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Highlights • The effects of N deposition on global WUE were evaluated with IBIS model. • WUE changed in several N deposition hotspots owing to larger change in GPP than in ET. • N deposition has significantly increased the response ratio of WUE to elevated CO 2 in some regions. Abstract Nitrogen (N) deposition changes the availability of N in ecosystems and regulates carbon and water cycles, including ecosystem water use efficiency (WUE). In recent decades, N deposition has been increasing rapidly, especially at several hotspots in China, Europe and the U.S. In this study, a process-based terrestrial ecosystem model, IBIS (Integrated BIosphere Simulator), was used to simulate the effects of N deposition on WUE globally. The results indicated that increasing N deposition led to a global increase in WUE of 0.005 g C kg−1 H 2 O on average over the first 10 years of the 21st century. The effects of N deposition on WUE were more evident in certain hotspots than in other parts of the world. The effect of N deposition on gross primary productivity (GPP) determined the change in WUE. In particular, high N deposition led to decreased ET and consequently increased the WUE in southeastern China. Moreover, increased N deposition has significantly enhanced the WUE in response to elevated CO 2 in southeastern China, indicating the importance of N deposition in regulating the terrestrial carbon cycle. [ABSTRACT FROM AUTHOR]

Increased nitrogen (N) deposition and land-use and land-cover change (LUCC) have influenced the terrestrial ecosystem carbon budget in China over the past few decades. However, the coupling effects of N deposition and LUCC on the carbon cycle remain unclear. This study first evaluated the effects of LUCC on N deposition based on estimated N deposition data from NO column remote sensing data and the GlobeLand30 LUCC dataset, and then assessed the coupling effects of N deposition and LUCC on carbon budgets in China based on a terrestrial ecosystem process-based model. The results showed that the average rate of increase in N deposition in China was 0.35 Tg N yr (Tg = 10 g), which caused net primary production (NPP) and net ecosystem production (NEP) to rise by 92.2 Tg C yr and 46.9 Tg C yr, respectively. The effects of LUCC reduced N deposition by 0.21 Gg N yr (Gg = 10 g). The land changed from forest to cropland had the greatest rate of increase in N deposition among all types of land-cover change. Changes from cropland to forest slowed the rate of N deposition increase the most. Generally, the change in N deposition resulting from LUCC reduced NPP and NEP by 0.7 and 0.4 Gg C yr, respectively. Compared with the total effects of N deposition on NPP and NEP, N deposition changes caused by LUCC had a limited aggregate effect on the C budget. [ABSTRACT FROM AUTHOR]

China has the largest reactive nitrogen deposition worldwide. Understanding the change of nitrogen deposition and its socioeconomic drivers in China is crucial for the function and sustainability of regional and global ecosystems. Here we presented satellite-derived nitrogen deposition constrained with the national ground-based measurements over China. We found that oxidized nitrogen deposition peaked at 7.0 kg N ha−1 in 2012, then decreased to 6.2 kg N ha−1 in 2017. In contrast, reduced nitrogen deposition increased continuously, and reached 12.6 kg N ha−1 in 2017. The Chinese Clean Air Act is responsible for the reduction of oxidized nitrogen emissions, while there is no current effective control policy for ammonia emissions in place resulting in reduced nitrogen deposition reaching levels of approximately twice that of oxidized nitrogen in 2017. The ratio of reduced to oxidized nitrogen deposition decreased from 1.30 in 2008 to 1.08 in 2011, while this ratio began to increase from 1.08 in 2011 to 1.56 in 2017. This suggests reduced nitrogen deposition would become more important in the air quality and their ecological consequences in the future. The total nitrogen deposition in China was about 3–4 times that in the US and Europe. The policy of controlling nitrogen pollution is urgent, especially for reducing ammonia emissions, while ensuring the sustainable production of agriculture and maintaining food security. Image 1 • Methods were developed to obtain N deposition using satellite observations. • The ratio of reduced to oxidized N deposition in China increased since 2011. • N deposition in China was about 3–4 times that in the US and Europe. [ABSTRACT FROM AUTHOR]

• DNDC has the potential to assess the effect of N deposition on rice ecosystems. • The N deposition increased 0.6% national rice production. • 1.8% N deposition is used for rice growth; the remaining is in the surroundings. • The recommended fertilizer application can be basically for rice growth. The influence of enhanced nitrogen (N) deposition on rice ecosystems was evaluated across China using the DNDC (DeNitrification-DeComposition) model. The simulated grain, leaf, stem, root and total biomass had good consistency with the ground measurements in controlled experiments, with absolute relative errors of 4.5, 7.3, 7.7, 7.3 and 4.7%, respectively. On a national scale, the absolute relative errors of the measured and simulated early, late and single cropping rice was 2.2, 6.6 and 5.9%, respectively. The N deposition increased rice yield accounted for 0.6% of the national rice production. Under the current fertilization conditions, The N deposition was barely absorbed and utilized for rice growth (only accounted for 1.8% of the N deposition). About 57.7% of the N deposition remained in the soil as inorganic and organic forms, and the other 40.5% of the N deposition was emitted to the environment, as nitrogen oxide emissions (24.8%), ammonia volatilization (5.6%), leaching and runoff (10.1%). These results will provide scientific bases for recommending fertilizer rates and enacting policies to protect the eco-environment. [ABSTRACT FROM AUTHOR]