Variations Of Soil Labile Organic Carbon Along The Elevation Gradient In Wuyi Mountain

In global carbon cycling,the variation of soil carbon is the most complex and uncertain part.The slight changes in soil carbon pool may greatly affect the concentration of CO₂ in the atmosphere because of the huge flux between soil and atmosphere.Though soil labile organic carbon only takes up a small portion of organic carbon,it is the most active fraction with rapid turnover rate,which could pre-indicate the slight variations of the soil than the total organic carbon could,it also directly participate in soil biochemical processes.Thus,it greatly affects the balancing of carbon cycling.Therefore,study on the content and distribution of labile organic carbon at mountainous area is of great importance in indicating the discipline of soil carbon cycling of a certain region and forecasting the trend of global climate change.The effect of spatial variations to the processes in ecosystems is one of the major topics of ecological study at present,and the variations along the elevation in mountainous area provide good conditions to study the spatial heterogeneity of ecosystems.Thus,the experimental sites were set in the Wuyi Mountain National Reserve Area,where annually average temperature,relative humidity,fog days, precipitation,are 12-18℃,82%-85%,more than 100 days,and about 2000 millimeters,respectively.The typically regional forest is evergreen broad-leaf forest and the natural resources are very rich.The forest types along the elevation gradient are:evergreen broad-leaf forest(EBF),coniferous forest(CF),sub-alpine dwarf forest(SDF),alpine meadow(AM),respectively.Experimental sites were randomly set in the four vegetation communities in order to examine the temporal and spatial variations of soil labile organic carbon(SLOC)and its main regulating factors,so as to indicate the response of soil carbon along the elevation gradient to global climate change.From April 2006 to January 2007,microbially available carbon(MAC),microbial biomass carbon(MBC),readily oxidation carbon(ROC), water-soluble organic carbon(WSOC)together with several regulating factors,such as total organic carbon(TOC),total nitrogen(TN),litterfall biomass(LFB),fine root biomass(FRB),soil temperature and moisture were measured.The results indicated that:Spatial variations of MAC,MBC,ROC,WSOC increased with the elevation gradient,and decreased with the soil layer.The amount of labile organic carbon in AM was significantly greater than those in the other three communities.The turnover rate(κ)of MAC indicated that the decomposition speed of MAC decreased with the elevation gradient and the soil layer.Soil labile organic carbon(MAC,MBC,ROC,WSOC)correlated positively with total organic carbon,total nitrogen,FRB,LFB,soil moisture,and negatively with soil temperature and moisture,soil respiration.Moreover,WSOC correlated positively with total sulfur,and negatively with pH value.The four kinds of labile carbon correlated positively with each other,and the best correlation was between MAC and MBC(R²=0.942).The ratio order of the four kinds of labile carbon to TOC was:ROC＞MAC＞MBC＞WSOC.Seasonal variations of MAC and MBC were:summer＞spring＞fall＞winter.The variations of MAC and MBC were significantly affected by seasonal variations of soil moisture;soil temperature greatly affected MAC but not MBC.The variations of MAC and MBC were not apparently influenced by the variations of FRB and LFB. In one season,however,the four kinds of labile carbon correlated positively with FRB and LFB.The decomposition of SLOC is a complex biological process and is regulated by many factors.Because there is no specific definition and measurement for SLOC, how to evaluate the function and significance of measured labile organic carbon in terrestrial ecosystem's carbon cycling and regional carbon balancing still needs a further study.