Study On Characteristics Of Soil Labile Organic Carbon In Main Forest Types In The North Of Daxing’ Anling Mountains

Soil organic carbon was an important component of soil nutrients. The accumulation and decomposition of it had a direct impact on the global carbon balance. But its short-term changes are difficult to observe. The soil labile organic carbon can reflect the small changes of soil which was caused by management practices and environmental changes before the soil organic carbon changes, and it can be used as early indicators of the changing of soil organic carbon. To reveal the characteristics of soil labile organic carbon content in different forest types, we chosen the 0-32 cm soil layer of 5 forest types in north of Daxing’an mountains to sample soil from June to October of 2014.The 5 forests types are birch forest dominated by Betula platyphylla, poplar forest dominated by Populus davidiana, larch forest dominated by Larix gmelinii, mongolian pine forest dominated by Pinus sylvestnis var. Mongolica and poplar-birch forest dominated by Populus davidiana and Betula platyphylla. We measured the contents of microbial biomass carbon(MBC), dissolved organic carbon(DOC), readily oxidizable carbon (ROC), particulate organic carbon (POC), physical and chemical properties, and enzymatic activity of soils in 5 forest types and analyzed their correlations with each other. The results shows that the content of MBC and DOC in different soil layer varied from 220.40 mg/kg to 909.54 mg/kg, and from 64.71 mg/kg to 99.05 mg/kg, respectively, and the content of ROC and POC in different soil layer varied from 1.89 g/kg to 15.89 g/kg, and from 5.78 g/kg to 59.73 g/kg, respectively. The contens of soil labile organic carbon significantly differed between 5 forest types, which were higher in broadleaved forests than in coniferous forests in MBC, ROC and POC. Soil labile organic carbon contents of 5 forest types had obvious seasonal fluctuations. The soil MBC contents showed a characteristic that it was low in summer and high in winter. The soil ROC contents generally showed wavely increasing trend.The content of DOC and POC showed different changing trend with the changes of seasons in different forest types, which had significantly different between different soil layer. In 5 forest types, the contents of soil labile organic carbon all decreased with increasing soil depth. The ratios of MBC to TOC, DOC to TOC, ROC to TOC and POC to TOC varied in the range 0.21% to 14.57%,0.03% to 1.00%,8.25% to 25.71% and 22.01% to 85.39%, respectively, and showed the trend that POC> ROC> MBC >DOC. There were significant correlations (P<0.01) between the activities of soil invertase, urease and alkaline phosphatase, soil total carbon content and soil labile organic carbon content, while the correlation between soil pH and soil labile organic carbon was not significant. The fitting equation of soil enzyme and total organic carbon to soil labile organic carbon reached a very significant level, which can consider that soil enzyme and total organic carbon can be the important indicators to evaluate the changes of soil labile organic carbon.