A model explaining genotypic and ontogenetic variation of leaf photosynthetic rate in rice (Oryza sativa) based on leaf nitrogen content and stomatal conductance

Abstract

• Backgrounds and Aims: Identification of physiological traits associated with leaf photosynthetic rate (Pn) is important for improving potential productivity of rice (Oryza sativa). The objectives of this study were to develop a model which can explain genotypic variation and ontogenetic change of Pn in rice under optimal conditions as a function of leaf nitrogen content per unit area (N) and stomatal conductance (gs), and to quantify the effects of interaction between N and g s on the variation of Pn. • Methods: Pn, N and gs were measured at different developmental stages for the topmost fully expanded leaves in ten rice genotypes with diverse backgrounds grown in pots (2002) and in the field (2001 and 2002). A model of Pn that accounts for carboxylation and CO2 diffusion processes, and assumes that the ratio of internal conductance to gs is constant, was constructed, and its goodness of fit was examined. • Key Results: Considerable genotypic differences in Pn were evident for rice throughout development in both the pot and field experiments. The genotypic variation of Pn was correlated with that of gs at a given stage, and the change of Pn with plant development was closely related to the change of N. The variation of gs among genotypes was independent of that of N. The model explained well the variation in Pn of the ten genotypes grown under different conditions at different developmental stages. • Conclusions: The response of Pn to increased N differs with gs, and the increase in Pn of genotypes with low g s is smaller than that of genotypes with high gs. Therefore, simultaneous improvements of these two traits are essential for an effective breeding of rice genotypes with increased Pn. © The Author 2007. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved.