Abstract: Calamogrostis angustifolia is one of the representative plants in Sanjiang Plain. Under controlled water levels, the population densities in C. angustifolia and C. angustifolia-Carex communities were investigated, and the relationships between population density and water level were analyzed. The results showed that the seasonal dynamics of C. angustifolia population density in C. angustifolia communities possossed a bimodal curve at water levels from 0 to 20 cm, while that C. angustifolia-Carex communities displayed abimodal curve at -10, 0 and 30 cm water levels. In C. angustifolia communities, except at 10 and 20 cm water levels, the higher the water level, the lower the population density was. While in C. angustifolia-Carex communities, the population density was the highest at 0cm water level, with no linear relationship observed between the population density and water level. The C. angustifolia population densities of the two communities had a distinct change at 10 cm water level,i.e., with an initial rapidly increase, then slowed down, and then increased again. There was a significant negative correlation between the population density and water level, and thus, the C. angustifolia population density at different water levels could be estimated through fitted polynomial equations.

Key words: Pinus koraiensis, Elevated CO₂, Net photosynthetic rate, Stomatal conductance, RuBP, Soluble sugar, Chlorophyll