Abstract: A simulation study was made on the responses of biomass of Deyeuxia angustifolia and soil active carbon pool in Sanjiang Plain of Northeast China to simulated nitrogen deposition. Two water conditions (W₁: nonflooded, W₂: flooded) and four N treatments (equivalent to 0, 1, 3, 5 g N·m^-2·a^-1 nitrogen deposition rate) were installed. The results showed that under effects of nitrogen deposition, the total biomass, aboveground biomass, and root biomass of D. angustifolia were higher than the control, and the increment of root biomass was the highest. Both the carbon content and its allocation proportion in D. angustifolia root increased significantly, while the carbon content in aboveground part decreased dramatically (P<0.05). Nitrogen deposition also had significant effects on soil active carbon pools, and the contents of various fractions in the carbon pool were the highest in treatment 5 g N·m^-2·a^-1. The responses of various fractions in soil active carbon pool to nitrogen deposition followed the sequence of carbohydrate carbon＞labile carbon＞dissolved organic carbon＞microbial biomass carbon, and the interaction between nitrogen deposition and flooded water condition facilitated the release of soil active carbon. Regression analysis indicated that there were significant correlations between soil active carbon pools and plant indices of D. angustifolia. Nitrogen deposition could enhance the biomass of D. angustifoliat and soil active carbon content.

Key words: dark respiration, environmental factor, vegetation productivity, carbon cycle.