Abstract: Forest soil is one of the main sources of greenhouse gases CO₂, CH₄, and N₂O. By using static chamber and GS technique, this paper measured in situ the CO₂, CH₄, and N₂O fluxes of Acacia crassicarpa plantation in Heshan Hilly Land Interdisciplinary Experimental Station under Chinese Academy of Sciences (CAS), and studied the soil CO₂, CH₄ and N₂O emissions from the plantation under effects of understory removal and Cassia alata addition. The CO₂ flux of the plantation maintained at a higher level during rainy season but decreased obviously in dry season, while the CH₄ and N₂O fluxes varied widely from September to November, with the peaks in October. Under the effects of understory removal and C. alata addition, the soil in the plantation could be a sink or a source of CH_4, but consistently a source of CO₂ and N₂O. Understory removal enhanced the soil CO₂ emission (P<0.05), C. alata addition increased the soil CH₄ emission (P<0.05), while both understory removal and C. alata addition increased the soil N₂O emission (P<0.05). Surface soil temperature, moisture content, NO₃^--N concentration, and microbial biomass carbon were the main factors affecting the soil CO₂, CH₄ and N₂O emissions.

Key words: greenhouse gas emission, Acacia crassicarpa plantation, understory, Cassia alata, Bacillus, corn straw, lignocellulose, biodegradation.