| We made a continuous investigation of soil N availability and N mineralization from Oct. 2003 to Oct. 2005 in a mountane moist evergreen broad-leaved forest in Ailao Mountains by using close-top tube incubation method. And, in order to reveal the relation between soil carbon input and nitrogen mineralization, we executed some treatments to the trees investigated including girdling, litter exclusion and trenching. a).girdling to control products of photosynthesis. b).litter exclusion to control aboveground carbon input. c).trenching to control root exudates and root litter. The results were as follows:1. The soil available nitrogen concentrations varied from 22.96 to 68.20 mgN·kg-1 and nitrate ranged from 1.48 to 31.74, ammonia whose variation is from 10.89 to 47.85 and it showed a dominant part (42%-94%) in gross available nitrogen of this ecosystem. Gross available nitrogen varied significantly between dry and wet season. Ammonia climbed to the top at the end wet season and declined to the bottom at the end dry season, while it was different for nitrate, highest at the beginning wet season and lowest at the end wet season.2. Nitrogen mineralization showed a net accumulation in all over the year except the short beginning dry season. Annual amount of net nitrogen mineralization was 159.23kgN·hm-2(for 0-15cm soil layer).3. Not only net nitrogen mineralization rate, but also ammonification and nitrification did not show a significant variation between dry and wet season, this should attribute to the smooth change of the inner soil humid and temperature. For example, the soil moisture held a very high level among the year (1.16±0.13kg·kg-1). Furthermore, the soil inner change lag behind of the air environment.4. Girdling increased the ammount of available nitrogen in the first year, but it disappeared in the second year, and it also increased the ammonia amount...
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