Temporal Variations in Soil CO2 Efflux Under Different Land Use Types in the Black Soil Zone of Northeast China

The quantification of soil CO2 efflux is crucial for better understanding the interactions between driving variables and C losses from black soils in Northeast China and for assessing the function of black soil as a net source or sink of atmospheric CO2 depending upon land use. This study investigated responses of soil CO2 efflux variability to soil temperature interactions with different soil moisture levels under various land use types including grassland, bare land, and arable (maize, soybean, and wheat) land in the black soil zone of Northeast China. The soil CO2 effluxes with and without live roots, defined as the total CO2 efflux (FtS) and the root-free CO2 efflux (FrfS), respectively, were measured from April 2009 to May 2010 using a static closed chamber technique with gas chromatography. The seasonal soil CO2 fluxes tended to increase from the beginning of the measurements until they peaked in summer and then declined afterwards. The mean seasonal FtS ranged from 20.3+/-7.8 to 58.1+/-21.3 mg CO2-C m(-2) h(-1) for all land use types and decreased in the order of soybean land > grassland > maize land > wheat land > bare land, while the corresponding values of FrfS were relatively lower, ranging from 20.3+/-7.8 to 42.3+/-21.3 mg CO2-C m(-2) h(-1). The annual cumulative FtS was in the range of 107-315 g CO2-C m(-2) across all land uses types. The seasonal CO2 effluxes were significantly (P < 0.001) sensitive to soil temperature at 10 cm depth and were responsible for up to 62% of the CO2 efflux variability. Correspondingly, the temperature coefficient Q(10) values varied from 2.1 to 4.5 for the seasonal FtS and 2.2 to 3.9 for the FrfS during the growing season. Soil temperature interacting with soil moisture accounted for a significant fraction of the CO2 flux variability for FtS (up to 61%) and FrfS (up to 67%) via a well-defined multiple regression model, indicating that temperature sensitivity of CO2 flux can be mediated by water availability, especially under water stress.