Abstract
Old (resistered before 1945) and new (resistered after 1950) rice varieties were compared about single-leaf photosynthesis (CER) and stomatal conductance (gs). (1) At the heading stage, no or little difference in CER was observed between the old and new variety groups. However, at the ripening stage, CER was clearly higher in new verieties. The new/old ratio in CER was 124.4% in the average for three years. (2) gs was higher in the new variety groups than that in the old one at the ripening stage. (3) In most cases when CER and gs were measured, correlation coefficients more than +0.8 were obtained between the two, suggesting the varietal difference in CER was mainly caused by that in gs. However, the ΔCER/Δgs ratio in the ambient air humidifying treatment (ΔCER and Δgs are incremcnts in CER and gs respectively caused by the treatment) was smaller than the regression coefficient for CER vs gs in the varietal difference and the former was equivalent to ca. 70% of the latter in the average for 12 days. The findings suggested ca. 30% of the apparent effect of gs on CER was attributable to the effect of the mesophyll photosynthetic activity which changed in parallel with gs.
