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Human activities have released a large amount of nitric oxides (NOx) into the atmosphere, leading to elevated regional atmospheric NOx concentration and nitrogen (N) deposition. Several studies have observed a downward NOx or NOy (NOx and its oxidation products) flux to the forest canopy, but attributed it to the photochemical reactions and conversion from gaseous N to particulate N. Here, we focus on the possibility of NOx sink by forest canopy based on an observed downward NOx flux of 0.28 kg N ha−1 yr−1 in a temperate forest of northeastern China, using hourly monitoring of NOx fluxes. In combination with results from previous studies, we find that the downward NOx or NOy fluxes ranged from 0.2 to 1.4 kg N ha−1 yr−1 in temperate forests and from 5.3 to 8.5 kg N ha−1 yr−1 in subtropical forests and they were positively related to atmospheric NOx concentration, mean annual air temperature and annual precipitation across eight forest sites from around the world. If assuming 50% of downward NOx or NOy was directly taken up by the canopy, we estimate a NOx or NOy sink of 0.2 and 1.1 Tg N yr−1 by global respective temperate and subtropical forests, representing an effective scavenger of atmospheric NOx and a considerable N source to forests. We suggest that interception of NOx or NOy by forest canopy should be considered in global NOx budgets and their contribution to the global forest N pool in global Earth System's models. Plain Language Summary: Canopy interception of reactive N has gained wide attention in recent several years, however, its quantification is still unclear. In the present work, we demonstrate the NOx downward movement in a typical temperate forest in northeastern China was partially driven by canopy biological uptake, and then combined results of our in situ observation of canopy NOx flux with other existing 10 monitoring sites worldwide. We estimated an N input of 0.2 and 1.1 Tg N yr−1 in global respective temperate and subtropical forests via downward NOx movement, representing an effective scavenger of atmospheric NOx and a considerable N source to forests. Key Points: The potential importance of canopy NOx uptake by forests for atmospheric NOx concentration and forest N pools is unclearCombining present and previous study results, we estimated a canopy N input of 0.2–1.1 Tg yr−1 in global temperate and subtropical forestsWe suggest that interception of NOx by forest canopy should be considered in global NOx budgets and forest N pools [ABSTRACT FROM AUTHOR]

Forests worldwide store large quantities of carbon (C), particularly in soils as soil organic C (SOC). In northeastern China, two dominant forest types, secondary mixed forest (MF) and larch plantation forest (LF), cover extensive areas. However, we lack an understanding of the patterns and the mechanisms of SOC storage and stabilization in MF and LF, especially in deep soil layers. This research aims to illustrate the vertical distribution and mineral protection of SOC over soil depth; we also used δ13C values of soil fractions to evaluate SOC stability. Samples from the surface litter (Oi), organic layer (Oa+e), and 0–40 cm mineral soils were collected from both MF and LF plots. We used two different methods to separate bulk soils into distinguished fractions: (1) macro- and micro-aggregates and the non-aggregated fraction, and (2) particulate organic matter (POM) and mineral-associated organic matter (MAOM). The C concentrations, C stocks, and δ13C of all soil fractions were determined. Our findings were as follows: (1) SOC was mainly stored in mineral soils and was 13.6% lower in LF (8609 ± 1180 g C m−2) than MF (9969 ± 2084 g C m−2). (2) In both MF and LF, the SOC stock was mainly stored in aggregates (averaged 92.7%); macroaggregates dominated in the surface layers (Oa+e layer and 0–10 cm) but microaggregates dominated in the deep layers (10–20 cm and 20–40 cm). In mineral soils, MAOM was the dominant fraction of the C stock (averaged 81.6%). (3) The proportion of C distributed in microaggregates and MAOM increased from Oa+e to the 20–40 cm layer. (4) The C/N ratios and δ13C values of MAOM were smaller and heavier compared to those of POM. Our study demonstrated that in both forests, aggregate formation and mineral association predominantly contributed to SOC storage, and large stocks of SOC were distributed in the deep soil. The increasing proportion of SOC in microaggregates and MAOM along the soil depth, most likely derived from microbial turnover and microbial necromass, influenced SOC stability in both forest types. [ABSTRACT FROM AUTHOR]

Conversion of natural and secondary mixed forests to plantation monocultures can alter soil physical, chemical, and biological properties, which may lead to changes in ecosystem nitrogen (N) status by altering soil N availability. However, assessing and comparing N status between forest types within and across sites remain challenging because different indicators often yield contradicting conclusions. We developed a multiple‐indicator approach to evaluate N status across sites and between larch monocultures and mixed secondary forests paired at three sites (Daxinganling, Maoershan, and Qingyuan) in northeastern China. The selected indicators were foliar N content (%N), soil carbon‐to‐N ratio (C/N), soil inorganic N, foliar 15N natural abundance (δ15N), and δ15N of bulk soil, ammonium, and nitrate in the soil profiles. Our results, as shown mainly by C/N of soil organic layer and the fraction of nitrate in soil inorganic N, showed that N availability increased from north to south in the order Daxinganling < Maoershan < Qingyuan, along with the increasing climatic (mean annual temperature and mean annual precipitation) and N deposition gradients. We also found that the mixed forests had lower N availability than the larch plantations at the two north sites (Daxinganling and Maoershan), while the opposite was found in the south site (Qingyuan). The site‐specific pattern of N availability in the larch versus mixed stands reflects the difference in their succession and management histories. Our study demonstrated that a multiple‐indicator approach is needed for a comprehensive comparison of the N status of different forest types both within and across sites. [ABSTRACT FROM AUTHOR]

