Abstract: Seasonal changes in the photosynthetic characteristics of Ammopiptanthus mongolicus (Maxim.) Chen f. were studied. When the net photosynthetic rate decreased with the elevation of air temperature, the stomata conductance and stomatal limitation value tended to decline simultaneously, while the intercellular CO2 concentration was increased. According to the two criteria discriminating the stomatal limitation of photosynthesis suggested by Farquhar and Sharkey, the seasonal changes in these parameters indicated that the decrease in Pn, may not be due to stomatal factor. These studies proved that the relative contents of the large subunit of Rubisco and the photochemical activities correlated with the seasonal changes in the net photosynthetic rate, which may show that these two factors contribute primarily to the seasonal changes in CO2 assimilation.

Key words: Net photosynthetic rate, Stomatal conductance, Intercellular CO2 concentration, Stomatal limitation value, Rubisco, Electron transport activity