| According to the research on soil nitrogen heterogeneity,nitrogen mineralization and litter decomposition in three forest types (including sub-tropical ever-green hardwood forest in Banruosi,Chinese fir forest in Longchi and Phoebe zhennan forest in Yueliangwan) in Dujiangyan District,the research on soil nitrogen was from June 2000 to June 2001 and the research on litter decomposition was from May 2001 to February 2002,we concluded,1 Incubation soil in field with the method of burying PVC tube covered with plastic film,we measured the change of available nitrogen content and found,although ammonium nitrogen content is higher than nitrate nitrogen content in all the three forest types,the net nitrification rates are higher than net ammonification rates under both the ever-green hardwood forest in Banruosi and Phoebe zhennan forest in Yueliangwan,howerer,under the Chinese fir forest in Longchi,the net nitrification rate is equal to net ammonification rate. The enhancement of net nitrification rate means degeneration of soil. The net nitrification rate and net nitrification rate are different in the same period of time,which means the ammonification and nitrification are controlled by different groups of microorganisms.2 The net nitrification rates and net ammonification rates are all negatively correlated to soil temperature to some extent and the net ammonification rate is negatively correlated to soil temperature under the Chinese fir forest in Longchi with p<0.05. Nitrification rates are positively correlated to soil temperature to some extent in all the three forest types. That shows,although temperature is one of key factors to affect the net nitrification rate,net ammonification rate and net mineralization rate,it will affect the three processes through affecting the group,number and activity of microorganism to achieve the result,because of the difference of environment,the effect of temperature will changed greatly. Besides,the water content also has some effects on net nitrification rate,net ammonification rate and net mineralization rate although its effects are not remarkable.3 There are different biodiversity in different forest types. Biodiversity will affect theforest ecosystem soil nitrogen cycling greatly though affecting the litter account and quality,the composition and character of microorganism groups and vegetation coverage et al. The lost of biodiversity will lead to the increase potential of soil inorganic nitrogen (especially nitrate nitrogen) loss,gradually reducing the soil inorganic nitrogen pool,so the soil available nitrogen content will decreased greatly.4 Ammonium nitrogen and nitrate nitrogen compose most of the soil inorganic nitrogen. But the nitrate nitrogen is easy to be washed,lost from the earth's surface current,absorbed by plants or lost by denitrification,so nitrate nitrogen often exhibit large fluctuation and nitrate nitrogen content are ofern lower than ammonium nitrogen content greatly. The proportion of nitrate nitrogen content to total available nitrogen content is different among different study site and time.5 Carry out the experiment of litter decomposition with net bag method,we found that the decomposition rate of the mixed litter is slower than the theoretical value calculated by proportion of composition of different litters. That means that the mixture of Castanopsis spach Cyclobalanopsis niganensis Machilus pingii Symplocos la in this experiment does not promote the rate of decomposition.6 Soil water content is correlated to mass loss during decomposition greatly,while temperature does not affect mass loss to such extent. But as to the concrete element such as C and N,the decomposition is controlled by more complex mechanism,maybe including the difference of soil microorganism groups for decomposing and the difference of physical,chemical character of soil,and soil water content maybe be less important in such condition.7 The initial C/N concentration ratio in litter affect decomposition remarkably,and negatively correlated to con...
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