Determinant of photosynthetic capacity in rice leaves under ambient air conditions

Abstract

At the grain-filling stage, net photosynthetic rate (P N), stomatal conductance (g s), and ribulose-1,5-bisphosphate carboxylation efficiency (CE) were correlated in order to find the determinant of photosynthetic capacity in rice leaves. For a flag leaf, P N in leaf middle region was higher than in its upper region, and leaf basal region had the lowest P N value. The differences in g s and CE were similar. P N, g s, and CE gradually declined from upper to basal leaves, showing a leaf position gradient. The correlation coefficient between P N and CE was much higher than that between P N and g s in both cases, and P N was negatively correlated with intercellular CO2 concentration (C i). Hence the carboxylation activity or activated amount of ribulose-1,5- bisphosphate carboxylase/oxygenase rather than gs was the determinant of the photosynthetic capacity in rice leaves. In addition, in flag leaves of different tillers P N was positively correlated with g s, but negatively correlated with C i. Thus g s is not the determinant of the photosynthetic capacity in rice leaves.