随氮素用量增加，植株下位叶、穗位叶和上位叶的光合速率（Pn）、叶绿素含量（Chl）、可溶蛋白含量（Pro）、Hill反应活性、Ca2+-ATPase活性、Mg2+-ATPase活性和PEPCase活性均不断增大。植株不同叶位Pn和Pro随生长进程均不断下降；不同叶位Chl的变化动态表现为下位叶在各测定时期之间差异较小、穗位叶和上位叶为单峰曲线。Hill反应活力、Ca2+-ATPase活性和Mg2+-ATPase活性的变化规律不同，随生长进程表现不断下降、单峰曲线和双峰曲线等不同形式。各叶位PEPCase活性均表现单峰曲线型变化。随氮素用量增加，叶源量、生物产量和籽粒产量不断增加。适量施氮具有全面改善玉米光合效率和内在生理、生化过程的作用。Ca2+-ATPase活性是影响光反应活力的重要因素；在叶片生长前中期，Pn受到PEPCase的影响较小，主要受到光反应活力和暗反应效率的调控。可采用叶源量作为玉米单株生产力的参考诊断指标。
In order to elucidate the effects of nitrogen on growth and development in summer maize (Zea mays L.), the photosynthesis characteristics regulated by nitrogen application rates in summer maize was studied. The results indicated that the photosynthetic rate (Pn), cholorophyll content (Chl), soluble protein content (Pro), Hill reaction activity, Ca2+-ATPase activity, Mg2+-ATPase activity and PEPCase activity in lower leaf, ear leaf and upper leaf of summer maize cultivar (Ludan 50) all increased, with the increase of nitrogen application amount. With the growth progress, the Pn and pro in all tested leaves gradually decreased. The dynamic changes of Chl in leaves showed different patterns, with little changes at different assaying points in the lower leaf and a single peak curve in the ear leaf and upper leaf. There were different patterns on traits of Hill reaction activity, Ca2+-ATPase activity and Mg2+-ATPase activity, such as the pattern of gradually decrease, single peak curve and double peaks curve. The changes of PEPCase activities in the tested leaves all showed a curve with one peak with the growth progress. With the increase of nitrogen application amount, leaf source capacity, biomass and yield all increased. The results indicated that all photosynthetic characteristics, including Pn, and its related physiological and biochemical parameters could be improved based on application of suitable nitrogen amount. The Ca2+-ATPase activity is one of the important factors to affect the function of photoreaction system in maize. In the experiment, Pn was affected little by PEPCase and largely regulated by function of photo system and dark reaction system in the photosynthetic organ during the early and mid-growth stage. Meanwhile, It is suggested that leaf source capacity could be used as a criteria to evaluate the productivity of single plant in maize.
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