Effects of warming and nitrogen input on soil N2O emission from Qinghai-Tibetan Plateau: a synthesis

• Annual N 2 O emission is 0.73 kg N 2 O-N ha −1 on average from background soils over the Qinghai-Tibetan Plateau • Soil warming has a small negative effect on N 2 O emission from non-permafrost soils over the Qinghai-Tibetan Plateau • Warming-induced thawing may result in significant N 2 O emission in the permafrost but remains highly uncertain • Enhanced N input stimulates N 2 O emission over the Qinghai-Tibetan Plateau, with an overall small emission factor (< 1%) 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 N 2 O emission. So far, a number of studies have reported variabilities of N 2 O 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 N 2 O emission is still lacking for the QTP. Here, based on available studies published for this region, we investigated spatiotemporal patterns of background N 2 O fluxes and performed a meta-analysis to examine the warming and N-addition effects on N 2 O emission. Annual N 2 O fluxes ranged from -0.33 to 2.14 kg N 2 O-N ha −1 yr −1 (mean =0.73), of which their spatial distributions across ecosystems were mainly reflected by mean annual precipitation. N 2 O fluxes during growing seasons were generally larger than those in non-growing seasons, but hot moments of N 2 O emission existed during freeze-thawing periods. Our meta-analysis showed that warming had a significantly negative but minor effect on N 2 O emission from non-permafrost soils, although the effect varied with warming magnitudes and methods. The negative response of N 2 O 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 N 2 O emission. N addition exhibited an overall positive impact on N 2 O emission over the QTP region, with a moderate emission factor (0.8%) lower than the IPCC value. Considering the moderate N 2 O emission from background soils (< 1 kg N 2 O-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 N 2 O source in the near future.