Spatial Variability of CO2, CH4, and N2O Fluxes during Midsummer in the Steppe of Northern China

Spatial variability is a major source of uncertainty in estimating the fluxes of greenhouse gases between steppe and atmosphere. The fluxes of CO2, CH4, and N2O were carried out between 08:00 and 10:00 h. of the following day during the midsummer period from a transect (area: 5.25×10 ha) in the semiarid steppe of northern China, using the dark static chamber technique and gas chromatography. Two land uses were chosen for this study: soils with plant covers and bare soils. Daily average GHG fluxes from the steppe transect were: 1.3×10 t C for CO2, -66.3 t C for CH4, and 1.1 t N for N2O. The emission of CO2 from soils with plant cover was significantly higher (P < 0.05) than that from the corresponding bare soils. The canopy effect, however, was observed for neither CH4 (P = 0.058) nor N2O (P = 0.772). Air temperature and relative humidity were the major factors affecting the diurnal variation in site-based CO2 flux (P < 0.05), while soil pH controlled its spatial variation (P < 0.05). The spatial uptake of CH4 correlated negatively with soil total N (TN) content (P < 0.05), while the flux of N2O significantly increased with soil organic carbon (P = 0.031) and TN (P = 0.022), indicating that soil organic matter is an important factor determining the N2O flux in the steppe