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Annual atmospheric nitrogen (N) deposition in China increased approximately 8 kg N ha−1 from the 1980s to the 2000s, which may have greatly affected soil respiration (R s) and its temperature sensitivity (Q 10). Although numerous individual studies have been conducted, the responses of R s to simulated N deposition remain controversial. To reconcile the conflicting results of R s and expand our knowledge about the response of Q 10 to N addition, a dataset with 333 independent observations in China was compiled, and a meta-analysis was performed. Our results showed that N addition increased R s by 7.1% (P < 0.05) across all biomes. The positive response degree of R s in croplands (27.0%, P < 0.05) was significantly greater than those in the grassland and forest biomes, which indicated that R s in anthropogenic ecosystems might be more sensitive to N enrichment. In contrast to low and medium N levels (≤20 g m−2 yr−1), high N addition levels (>20 g m−2 yr−1) inhibited R s due to a decrease in plant fine root biomass (RB). Compared with ammonium nitrate, urea is more likely to stimulate the release of soil C. Regression models showed that the R s response ratio (RR) was positively correlated with pH and the RR s of microbial biomass carbon (MBC) and RB. Increases in both plant roots and microbial biomass induced by N addition directly promoted R s , and N enrichment likely increases R s in soil with a high pH. The temperature sensitivity parameter, Q 10 , decreased by 3.7% (P < 0.05) across all biomes and showed an overall negative response for different biomes (except wetlands and deserts), N addition levels and N types. The Q 10 response ratio was positively correlated with the RR of pH. Soil acidification induced by proton release during N fertilizer transformation might accelerate the decomposition of recalcitrant organic matter and further decrease the Q 10 value. Our study provides valuable information to Chinese environmental policy- and decision-makers in their attempts to evaluate the effects of N deposition on terrestrial ecosystem C cycle. • N addition increased R s by 7.1% and decreased Q 10 by 3.7% across all biomes. • Relative to grassland and forest, R s of cropland was more sensitive to N addition. • Contrary to low and medium N addition levels, high N addition levels inhibited R s. • Soil acidification induced by N addition increased R s and decreased the Q 10 value. [ABSTRACT FROM AUTHOR]

In China, sloping farmland accounts for one-third of its total farmland, supporting ~330 million mountain people's livelihoods. Despite its long history of using soil conservation measures for reducing soil loss on sloping farmland, no comprehensive evaluation has ever been performed on their effectiveness. In this study, we reviewed the soil conservation measures on sloping farmland in China from ~2500 years ago to the present and examined their effectiveness under current and projected climate change scenarios based on 6909 plot-scale observations. For the sloping farmland across China, the average soil loss rate is 14.47 Mg ha−1 yr−1, with a quarter of the observed values exceeding the maximum tolerable soil loss rate (10 Mg ha−1 yr−1). Soil conservation measures can reduce soil loss by ~80%, with the highest effectiveness for the combination of biological and engineering measures (reduced by ~86%), followed by biological measures (reduced by ~84%) and engineering measures (reduced by ~82%) separately. However, the effectiveness of soil conservation measures shows a significant decrease in the farmland with a slope above 15° or a single rainfall event >25 mm. The effectiveness of currently applied soil conservation measures was also compared under the Shared Socioeconomic Pathways (SSP) 1, 2, and 5 in 2050, and their effectiveness is expected to decrease on over 27% of the sloping farmland. In particular, under the SSP1 scenario, the effectiveness of soil conservation measures is projected to diminish in 70%, 54%, and 54% of sloping farmland in Northeast China, Sichuan Basin and surrounding regions, and Yunnan-Guizhou Plateau, respectively, due to changes in rainfall, highlighting the need to consider the impact of climate change when implementing soil conservation measures. Overall, this study provides useful information for scientific strategies on the construction, management, and maintenance of soil conservation measures to control soil loss on sloping farmland. [ABSTRACT FROM AUTHOR]