| In this paper, the forest soil which in mountain forest-the arid valley of ecotones in Li County in the upper Minjiang River was studied. Along the elevation gradient, we divide the study area into three parts:typical arid valley area, ecotones area and mountain forest area. In these three parts, we choose representation of vegetation types respectively, and carry out vegetation surveys and soil sampling analysis. Study the soil organic carbon variation in different conditions of vegetation and different environmental factors. Explore the mountain forest-the arid valley of ecotones vegetation restoration and management of the adjustment mechanism, and enrich Ecotones ecological theory of evolution, and ultimately to provide a theoretical basis in the mountain forest-the arid valley of ecotones vegetation restoration and management of complex ecosystems. The results indicated:(1) The amount of total organic carbon (TOC) is between 14.79g/Kg～51.61g/Kg. The amount of total organic carbon increased along the elevation gradient and decreased with the increasing soil depth.(2) The amount of microbial biomass carbon (MBC) is between 95.44-339.81mg/kg, the amount of water-solubable organic carbon (WSOC) is between 8.36-33.50mg/kg and the amount of particulate organic carbon (POC)is between 1.23-20.16g/kg. The amount of MBC, WSOC, POC are all increased along the elevation gradient and decreased with the increasing soil depth. The four kinds of organic carbon correlated positively with each other. The order of ratios of three type labile carbon to TOC was: POC/TOC>MBC/TOC>WSOC/TOC. The order of ratios of MBC to TOC is between 0.645%～0.937%. The order of ratios of WSOC to TOC is between 0.048%～0.092%. The order of ratios of POC to TOC is between 6.763%～20.563%.(3) Significant seasonal variation of soil labile organic carbon was found. The amount of MBC was high in summer and autumn low in winter and spring. The amount of WSOC was high in autumn and winter low in spring and summer. The dynamic of MBC and WSOC was largely affected by seasonal variation of temperature and soil moisture. In summer the temperature is high and this time is the rainy season, the amount of MBC is the maximum or the amount of WSOC is the minimum. So, seasonal variation of temperature and soil moisture is the important factor to the dynamic of MBC and WSOC.(4) The chemical and physical properties of soils varied along the elevation gradient. TN, soil moisture, silt, clay increased along the elevation gradient; pH value and sand grain decreased along the elevation gradient; TP, TK, soil bulk density increased and then decreased along the elevation gradient. Correlations between TOC, POC, WSOC, MBC with TN, TP, TK, pH value, soil moisture, sand grain, silt, clay and soil bulk density were analyzed. The results indicated that TOC, POC, WSOC, MBC correlated significantly positive with TN, TP, TK, soil moisture, and correlated significantly negative with pH value; no significant correlations were found between TOC, POC, WSOC, MBC with sand grain, silt,soil bulk density; no significant correlations were found between TOC, POC, MBC with clay, WSOC correlated positively with clay.(5)The amount of TOC, TN, TP, TK, soil moisture and clay in Mountain forest-ecotones area and plantation area are larger than that of the arid valley area shows that the natural conditions of the two areas are superior to the lower valley. So the vegetation can be recovery gradually as long as the afforestation suitably, closed forest measure and to reduce the disturbance of grazing. Therefore, in the process of vegetation restoration, the impact of elevation on the distribution of soil nutrients should be considered. Along ecotones, restoration forest from top to the bottom step by step and make the timberline downward gradually, and ultimately to achieve the restoration of vegetation in arid valley, is a well-established channel in arid valley vegetation restoration, can be carried out in the arid valley of the promotion of vegetation recovery.
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