Effects Of Wetland Draine On Soil Carbon Fractions In Xiaoxing’an Mountains

Soil labile organic carbon as a part of soil organic carbon has a certain solubility and easy mineralization. The concentration of labile organic affected by plants and microbes in the soil. Athlough the proportion of labile carbon occupies a small part of soil organic carbon, it play important role in carbon cycling and it participates in lots of physical chemical and biological processes in soil. The dynamics of active carbon have great significance to the global ecosystem carbon cycle. Since the 1970 s, wetlands in Xiaoxing’an Mountains, which one of the main mountain wetland distribution areas in Northeast of China, have been drained to increase the growth potential of forest sites. When forest wetlands are drained, Soil thermometers and hydrology, soil oxidization-reduction processes was significantly changed and the change of the proportion of labile carbon will be accelerated. Large of cold forest swamps area are distributed in Xiaoxing’an Mountains. In this paper, selecting natural sedge swamps and artificial larch swamps of different time drainaged forestation in Xiaoxing’an Mountain as the objects, we studied the dynamics of labile carbon fractions in different depths and soil type to explore the affecting factors. We also revealed the influence of drainage forestation time on soil carbon fractions. In order to understand the role of labile carbon fractions in the wetland carbon cycle to provide scientific basis. The main conclusions were as followed:(1)Soil physical and chemical properties change after swamps drained. As the The ecomposition of soil organic matter accelerated and the effect of organic nitrogen and phosphate rock enhanced. In addition, nutrient content decreases gradually with the fixed number of year of drainage increasing. The content of DOC and MBC reduced and the trend of vertical direction change after drainage, but there existed the obvious seasonal variation in the content of DOC and MBC before and after drainage and the trend of change is consist.(2)Decline rate of soil light fraction organic C(LFOC) was significantly higher than total organic carbon(TOC) and soil heavy fraction organic C(HFOC). After swamps drained, the proportion of LFOC decreased from 30% to 5% after forty years’ drainage. The allocation proportion of HFOC significantly increased with the time of drainage increasing, whereas LFOC dramatically declined. The original roots layer and litter layer suffered completely destruction and the important reason why the content of LFOC reduced quickly was the reduction of the litter supply and rapid decomposition of LFOC(3)After swamps has drained for 11 years, the upper content of dissolved organic carbon(DOC) decreased from 395±25 mg/kg to 280±25mg/kg, falling by 29%, falling by 46% after 22 years, thus a relatively stable value, that is, 195-212 mg/kg. As the growth of the drainage time, the value of DOC/TOC increased slowly. Long-term drainage led to the increase of the distributive proportion of the content of dissolved organic carbon in soil organic carbon, which caused the loss of soil organic carbon easily. The impact on the content of dissolved organic carbon in soil swamps drained had mainly occured in the surface layer(0-20cm). And the content of dissolved organic carbon in deep layer(20-40cm) changed a little because of swamps drained. The amount of existed organic carbon in soil and organic carbon returning to the soil was the main factor to determine the soil the number and the constitution of dissolved organic carbon in the soil.(4)The declining rate of total organic carbon in the soil was smaller than the soil microbial biomass carbon in the soil, and microbial quotient was diminishing gradually. After swmaps drained, Value of soil microbial biomass carbon in the soil was the highest in sedge swamp and it remained a relatively stable value in 2.7-2.9% with the increase of fixed number of year of the drainage. Organic carbon in the soil suffered a great loss and its availability decreased sharply, the effective efficiency of utilization of microorganism to carbon source decreased.The reduction of litter layer caused by the destruction of roots layer and the rapid decomposition active carbon fractions owing to the change of soil physical and chemical properties were the important reason for the quick drop of active organic carbon. LFOC, DOC, and MBC for different active carbon pools respectively and there existed close relationships among these three types of organic carbon fraction.Not only did the change of active organic carbon fraction indicate that swamps drained caused massive losses, but also the structure of component of organic carbon changed greatly and the availability of organic carbon declined immensely.