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ABSTRACT:As one of the most sensitive regions to climate change, the Qinghai-Xizang Plateau has been widely investigated as one unity for impacts of climate change on alpine grassland. However, previous findings might be confounded by distinct climate sensitivities at different elevations and different regional climates between Qinghai Province and Xizang Province, which lie at the two sides of Tanggula Mountains. In this study, we explored change trends of grassland vegetation, temperature and precipitation in growing season from 1982 to 2011, and elevation-dependent effects of climate change on grassland vegetation in the two provinces separately. The plateau grassland greenness gained improvement under climate warming and wetting during the past 30 years, especially in Qinghai Province. Temperature increased significantly with a warming magnitude of more than 1.5 ∘ C over the plateau grassland. The interannual change of precipitation showed contrary trends between the two provinces. The main climate factor driving the grassland vegetation variation varied between the two provinces, with temperature being the main factor in Qinghai Province and precipitation being the main factor in Xizang Province. In particular, a more significant correlation between climate change and grassland vegetation variation was found at higher elevations, which reveals higher climate sensitivity in higher elevation areas of the plateau.

Anthropogenic methane emissions in China increased by 40% in the 2000s, contributing 16% of global anthropogenic emissions. The trend after 2010, however, remains under debate. An improved understanding of major sources and their trends, informed by timely and accurate data, is required to monitor efforts toward climate mitigation goals. Here we update a detailed bottom-up inventory to evaluate recent changes in China’s anthropogenic CH4 emissions. Combining our and other bottom-up inventories and seven global CH4 inversions, we show a slowdown of emission increase after 2010 [0.2 (−0.3 to 0.7) Tg of CH4 year–2] compared to the 2000s [1.2 (0.6–1.8) Tg of CH4 year–2], with a downward trend detected after 2014. Although there are considerable uncertainties, this slowdown is statistically significant (p < 0.001). The slowdown is mainly attributed to stabilized coal production in the 2010s, along with a regional shift of production toward mining areas with low emission factors and increased utilization of coal mine methane. Our results suggest that China’s recent energy policies have helped control coal mine emissions, and further work is needed to narrow down the uncertainty in both bottom-up inventories and top-down inversions.

The impacts of enhanced nitrogen (N) deposition on the global forest carbon (C) sink and other ecosystem services may depend on whether N is deposited in reduced (mainly as ammonium) or oxidized forms (mainly as nitrate) and the subsequent fate of each. However, the fates of the two key reactive N forms and their contributions to forest C sinks are unclear. Here, we analyze results from 13 ecosystem-scale paired 15N-labelling experiments in temperate, subtropical, and tropical forests. Results show that total ecosystem N retention is similar for ammonium and nitrate, but plants take up more labelled nitrate ($${20}_{15}^{25}$$ 20 15 25 %) ($${{{{{{\rm{mean}}}}}}}_{{{{{{\rm{minimum}}}}}}}^{{{{{{\rm{maximum}}}}}}}$$ mean minimum maximum ) than ammonium ($${12}_{8}^{16}$$ 12 8 16 %) while soils retain more ammonium ($${57}_{49}^{65}$$ 57 49 65 %) than nitrate ($${46}_{32}^{59}$$ 46 32 59 %). We estimate that the N deposition-induced C sink in forests in the 2010s  is $${0.72}_{0.49}^{0.96}$$ 0.72 0.49 0.96  Pg C yr−1, higher than previous estimates because of a larger role for oxidized N and greater rates of global N deposition.