Abstract: Primary productivity by photosynthesis is the support and basic drive for the beginning and evolution of ecosystem productivity. Photosynthesis usually changed with variation of environmental conditions. In this study, we used leaf level gas exchange method (by Licor-6400) to study the diurnal changes of photosynthesis in rice, soybean and maize at different developmental stage, and we found that: There was noon depression of photosynthesis for all C₃ plants at all developmental stages. Such depression was owing to stomatal and non-stomatal effects separately, or combined. The stomatal effects were caused by the high temperature, which resulted feedback inhibition effects owing to the increase of transpiration. The responses of C₃ crops (rice, soybean) to light were different in the morning and afternoon. The light use efficiency was higher in the morning and apparent quantum yield owing the photosynthetic feedback inhibition, contrasting to that in the afternoon. The stomatal or non-stomatal effects and feedback inhibition effect were the main reasons to "hysteresis". While, there was no apparent noon depression C₄ crop (maize), as well as "hysteresis", showing great acclimation of C₄ crop to high temperature.

Key words: Rice(Oryza sativa L.), Soybean(Glycine max L.Merrill), Maize(Zea mays L.), Photosynthesis, Stomatal limit, Hysteresis

CLC Number: 

• S511.01

• S565.1

• S513.01