Moderate grazing reduces while mowing increases greenhouse gas emissions from a steppe grassland: Key modulating function played by plant standing biomass

Grassland represents one of the most expansive terrestrial ecosystems, exerting a profound influence on atmospheric greenhouse gas (GHG) levels within the broader context of global change. Both climate and land use changes play important roles in modulating grassland GHG emissions by directly or indirectly altering soil physical and chemical properties, especially soil temperature and inorganic nitrogen content. The optimal grassland management practices need to simultaneously meet the requirements of reducing GHG emissions, maintaining biological biodiversity, and ensuring productivity. However, the information on the management effects on GHG emissions from natural grasslands is still insufficient. Here we conducted a six-year grazing and mowing experiment in a semi-arid steppe grassland in central Inner Mongolia, and employed the static chamber method to investigate the effects of three major management measures, fencing, grazing and mowing, on ecosystem respiration (CO₂ emission), methane uptake (CH₄), and nitrous oxide emission (N₂O) patterns in the experimental grassland. The results demonstrated that: (i) moderate grazing reduced plant aboveground standing biomass and CO₂ emissions, but promoted belowground nutrient cycling and CH₄ uptake; (ii) mowing enhanced plant biomass production, increased soil carbon and nitrogen content, and also increased CO₂ emission; (iii) reducing grazing frequency reduced plant biomass loss and N₂O emissions. We conclude that grazing at a moderate intensity and frequency is the best for mitigating GHG emissions while maintaining grassland production, and that mowing enhancement of plant production and GHG emissions should be considered in optimizing grassland management.