Fluxes of nitrous oxide, methane and carbon dioxide during freezing-thawing cycles in an Inner Mongolian steppe

Fluxes of nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) were followed at winter-grazed (WG) and ungrazed steppe (UG99) in Inner Mongolia during the winter-spring transition of 2006. Mean fluxes during the period March 12-May 11 were 8.2+/-0.5 (UG99) and 1.5+/-0.2 mu g N2O-N m(-2) h(-1) (WG) for N2O, 7.2+/-0.2 (UG99) and 3.0+/-0.1 mg CO2-C m(-2) h(-1) (WG) for CO2 and -42.5+/-0.9 (UG99) and -14.1+/-0.3 mu g CH4-C m(-2) h(-1) (WG) for CH4. Our data show that N2O emissions from semi-arid steppe are strongly affected by freeze-thawing. N2O emissions reached values of up to 75 mu g N2O-N m(-2) h(-1) at the UG99 site, but were considerably lower at the WG site. The observed differences in N2O, CH4 and CO2 fluxes between the ungrazed and grazed sites were ascribed to the reduced plant biomass at the grazed site, and-most important-to a reduction in soil moisture, due to reduced snow capturing during winter. Thus, winter-grazing significantly reduced N2O emission but on the other hand also reduced the uptake of atmospheric CH4. To finally evaluate which of the both effects is most important for the non-CO2 greenhouse gas balance measurements covering an entire year are needed.