| To increase our undersanding of the impact of soil organic carbon on glaobal changeand the contribution of greenhouse gas, and provide the scientific data for undersanding themechanism of the impact of land use change on soil organic carbon, soil samples werecollected from four land use/cover types at Miyaluo in subalpine area of Western Sichuan,including primitive Abies faxoniana forest, 45-year-old planted spruce forest (Picealikiangensisi var balfourianan), 25-year-old planted spruce forest and cropland. The soilphysicochemical properties, microorganism composition, enzymes activity and soil labileorganic carbon and their seansonal changes were analyzed. All the soil sections weredivided into five layers according to the soil depth, including the surface layer, 1～10 cm,10～20 cm, 20～35 cm and 35～50 cm, except the cropland site only four layers. The soilsamples were collected in June, August and October in 2006, respectively. Determined soilorganic carbon and other soil nutrients, the soil microorganism composition and seasonchange, several kinds key soil enzymes which correlation with debase and solution(amylase, cellulose, saccharose, etc.) activity and season change and the soil activity organiccarbon composition distribute and regulation with dynamic state. The correlation analysiswas conducted by the SPSS software. The key results from these studies are summarized asfollows.1. The content of soil organic carbon, total nitrogen, total phosphorus and potassium ineach sample soil are affluent. The contents of all the physicochemical parameters weredecreased with the soil depth increasing. The contents in the surface layer soil are thehighest. The content of organic carbon is highest. Its distribution trend is primitive Abieafaxoniana＞45-year-old planted spruce forest＞25 year-old planted spruce forest＞cropland.2. The microorganism composition and seasonal changes in all the soil samples wereanalyzed by using the cultural methods..The result shows that the number of bacteria is the mostly component in each sample soil, then is the number of actinomyces and fungi leastand it is obviouly descend trend with soil depth increasing. Distributing trend in the fourkinds of soil: The number of bacteria in the originality Abiea faxoniana and fungi in thevegetable soil is most, actinomyces second. The season transformation trend: June＞August＞October. Soil enzyme (amylase, cellulose and saccharose) activity is descend with soildepth increasing. The originality Abiea faxoniana and cropland has highest and lowestenzyme activity. But amylase and cellulose enzyme activity have not more obvious seasonvariety and the saccharose enzyme activity don't obviously season change.3. The content variety trend of soil microbial biomass carbon, water dissolvedorganic carbon and labile organic carbon of each sample soil in the soil section is decreasingwith soil depth increasing.The content of these indexes in the cropland soil is the lowest.The content of soil microbial biomass carbon and water dissolved organic carbon in theprimitive Abiea faxoniana site is the tallest. The content of labile organic carbon in the45-year-old planted spruce forest site is the highest. The season change of soil microbialbiomass carbon content and labile organic carbon content are in August and Octorber morethan in June. The content of water dissolved organic carbon is the highest in August, andthen is in June and Octorber. The seasonal change of labile organic carbon content is inOctorber＞August＞June.4. The result of correlation analysis showed that the number of bacteria and fungi in theprimitive Abiea faxoniana, the number of bacteria and actinomyces in the 45-year-oldplanted spruce forest,the number of actinomyces in the cropland with every index isnotability or best notability relativity. The number of bacteria,fungi and actinomyces witheach index is basic positive relativity.
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