The effects of nitrogen (N) deposition on forests largely depend on its fate after entering the ecosystem. While several studies have addressed the forest fate of N deposition using 15N tracers, the long‐term fate and redistribution of deposited N in tropical forests remains unknown. Here, we applied 15N tracers to examine the fates of deposited ammonium (NH4+) and nitrate (NO3‐) separately over 3 years in a primary and a secondary tropical montane forest in southern China. Three months after 15N tracer addition, over 60% of 15N was retained in the forests studied. Total ecosystem retention did not change over the study period, but between 3 months and 3 years following deposition 15N recovery in plants increased from 10% to 19% and 13% to 22% in the primary and secondary forests, respectively, while 15N recovery in the organic soil declined from 16% to 2% and 9% to 2%. Mineral soil retained 50% and 35% of 15N in the primary and secondary forests, with retention being stable over time. The total ecosystem retention of the two N forms did not differ significantly, but plants retained more 15NO3‐ than 15NH4+ and the organic soil more 15NH4+ than NO3‐. Mineral soil did not differ in 15NH4+ and 15NO3‐ retention. Compared to temperate forests, proportionally more 15N was distributed to mineral soil and plants in these tropical forests. Overall, our results suggest that atmospherically deposited NH4+ and NO3‐ is rapidly lost in the short term (months) but thereafter securely retained within the ecosystem, with retained N becoming redistributed to plants and mineral soil from the organic soil. This long‐term N retention may benefit tropical montane forest growth and enhance ecosystem carbon sequestration. [ABSTRACT FROM AUTHOR]

The quantitative role of the canopy size of nurse shrubs on microenvironment and native tree establishment in degraded tropical lands has been seldom studied. In a 21-month field experiment, we aimed to test the effect of a native shrub with different canopy sizes on the early establishment of native trees as part of the effort of forest restoration in tropical China. We examined the microenvironment, and the seedling establishment and growth of two native trees: Castanopsis fissa and Syzygium hancei in both open space (OS) microsite and microsite under the canopy of the native pioneer shrub Rhodomyrtus tomentosa. Shrub microsite was further divided into large canopy (LC), and medium canopy (MC) microsite, based on the shrub leaf area indices. Results showed that relative to OS, LC had higher soil nutrient concentration and water content, and lower photosynthetic active radiation (PAR), while MC had lower PAR and higher soil exchangeable Mg, K, and Ca. Survival and growth were mostly enhanced, while water stress and photoinhibition reduced for C. fissa seedlings in MC and S. hancei seedlings in LC. It is found that the beneficial effects of the native shrub on seedling establishment and growth result mostly from the improvement in nutrient and water availabilities, the reduction in plant stress caused by harsh summer light, and the specific ecological requirements of different tree species. We suggest that different canopy sizes of native shrub R. tomentosa may be explored to target different native trees and hence promote forest restoration in degraded tropical ecosystems. [ABSTRACT FROM AUTHOR]

Aims Forest disturbance from extreme weather events due to climate change could increase the contribution of fresh green leaves to the litter layer of soil and subsequently alter the composition and activity of the soil microbial properties and soil carbon cycling. The objective of this study was to compare the effect of naturally fallen litter and fresh leaves on the soil microbial community composition and their activities. Methods Fresh leaves and normal fallen litter were collected from four tree species (Pinus elliottii, Schima superba, Acacia mangium, A. auriculaeformis) in subtropical China and mixed with soil. Soil microbial community composition was determined using PLFAs, and its activity was quantified by soil respiration. During a 12-month period, the decomposition rate of litter was measured bimonthly using a litterbag method. Soil microbial samples were collected after 6 and 12 months. Soil respiration was measured monthly. Important Findings We found that fresh leaves decomposed faster than their conspecific fallen litter. Although total microbial biomass and bacterial biomass were similar among treatments, soil fungal biomass was higher in fresh leaf than fallen litter treatments, resulting in greater values of the Fungal phospholipid fatty acids (PLFAs)/Bacterial PLFAs ratio. Fungal PLFA values were greater for Schima superba than the other species. The effect of litter type on soil respiration was species-dependent. Specifically, fallen litter released 35% more CO2 than fresh leaves of the conifer P. elliottii. The opposite pattern was observed in the broadleaf species whose fresh leaf treatments emitted 17%–32% more CO2 than fallen litter. Given future predictions that global climate change will cause more disturbances to forests, these results indicate that conifer and broadleaf forests in subtropical China may respond differently to increased fresh litter inputs, with net soil microbial respiration decreasing in conifer forests and increasing in broadleaf forests. [ABSTRACT FROM PUBLISHER]

