| Soil microbial biomass is an important component in carbon cycle of the terrestrial ecosystem.And it has a special status in material cycle and energy transformation of forest ecosystem.The study of soil microbial biomass has important meanings in understanding the transformation and cycle of soil nutrient. In the terrestrial ecosystem,the effect of soil microbial biomass to decomposition of organic material and release of soil greenhouse gas has been one of important problems during the global climate change.The study of soil microbial biomass supplies an important base for the influence of predicting the global change on ecosystems.Our research was conducted in a national nature reserve in Fujian Province, which is a typical type in subtropical forest ecosystem.The research on soil microbial biomass in different plant communities along elevation gradients in subtropical forest has not been reported.The article discussed dynamics of soil microbial biomass in different plant communities along elevation gradients and the relationship between soil microbial biomass and different ecological factors in subtropical forest,in Wuyi Mountain.Our object was to provide basic data for carbon flux and its controlling mechanism in subtropical forest ecosystem.The experiment was conducted from April,2006 to January,2007.And the data was seasonally collected in April,July,October,2006 and January,2007.Four different plant communities were chosen such as Alpine meadow(AM,elevation: 2100m),Dwarf forest(DF,elevation:1800m),Coniferous forest(CF,elevation: 1200m)and Evergreen broadleaf forest(EBF,elevation:500m).Three repeated plots in each plant community were set up,respectively,totally 12 plots.The fumigation-extraction method was applied to measure the variation of soil microbial biomass and the dynamic-chamber IRGA method(Lico-6400)was applied to examine the monthly variation of soil respiration.The changes of soil microbial biomass in four different plant communities along elevation gradients,in central subtropical forest in Wuyi Mountain,and the relationship between soil microbial biomass and ecological factors were analyzed in this paper.The results showed: 1.The soil microbial biomass(C,N,P)decreased with the soil depth in the four sites.For example,soil biomass C,N,P in the 0-10 cm soil layer of alpine meadow was 2.33,1.81,2.25 and 6.04,3.68.10.82 times higher than those in the 10-25 cm and 25-40 cm soil layers,respectively,and in evergreen broad-forest,it was 1.47, 1.17,1.13 and 4.82,3.19,4.26 times higher.Soil moisture,TOC,TN and TP contents,pH value were the regulating factors for the variation of soil microbial biomass with the soil depth in the four sites.2.The soil microbial biomass(C,N,P)increased with the elevation gradient, that was AM＞DF＞CF＞EBF.For instance,soil biomass C,N,P of alpine meadow in April,2006 was 2.44,4.12,3.86 times higher than those in evergreen broad-leaf forest,respectively,and soil microbial C,N,P of alpine meadow in January,2007 was 3.56,3.68,2.08 times higher than those in evergreen broad-leaf forest, respectively.Soil moisture,TOC,TN and TP contents were found to be the regulating factors for the variation of soil microbial biomass along the elevation gradient.3.Seasonal variation of soil microbial biomass in EBF,DF,AM was summer＞winter＞spring,and the seasonal variation tendency was not apparent.Soil microbial C,N,P of alpine meadow in summer was 1.36,1.64,1.44 times higher than those in the spring,and in evergreen broad-leaf forest,soil microbial C,N,P was 1.71,2.41,2.37 times higher than those in the spring.Seasonal variation of soil microbial biomass was greatly affected by soil moisture,but not by soil temperature,fine root biomass,litter fall biomass and soil respiration.Our research showed soil microbial biomass decreased with soil layer because of the high nutrition concentration and the comfortable soil conditions in the topsoil; soil microbial biomass increased with the elevation because of the C,N,and P content control and soil moisture variation along the elevation gradient.Variation of soil microbial biomass in the four sites reached the highest in summer and the lowest in spring.These provide basic data for us to indicate carbon flux and its controlling mechanism in subtropical forest ecosystem and further supply important theoretical base for us to predict global climate change.
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