The Relative Influence Of Topographical Factors And Protective Mechanisms To The Accumulation Of Soil Organic Carbon In The Hilly Area Of Western Zhang Guang Cai Mountains

In the hilly area of western Zhang guang cai Mountains, a typical secondary forest region of northeast China, a total of 36 sampling plots were established symmetrically in accordance with the position and aspect of slope, and soil samples representing different genetic horizons were collected within a profile depth of 100cm. The number of soil organic carbon and organic carbon fractions were analysed. The effects of topographical factors (the position, aspect, and gradient of slope) on soil organic carbon (SOC) content and density were investigated, and the relations between SOC content and physical protection factors (clay, aggregate) were analysed. The physical protection and stability mechanism of soil organic carbon were revealed. Stepwise regression analysis was employed to quantify the relative influence of each factor. The results show that:The SOC density within lm profile ranged from 8.9～31.3kg/m2, of which 55.2% was concentrated in the A horizon on average. The spatial variability is great and the characteristic of tables together is obvious.SOC distribution was significantly influenced by slope position and aspect. Down-slope sites hold 83% more SOC in the A horizon and 67% more SOC in the lm profile than upslope sites, while ubac sites hold 37% more SOC in the A horizon and 17% more SOC in the lm profile than adret sites respectively. No significant relation was found between the amount of SOC and the gradient of slope, when the down-or upslope sites were examined alone.Though it yielded varied patterns when correlating SOC with clay or aggregate, no significant relation between SOC and any of the two physical protection factors could be ascertained if take out some statistical disturbances (i.e. slope position and buried horizon), which led us to the perverse recognition that clay and aggregate protection are controlling factors for SOC accumulation. Organic carbon fractions were analysed further, the same thing was proved.Stepwise regression analysis suggested that slope position was the dominating factor, which alone could explain 57.5% of the spatial variability of SOC density for the A horizon and 63.2% for the lm profile, while clay and aggregate were eliminated from the equation due to negligible contribution.The scientific basis is provided to study soil organic carbon physical protection and stability mechanism by the results. What’s more, the results of this study have implications for accurate estimation of SOC stock in hilly areas, and for site selection of carbon sink forests.