Responses Of Soil Organic Carbon Along Northeast China Transect To Environmental Changes

Soil organic carbon (SOC) is an important component of the global carbon cycle, and it has direct effects on the global carbon balance. In this paper, the spatial distribution of soil organic carbon and active carbon along NECT and their controlling factors were analyzed based on data from field survey along Northeast China Transect (NECT); Moreover, their responses to environmental changes were discussed by means of the simulated experiment under doubled CO2 and different soil water stresses. The main results were listed as follows:1. Along NECT, the mean contents of the soil organic carbon in soil A, B layer are 26.541±3.764 g. kg-1 and 11.108±2.559g .kg-1 respectively, and the mean contents of soil active carbon (SAC) are 4.312±0.726 g. kg-1 in soil A layer and 1.465±0.464 g . kg-1 in soil B layer. SAC was significantly related to SOC (R=0.976, P<0.01,n=86).2.The contents of SOC and SAC decreased fluctuating from east to west. Both of them were related prominently to mean annual precipitation (MAP), and pH, cation exchange capacity (CEC) and the silt content of soil (P<0.01). The relationships of SOC and SAC with precipitation were closer in soil A layer than those in soil B layer.3.Stepwise regression models of SOC and SAC in soil A layer, including MAP, pH, and CEC as factors, were developed (R=0.837 and R=0.896,P<0.05) respectively; while the models for soil B layer, including CEC and MAP as factors, were also developed (R=0.634 and R=0.607 ,P<0.05) respectively.4. In terms of the short-term simulated experiment, SAC did respond to environmental changes, but SOC didn't. Under different soil moisture conditions, the content of SAC is highest when soil moisture is between 45%~60% of soil water holding capacity; Under doubled CO2 conditions, the content of SAC increased when soil moisture is between 60%~80% of soil water holding capacity, but it decreased when soil moisture is below 60% of soil water holding capacity. Moreover, when different plants were grown in the experiment, the responses of SAC to environmental changes were different.