Search

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. [ABSTRACT FROM AUTHOR]

Abstract: High N2O emissions have been observed in semi-arid grasslands, especially during freeze/thaw periods, when denitrification might be the main process of N2O production. However, there have been few denitrification studies in semi-arid grassland. This study was designed to determine the denitrification potential of four representative land cover types (typical steppe, meadow steppe, marshland, arid steppe) in two grasslands in Inner Mongolia, China. We found that soils from different land cover types exhibited significantly different denitrification potentials, with highest rates in marshland and lowest rates in arid steppe. Denitrification potentials were maximal in the upper layer and generally decreased with depth for all soils. Soil water content, soil carbon and nitrogen availability, and C/N ratio were found to be significantly correlated with denitrification potentials in all soils. Addition of glucose or/and nitrate significantly increased denitrification activities throughout the profile for all soils, suggesting that both bioavailable carbon and nitrogen were limiting factors of denitrification in these grasslands soils. However, further field studies are needed to translate the denitrification potentials determined in laboratory measurements to denitrification rates under field conditions. [Copyright &y& Elsevier]