Abstract Grazing can degrade grassland soil and increase nitrous oxide (N2O) emissions, but the underlying mechanism is poorly understood. We investigated the relationship of soil N2O emission with nitrifying enzyme activity (NEA), denitrifying enzyme activity (DEA), and the abundances of N2O-producing and N2O-reducing functional genes, in response to three grazing intensities (none, light, intensive) over two growing seasons on an alpine grassland on Kunlun Mountain in semi-arid North China. Compared to the non-grazed control, light and intensive grazing treatments increased the 2-yr total N2O emissions by 27.5% and 68.1%, respectively. Daily N2O flux rate correlated positively with soil water-filled pore space (WFPS), temperature, and dissolved organic carbon (DOC) but not with the abundances of nitrifiers (AOB, AOA, Nitrobacter-like nxrA), nitrate reducers (narG) and denitrifiers (nirS, nirK, and nosZ). These results suggest that soil environmental factors rather than nitrifier, N2O-producer and N2O-reducer abundances were more important in determining the grazing enhancement of N2O emissions from the alpine grassland in semi-arid areas. The abundance of AOB and Nitrobacter-like nxrA but not AOA correlated positively with NEA, indicating they are good indicators for the potential nitrification in this arid alpine grassland. Reducing grazing intensity from intensive to light resulted in more above-ground biomass and N uptake in both years and less N2O emissions in 2018. These results highlight the importance of establishing a proper grazing intensity to reduce N2O emissions from the degraded grassland while maintaining productivity for livestock.

中文翻译：

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放牧增加 N2O 排放与高寒草地土壤理化特性有关，与硝化菌和反硝化菌丰度无关

摘要 放牧可以使草地土壤退化并增加一氧化二氮（N2O）的排放，但其潜在机制尚不清楚。我们研究了土壤 N2O 排放与硝化酶活性 (NEA)、反硝化酶活性 (DEA) 以及产生 N2O 和减少 N2O 功能基因丰度的关系，以响应三种放牧强度（无、光、密集）华北半干旱地区昆仑山高寒草原两个生长季以上。与非放牧控制相比，轻度放牧和集约化放牧处理使 2 年 N2O 总排放量分别增加了 27.5% 和 68.1%。每日 N2O 通量率与土壤充水孔隙空间 (WFPS)、温度和溶解有机碳 (DOC) 呈正相关，但与硝化菌 (AOB、AOA、类硝化杆菌 nxrA) 的丰度无关，硝酸盐还原剂 (narG) 和反硝化剂（nirS、nirK 和 nosZ）。这些结果表明，土壤环境因素而不是硝化剂、N2O 生产者和 N2O 还原剂的丰度在决定半干旱地区高寒草地 N2O 排放的放牧增强方面更为重要。AOB 和 Nitrobacter-like nxrA 而不是 AOA 的丰度与 NEA 呈正相关，表明它们是该干旱高寒草原潜在硝化作用的良好指标。将放牧强度从集约减少到轻放导致两年内地上生物量和氮吸收量增加，2018 年 N2O 排放量减少。 这些结果强调了建立适当放牧强度以减少退化草地的 N2O 排放同时保持生产力的重要性家畜。