Deepened snow cover alters biotic and abiotic controls on nitrogen loss during non-growing season in temperate grasslands

Despite the fact that winter lasts for a third of the year in the temperate grasslands, winter processes in these ecosystems have been inadequately represented in global climate change studies. While climate change increases the snow depth in the Mongolian Plateau, grasslands in this region are also simultaneously facing high pressure from land use changes, such as grazing, mowing, and agricultural cultivation. To elucidate how these changes affect the grasslands’ winter nitrogen (N) budget, we manipulated snow depth under different land use practices and conducted a 15 NH 4 15 NO 3 -labeling experiment. The change in 15 N recovery during winter time was assessed by measuring the 15 N/ 14 N ratio of root, litter, and soils (0–5 cm and 5–20 cm). Soil microbial biomass carbon and N as well as N 2 O emission were also measured. Compared with ambient snow, the deepened snow treatment reduced total 15 N recovery on average by 21.7% and 19.2% during the first and second winter, respectively. The decrease in 15 N recovery was primarily attributed to deepened snow increasing the soil temperature and thus microbial biomass. The higher microbial activity under deepened snow then subsequently resulted in higher gaseous N loss. The N 2 O emission under deepened snow (0.144 kg N ha −1 ) was 6.26 times than that of under ambient snow (0.023 kg N ha −1 ) during the period of snow cover and spring thaw. Although deepened snow reduced soil 15 N recovery, the surface soil N concentration remained unchanged after five years’ deepened snow treatment because deepened snow reduced soil N loss via wind erosion by 86%.