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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]

[Display omitted] • V cmax25 , N a and Chl a of winter wheat and paddy rice exhibited distinguishable seasonality. • The seasonality of leaf N a and Chl a were inconsistent with that of V cmax25. • Differentiating pre- and post-flowering stages significantly improved the estimation of V cmax25 from Chl a. Accurate representation of photosynthetic capacity and its seasonal variations is critical for modeling carbon sequestration of cropland ecosystems through photosynthesis. Previous studies indicated that the maximum carboxylation rate at 25 °C (V cmax25) is the key determinant of photosynthetic capacity and can be mapped according to leaf nitrogen (N) and chlorophyll (Chl) contents. However, whether relationships of V cmax25 with leaf nitrogen and chlorophyll contents in cropland ecosystems change over the whole growing season remain unclear. To address this question, we conducted intensive field campaigns in winter wheat and paddy rice farmlands of Eastern China, with leaf V cmax25 , the maximum electron transport rate at 25 °C (J max25), N, and Chl measured every 7 to 10 days from the tillering stage to maturity. Results showed that V cmax25 and J max25 varied significantly during the growing seasons and maximized at flowering stages. For both winter wheat and paddy rice, Chl a (Chl content at the area unit) showed significantly different relationships with V cmax25 pre- and post- flowering while N a (N content at the area unit) did not. When different empirical models were used for pre- flowering and post- flowering stages, V cmax25 estimated from Chl a was closer to observations (R2 = 0.875, RMSE = 9.479 µmol m−2 s−1) than that estimated from N a (R2 = 0.565, RMSE = 17.718 µmol m−2 s−1). The findings in this study imply that the combination of remotely sensed leaf Chl a content and phenology would improve the mapping of V cmax25 for crops at regional and even global scales. [ABSTRACT FROM AUTHOR]

Atmospheric methane (CH4) is an important greenhouse gas that can reflect variations of CH4 emissions and sinks. This study aimed to detect spatial and temporal variations of atmospheric CH4 concentrations in China during 2003–2021 based on CH4 column-averaged dry-air mole fraction (XCH4) products from three satellites, namely, Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY), Greenhouse Gases Observing Satellite (GOSAT), and Copernicus Sentinel-5 Precursor (S5P). The results revealed that XCH4 observed from three satellites showed high agreement in spatiotemporal variations and demonstrated good consistency with ground station measurements. The correlation coefficients (r) between the three satellites were 0.72 and 0.73, and the correlation coefficients for the ground stations were 0.79, 0.66, 0.03, 0.21, 0.70, and 0.80. The spatial distribution of XCH4 in China was generally high in the east and low in the west and close to that of CH4 emissions, indicating that CH4 emission sources dominated the spatial variations of atmospheric XCH4. From 2003 to 2006, XCH4 remained stable with an annual growth rate of 0.51 ppb·yr−1 and then abruptly increased with an overall growth rate of 6.96 ppb·yr−1. There were obvious seasonal changes in XCH4, with peaks in autumn and summer and nadir in winter and spring. These seasonal variations of XCH4 were related to CH4 emissions from rice planting. Rice cultivation areas generally had high XCH4 concentrations, and the growth cycle of rice plants significantly contributed to seasonal variations of XCH4 in the main rice planting areas. These results provide scientific data that could encourage decision-makers to enact policies and processes to reduce methane emissions. [ABSTRACT FROM AUTHOR]

A systematic dataset of an observation network on a national scale has been organized to investigate the spatial distribution of bulk sulfur (S) deposition (S dep ) throughout China during 2000–2013, representing by far the most detailed data set to track the bulk sulfur deposition throughout China since 2000. Such a dataset is needed for ecosystem studies and for developing emission control policies. Bulk S dep values showed great variations, ranging from 2.17 to 70.55 kg ha −1 y −1 , with an average of 22.99 kg ha −1 y −1 . The average rate of bulk S dep located in East Coastal region (35.97 kg ha −1 y −1 ), Middle Yangtze region (57.90 kg ha −1 y −1 ), Middle Yellow River region (23.42 kg ha −1 y −1 ), North Coastal region (42.19 kg ha −1 y −1 ), Northeast region (34.28 kg ha −1 y −1 ), South Coastal region (36.97 kg S ha −1 y −1 ), Southwest region (33.85 kg ha −1 y −1 ) was 4.50, 7.24, 2.93, 5.28, 4.29, 4.63 and 4.24 times than that in Northwest region (7.99 kg ha −1 y −1 ). Bulk S dep over China was mainly from fossil fuel combustion (76.96%), biomass burning (7.64%), crust (6.22%), aged sea salt (5.48%) and agriculture (3.68%). A systematic observation network on a national scale should be established to conduct a long-term monitoring atmospheric S dep (including wet and dry deposition), based on exiting ecological stations administrated by different departments in China. [ABSTRACT FROM AUTHOR]

Atmospheric nitrogen (N) deposition (Ndep), an important component of the global N cycle, has increased sharply in recent decades in China. Although there were already some studies on Ndep on a national scale, there were some gaps on the magnitude and the spatial patterns of Ndep. In this study, a national-scale Ndep pattern was constructed based on 139 published papers from 2003 to 2014 and the effects of precipitation (P), energy consumption (E) and N fertilizer use (FN) on spatial patterns of Ndep were analyzed. The wet deposition flux of NH4+-N, NO3--N and total Ndep was 6.83, 5.35 and 12.18 kg ha-1 a-1, respectively. Ndep exhibited a decreasing gradient from southeast to northwest of China. Through accuracy assessment of the spatial Ndep distribution and comparisons with other studies, the spatial Ndep distribution by Lu and Tian and this study both gained high accuracy. A strong exponential function was found between P and Ndep, FN and Ndep and E and Ndep, and P and FN had higher contribution than E on the spatial variation of Ndep. Fossil fuel combustion was the main contributor for NO3--N (86.0%) and biomass burning contributed 5.4% on the deposition of NO3--N. The ion of NH4+ was mainly from agricultural activities (85.9%) and fossil fuel combustion (6.0%). Overall, Ndep in China might be considerably affected by the high emissions of NOx and NH3 from fossil fuel combustion and agricultural activities. [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]