Grassland Department of Animal Science and Technology College, China Agricultural University, No. 2 Yuanmingyuan West Road, Haidian District, Beijing 100193, China; Department of Ecology, School of Ecology and Environment, Inner Mongolia University, No. 235 West College Road, 010021, Hohhot, China.
State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry (LAPC), Institute of Atmospheric Physics, Chinese Academy of Sciences (IAP-CAS), Beijing 100029, China.
Sci Total Environ. 2019 Mar 1;654:662-670. doi: 10.1016/j.scitotenv.2018.11.102. Epub 2018 Nov 8.
The effects of grazing on methane (CH) budgets are important for understanding the balance of greenhouse gas emissions and removals in grassland ecosystems. However, the CH budgets of grazing systems, that is simultaneously considering CH 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 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 uptake, as compared to un-grazing sites. Grazing has shifted Chinese grasslands from a sink to source for atmospheric CH, and the grazing season/annual CH budgets increased with increasing grazing intensity, while the offset of CH uptake by grassland soils to total CH 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 emission intensities (i.e., CH 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 emissions. This study could help for building strategies with implications for grassland management in China with similar CH emission problems.
放牧对甲烷（CH）收支的影响对于理解草原生态系统中温室气体排放和清除的平衡非常重要。然而，放牧系统的 CH 收支（同时考虑草原土壤对 CH 的吸收以及反刍动物肠道发酵、牲畜畜栏和动物粪便的排放）研究甚少，特别是对于中国草原，因此目前仍不清楚。在这里，我们对 43 项单独的研究进行了综合分析，以评估中国草原生态系统中放牧季节/年 CH 收支及其对放牧的响应。结果表明，重度放牧（HG）显著降低了土壤 CH 吸收，而轻度放牧（LG）和中度放牧（MG）与未放牧的地点相比没有显著影响。放牧使中国草原从大气 CH 的汇转变为源，放牧季节/年 CH 收支随着放牧强度的增加而增加，而草原土壤对绵羊、羊圈和粪便总 CH 排放的吸收与 CH 排放量的抵消随着放牧强度的增加呈指数下降。此外，随着放牧强度的增加，牧草生物量（HBM）、有机物摄入量（OMI）和活体重增加（LWG）减少，而 CH 排放强度（即 HBM、OMI 和 LWG 每单位的 CH 排放）呈线性增加。我们的结果表明，调节放牧强度，例如从 HG 到 LG，可以在维持生产力高的草原和同时减轻 CH 排放之间取得最佳平衡。本研究有助于为中国类似 CH 排放问题的草原管理制定具有启示意义的策略。
