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

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 (Fv/Fm), potential photochemical efficiency of photosystem II (Fv/Fo), actual photochemical efficiency of photosystem II (ΦPSII), photochemical quenching coefficient (qP), and nonphotochemical quenching coefficient (qN) 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.

摘 要选用氮肥利用高效型和低效型具有代表性的12个粳稻品种, 研究了225 kg hm−2 施氮条件下水稻剑叶光合特性的差异及其与氮肥利用效率、水稻结实性的相互关系。结果表明, 齐穗后氮高效基因型水稻的叶绿素含量、叶片含氮量、净光合速率、光合功能期和叶绿素荧光动力学参数中的最大光化学效率(Fv/Fm)、PSII的潜在活性(Fv/Fo)、实际光化学效率(ΦPSII)、光化学猝灭系数(qP)和非光化学猝灭系数(qN)均显著高于氮低效基因型。相关性分析表明，齐穗后不同时期，剑叶中叶绿素含量、叶片含氮量、净光合速率、剑叶的光合功能期和叶绿素荧光动力学参数值(Fv/Fm、Fv/Fo、ΦPSII、qP、qN)与水稻的氮肥利用效率、结实性均呈极显著的正相关。由此说明，与氮低效基因型相比，氮高效基因型水稻生育后期具有较好的光合特性，较长的光合功能期；同时，其PSII反应中心更加稳定，具有更大的光能转化为电化学能的潜力，非光化学猝灭对光合机构也有更好的保护作用。因而，其在促进植株光合物质积累、提高结实性的同时, 能通过地上部与地下部的调节反馈增强植株对氮肥的吸收利用。