Abstract: The difference in leaf photosynthesis and senescence characteristics of lowyielding and low Nefficiency, highyielding and medium Nefficiency, highyielding and high Nefficiency rice cultivars was investigated using six representative japonica varieties under their optimum N levels, respectively. The results were as follow: compared with lowyielding varieties, the highyielding ones showed higher  population leaf area index (LAI), higher leaf area rates of productive tillers and top 3 leaves, higher flag leaf chlorophyll content (SPAD value)and net photosynthetic rate, and slower senescence of leaves. Among highyielding varieties, as the nitrogen efficiency increased, the population leaf area index (LAI) reduced at the early and middle growth stages (Nn, jointing, and full heading), and increased at maturing. Though with no significant changes during early grain filling stage (0-10 days after full heading), the net photo synthetic rate remarkably increased in middle and late grain filling stages (20-40 days after full heading), which could mainly be attributed to the less breakingdown of chlorophyll, ensuring the higher CO2 assimilation capacity of leaves, the higher SOD activity providing strong antioxidant capacity of the plant, and the lower MDA content implying the less damage degree of membrane lipid. It could be one promising method for further improvement in nitrogen efficiency of highyielding rice varieties to reasonably control the growth of nonproductive and inefficient leaf area before heading, thus properly reducing population leaf area scale before heading and effectively delaying leaves senescence after heading to ensure sustained higher chlorophyll content and net photosynthetic rate of leaves.

Key words: rice, highyielding and high Nefficiency, leaf characteristics, photosynthesis, senescence

摘要： 选用6个具代表性的低产氮低效型、高产氮中效型和高产氮高效型粳稻品种，在各自最适氮素水平下，研究了叶片光合、衰老特性的差异及其与氮效率的关系。结果表明，高产类型群体叶面积指数(LAI)、高效叶面积率及有效叶面积率、剑叶叶绿素含量(SPAD值)和净光合速率以及剑叶超氧化物歧化酶(SOD)活性均显著高于低产类型品种，丙二醛(MDA)含量显著低于低产类型。高产品种间比较，随着氮效率提升，生育前中期(够苗、拔节、齐穗期)群体叶面积指数下降，成熟期上升；灌浆前期(齐穗后0 d~10 d)剑叶净光合速率并未明显变化，灌浆中后期(齐穗后20 d~40 d)显著增高，主要原因如下：叶绿素分解少，保证了叶片对CO2的高同化能力；SOD活性高，保证了植株更强的抗氧化能力，MDA含量少，膜脂破坏程度低。说明抽穗前合理控制无效及低效叶面积生长以适当减小群体叶面积规模，抽穗后有效延缓植株衰老，以保证叶片持续较高的叶绿素含量和净光合速率，是促进水稻高产品种进一步提升氮效率的重要途径。

关键词: 水稻, 高产高效, 叶片, 光合, 衰老