| A field experiment with micro-plots was conducted under rain-preventing condition for studying the effects of N supply on some physiological characteristics related with photosynthesis of maize. With application of different rates of N and water, determinations were made for the ratio of free water to bound water in leaves, cell sap concentrations, stomatal conductance, intercellular CO2concentrations, RuBPCase activity, chlorophyll contents, leaf photosynthesis rate at different time, and finally the biomass yields. The results showed that the effect of N on photosynthesis was determined by water supply. When water supply was relatively sufficient, input of N raised the ratio of free water to bound water in leaves, decreased sap in diachyma cells and intercellular CO2concentrations, raised stomatal conductance, RuBPCase activity and chlorophyll contents. This was not only beneficial to improvement of the stomatal factors but also to the non-stomatal factors, and consequently resulted in significant increase in photosynthesis rate and biomass production. When water was slightly stressed, input of N decreased stomatal conductance, and increased the resistant force for CO2entering stomata, being detrimental to photosynthesis, but it raised the ratio of free water bound water, decreased in diachyma cells sap concentration and intercellular CO2concentration as well as RuBPCase activity and chlorophyll contents. In this case, N input mainly affected the stomatal factors of photosynthesis, but the non-stomatal factors were not decreased, but increased, and therefore photosynthesis rate and biomass were raised. In contrast, when water was seriously stressed, input of N did not only inhibit the stomatal factors but also seriously inhibited the non-stomatal factors as major causes, resulting in photosynthesis rate and biomass decline. The effect of N input on photosynthesis being dependant on water supply provides a basis for regulation of N nutrition. |