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

Abstract

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 μg 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 μg 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 μg 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.