Photosynthetic Characteristics of Flag Leaf in Rice Genotypes with Different Nitrogen Use Efficiency

Abstract To identify the photosynthetic mechanism of nitrogen (N) absorption and utilization in different rice ( Oryza sativa L.) genotypes, relationships between photosynthetic characteristics of flag leaf and N use efficiency were investigated in 6 N-efficient and 6 N-inefficient rice genotypes with variable N use efficiency. The abilities of seed setting of the genotypes were also analyzed. The N application rate was 225 kg ha −1 for all genotypes. During grain filling, chlorophyll content, N content, net photosynthetic rate, photosynthetic function duration, maximum photochemical efficiency ( F v / F m ), potential photochemical efficiency of photosystem II ( F v / F o ), actual photochemical efficiency of photosystem II ( Φ PSII ), photochemical quenching coefficient ( q P ), and nonphotochemical quenching coefficient ( q N ) of flag leaf were obviously higher in the N-efficient genotypes than those in the N-inefficient genotypes. All these indexes were positively correlated with N use efficiency and seed-setting ability. Compared with the N-inefficient genotypes, the N-efficient genotypes had more favorable characteristics of photosynthesis and longer photosynthetic function duration. Besides, their PSII was steady for the large potential of converting light energy into electrochemical energy, and nonphotochemical quenching could also protect the photosynthetic apparatus. The accumulation of photosynthate and the seed-setting ability were enhanced in the N-efficient genotypes compared to the N-inefficient genotypes. Simultaneously, the N absorption and utilization of N efficient genotypes were improved through feedback regulation of roots and shoots.