The influence of succession stages and climate on soil organic carbon density of broad-leaved Korean pine forest.

Broad-leaved Korean pine (Pinus koraiensis) forest and its secondary forests are important forest carbon sinks in northeast China and store a large amount of organic carbon in the soil. In this study we measured soil organic carbon density (SOCD) for different succession stages of Broad-leaved Korean pine forest at four typical sites (Changbai Mountain, Jiaohe, Wuying and Shengshan). We analysed total SOCD (0-60 cm), SOCD at the depth of 0-20 cm (topsoil) and the ratio of topsoil to total SOCD (top/total ratio) in relation to abiotic and biotic factors. The results showed that total and topsoil SOCD, and top/total ratio, changed differently with forest succession in different sites. Total SOCD was not related to latitude and three key climatic indices: mean temperature of the coldest month (MTCM), annual precipitation (AP), and warmth index (WI), while topsoil SOCD and top/total ratio were negatively related to latitude and positively related to MTCM. Multivariate analyses showed that total SOCD was less affected by climate than topsoil SOCD. Succession stage itself was not significant in explaining the SOCD variables, but the interaction of succession stage with temperature indices (MTCM and WI) showed a significant role for total SOCD and top/total SOCD ratio. In addition, total and topsoil SOCD were also significantly affected by slope position. Our results showed that topsoil SOCD was affected by climate and local topography. Total SOCD, however, is affected by a number of factors together. In addition to the weak direct effect of climate, community structure (lifeform and stand volume), local topography and the interaction of climate with succession stage also showed a significant effect on total SOCD.