Intraspecific variation in photosynthetic nitrogen-use efficiency is positively related to photosynthetic rate in rice (Oryza sativa L.) plants

To explore the natural variation in leaf photosynthesis and investigate its relations with leaf nitrogen (N) status, 121 rice cultivars were pot-grown and their leaf photosynthetic rate (P-N) and N content were measured on the flag leaves at heading stage before anthesis. The results showed that there were substantial natural variations in P-N, leaf N content based on leaf area and leaf mass, and photosynthetic N-use efficiency (PNUE). P-N ranged between 15.4 and 32.6 mu mol m(-2) s(-1); P-N and PNUE of four widely grown cultivars in China were significantly lower than PN and PNUE of the cultivar Nancay PA, which possessed the highest values for P-N and PNUE. Moreover, PNUE was positively related to P-N across cultivars, the high PNUE was related to high stomatal conductance, high transpiration, and low leaf mass per area. We concluded that intraspecific variation in PNUE is positively related to P-N in rice plants.