Significant changes in climate and perturbation from human activities have been reported over the Qinghai -Tibetan Plateau (QTP), likely altering the ecosystem nitrogen (N) cycling and thus N2O emission. So far, a number of studies have reported variabilities of N2O fluxes from background soil conditions, or conducted warming and N addition experiments to test these effects; however, a synthesized understanding of warming and N input on soil N2O emission is still lacking for the QTP. Here, based on available studies published for this region, we investigated spatiotemporal patterns of background N2O fluxes and performed a meta-analysis to examine the warming and N-addition effects on N2O emission. Annual N2O fluxes ranged from-0.33 to 2.14 kg N2O-N ha(-1) yr(-1) (mean =0.73), of which their spatial distributions across ecosystems were mainly reflected by mean annual precipitation. N2O fluxes during growing seasons were generally larger than those in non-growing seasons, but hot moments of N2O emission existed during freeze-thawing periods. Our meta-analysis showed that warming had a significantly negative but minor effect on N2O emission from non-permafrost soils, although the effect varied with warming magnitudes and methods. The negative response of N2O flux to warming could be explained by the associated decrease of soil moisture and enhancement of plant N uptake. In contrast, warming-induced thawing increases soil moisture in permafrost soils, which could stimulate N2O emission. N addition exhibited an overall positive impact on N2O emission over the QTP region, with a moderate emission factor (0.8%) lower than the IPCC value. Considering the moderate N2O emission from background soils (< 1 kg N2O-N ha(-1) yr(-1)) and common N limitation across ecosystems, our findings suggest that climate change and enhanced N inputs may not turn the QTP into a globally significant N2O source in the near future.

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/N-14 ratio of root, litter, and soils (0-5 cm and 5-20 cm). Soil microbial biomass carbon and N as well as N2O 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 N2O 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%.

Permafrost thawing may lead to the release of carbon and nitrogen in high-latitude regions of the Northern Hemisphere, mainly in the form of greenhouse gases. Our research aims to reveal the effects of permafrost thawing on CH4 and N2O emissions from peatlands in Xiaoxing'an Mountains, Northeast China. During four growing seasons (2011-2014), in situ CH4 and N2O emissions were monitored from peatland under permafrost no-thawing, mild-thawing, and severe-thawing conditions in the middle of the Xiaoxing'an Mountains by a static-chamber method. Average CH4 emissions in the severe-thawing site were 55-fold higher than those in the no-thawing site. The seasonal variation of CH4 emission became more aggravated with the intensification of permafrost thawing, in which the emission peaks became larger and the absorption decreased to zero. The increased CH4 emissions were caused by the expansion of the thawing layer and the subsequent increases in soil temperature, water table, and shifts of plant communities. However, N2O emissions did not change with thawing. Permafrost thawing increased CH4 emissions but did not impact N2O emissions in peatlands in the Xiaoxing'an Mountains. Increased CH4 emissions from peatlands in this region may amplify global warming.