Single leaf photosynthesis of rice plants under field conditions. VII. Evaluation of the degree of real contribution of stomatal conductance to the individual variation and to the depression with time of day in single leaf photosynthesis.

Abstract

It was previously, shown that the individual variation and the depression with time of day in single leaf photosynthesis (CER) were closely correlated with those in stomatal conductance (gs). However, when gs varies in parallel with photosynthetic activity of mesophyll, a close positive correlation can exist between gs and CER even if mesophyll activity is the major factor in those kinds of CER variations. In such a case, it looks as if gs were the only one or major factor bringing the CER variations. The objectives of this study was to estimate the degree of real contribution of gs to the CER variations on the assumption that an ambient air humidifying treatment increases only gs without affecting mesophyll photosynthetic activity. The conclusions are as follows : 1) One half of the individual variation in CER among flag leaves was caused really by the variation in gs, and the other half, by that in mesophyll photosynthetic activity varying in parallel with gs. 2) The depression in CER with time of day was caused mainly by a depression in gs and to a small extent, by that in mesophyll photosynthetic activity.