddy field where different fertilization (high fertilizer, 1 kg/a of each of the three main elements; low fertilizer, 0.2 kg/a of the same elements) and plant spacing (wide spacing, 30 × 22.5 cm; close spacing, 30 × 7.5 cm) were given. 1. The maximum rate of photosynthesis of the uppermost leaf was considered to show the full capacity of production, and the ratio of the photosynthetic rate of each individual leaf to that of the uppermost leaf under the full light condition was regarded to indicate its relative vitality, while the decrease in the photosynthetic rate under mutual shading compared with that under full light was thought to be caused by the external factors. 2. At reduction division stage, the relative vitality of middle and lower leaves to the upper leaf were 80% ca. and 60% ca., respectively; and the external factors lowered the photosynthetic rates under mutual shading by 20% ca. and 35% ca. in the middle and lower leaf, respectively, compared with those under full light. Photosynthetic rate decreased as the time progressed, and the heavily fertilized plants had more efficient leaves in photosynthesis than those lightly fertilized during all the experimental period, but there was no significant difference between those of different plant spacing. In general, photosynthetic rates of individual leaves both under full light and mutual shading conditions decreased about 20% by each descend ofleaf position from the top. 3. Dark respiration rates decreased proportionally to photosynthetic rates during the aging processes of the leaves. The dark respiration rate of the lowest leaf did not exceed 30% of its net photosynthetic rate under mutual shading. Therefore, even the lowest leaf did not seem to be so-called parasitic.
