Methane emissions in grazing systems in grassland regions of China: A synthesis

Abstract The effects of grazing on methane (CH 4 ) budgets are important for understanding the balance of greenhouse gas emissions and removals in grassland ecosystems. However, the CH 4 budgets of grazing systems, that is simultaneously considering CH 4 uptake by grassland soils and emissions from ruminant enteric fermentation, livestock folds and animal feces, are poorly investigated, particularly for Chinese grasslands, and thus, remained unclear currently. Here, a synthesis of 43 individual studies was carried out to assess the grazing season/annual CH 4 budgets and their responses to grazing in grassland ecosystems of China. The results showed that heavy grazing (HG) significantly decreased, while light grazing (LG) and moderate grazing (MG) had no significant effects soil CH 4 uptake, as compared to un-grazing sites. Grazing has shifted Chinese grasslands from a sink to source for atmospheric CH 4 , and the grazing season/annual CH 4 budgets increased with increasing grazing intensity, while the offset of CH 4 uptake by grassland soils to total CH 4 emissions from sheep, sheepfolds and feces were exponentially decreased with increasing grazing intensity. Moreover, the herbage biomass (HBM), organic matter intake (OMI) and live weight gain (LWG) were decreased while CH 4 emission intensities (i.e., CH 4 emission per HBM, OMI, and LWG) were linearly increased with increasing grazing intensity. Our results demonstrate that mediating grazing intensity, e.g., from HG to LG, could yield the optimal balance between maintaining productive grasslands and meanwhile mitigating CH 4 emissions. This study could help for building strategies with implications for grassland management in China with similar CH 4 emission problems.