Methane and Nitrous Oxide Fluxes with Different Land Uses in the Temperate Meadow Steppe of Inner Mongolia, China

Abstract

Background and aims: Grazing and mowing are widely adopted management practices for the semiarid steppe in China that profoundly affect the greenhouse gas (GHG) flux in grassland ecosystems. However, the general mechanisms for CH4 and N2O fluxes in response to grazing and mowing remain poorly understood. Thus, we conducted year-round flux measurements of CH4 and N2O fluxes to investigate the effect of grazing and mowing on CH4 and N2O fluxes. Methods: Using manual static chamber and gas chromatography, we measured the fluxes of CH4 and N2O from grazing-exclusion, grazing and mowing sites from June 2019 to June 2020 in the Hulunbuir Grassland, Inner Mongolia. Results: Grazing and mowing increased soil temperature and reduced soil water content and soil inorganic N content. Compared with grazing and mowing, lower mean CH4 uptake (−67.58 ± 8.9 μg m−2 h−1) and higher mean N2O emissions (29.17 ± 6.8 μg m−2 h−1) were found at the grazing-exclusion site. No pulse emissions of N2O were found for all sites during the spring thaw period (STP), and only two small N2O emission peaks due to soil thawing were captured on April 2nd and 5th. The contribution of the spring thaw to the total annual N2O budget was small and accounted for only 10%, 13% and 12% of the annual fluxes at the grazing-exclusion, grazing and mowing sites, respectively. Conclusion: Our results indicate that grazing and mowing enhance CH4 uptake and inhibit N2O emissions, primarily due to the increased soil temperature and reduced soil water content and soil inorganic N content. No apparent pulse N2O emissions were observed at any of the three sites during the STP in the Hulunbuir grassland.