Background and aims: The relationship between tree species and soil nutrient availability is critical for evaluating plantation succession and promoting forest restoration. This study was conducted to evaluate the impact of exotic and native tress species on soil nutrient availability. Methods: Four exotic species ( Eucalyptus urophylla, E. tereticornis, Acaia auriculaeformis, A. mangium) and four native species ( Castanopsis fissa, Schima superba, C. hystrix, Michelia macclurei) were planted and grown for one-year. Soil solution (DOC, DON, NH−N, NO−N) was sampled and analyzed during the study. After the experiment, soil properties were determined, and plant tissues were analyzed. Results: DOC levels were greater in soils with trees planted than controls without trees. Compared to native species, exotic species had much faster growth rates and greatly reduced DON and NO−N concentrations. Exotic species always had less P concentrations in leaves and stems than native species. Furthermore, N-fixing A. auriculaeformis led to greater soil available P compared to other species. Conclusions: Based on these findings, we provide some recommendations for afforestation practice. This study highlights that a better understanding of the pros and cons of exotic species would be beneficial to advance afforestation in China and the world. [ABSTRACT FROM AUTHOR]

Atmospheric nitrogen (N) deposition in subtropical metropolitan regions has increased greatly because of rapid urbanization, and such increase could lead to N-related changes in soil properties and plant diversity in remnant forests of urban ecosystems. To investigate the pattern of atmospheric N deposition along an urban-rural gradient in metropolitan Guangzhou, southern China, and to assess the potential influence of N deposition on soil properties and understory plant diversity in remnant forests, precipitation, and soil samples were collected and vegetation was surveyed from four forest sites between March 2010 and March 2011. The atmospheric inorganic nitrogen deposition (DIN) decreased with increasing distance from the urban center: DIN inputs were 43.3, 41.2, 35.2, and 30.1 kg N ha year in two urban sites, a suburban site and a rural site, respectively. However, forest soil N status (NH-N, NO-N, and total nitrogen) showed the opposite pattern. Understory herb-layer diversity was negatively correlated to DIN input and positively correlated to soil calcium (Ca) and potassium (K) concentrations and pH; with highest herb-layer diversity found in the rural site receiving the lowest amount of DIN input. These results indicated that higher DIN along with soil acidification and leaching of base cations (Ca and K) might change the current N status and increase nutrients leaching and thereby cause reductions in understory plant diversity. A regional policy linking atmospheric pollution and land protection is needed to protect the most N-sensitive herb species (e.g., forbs and ferns) in these remnant forests. [ABSTRACT FROM AUTHOR]

Abstract: Dissolved inorganic nitrogen (DIN) (as ammonium nitrate) was applied monthly onto the forest floor of one old-growth forest (>400 years old, at levels of 50, 100 and 150kgNha−1 yr−1) and two young forests (both about 70 years old, at levels of 50 and 100kgNha−1 yr−1) over 3 years (2004–2006), to investigate how nitrogen (N) input influenced N leaching output, and if there were differences in N retention between the old-growth and the young forests in the subtropical monsoon region of southern China. The ambient throughfall inputs were 23–27kgNha−1 yr−1 in the young forests and 29–35kgNha−1 yr−1 in the old-growth forest. In the control plots without experimental N addition, a net N retention was observed in the young forests (on average 6–11kgNha−1 yr−1), but a net N loss occurred in the old-growth forest (−13kgNha−1 yr−1). Experimental N addition immediately increased DIN leaching in all three forests, with 25–66% of added N leached over the 3-year experiment. At the lowest level of N addition (50kgNha−1 yr−1), the percentage N loss was higher in the old-growth forest (66% of added N) than in the two young forests (38% and 26%). However, at higher levels of N addition (100 and 150kgNha−1 yr−1), the old-growth forest exhibited similar N losses (25–43%) to those in the young forests (28–43%). These results indicate that N retention is largely determined by the forest successional stages and the levels of N addition. Compared to most temperate forests studied in Europe and North America, N leaching loss in these seasonal monsoon subtropical forests occurred mainly in the rainy growing season, with measured N loss in leaching substantially higher under both ambient deposition and experimental N additions. [Copyright &y& Elsevier]

The impacts of anthropogenic nitrogen (N) deposition on forest ecosystems depend in large part on its fate. However, our understanding of the fates of different forms of deposited N as well as the redistribution over time within different ecosystems is limited. In this study, we used the 15N‐tracer method to investigate both the short‐term (1 week to 3 months) and long‐term (1–3 yr) fates of deposited NH4+ or NO3− by following the recovery of the 15N in different ecosystem compartments in a larch plantation forest and a mixed forest located in northeastern China. The results showed similar total ecosystem retention for deposited NH4+ and NO3−, but their distribution within the ecosystems (plants vs. soil) differed distinctly particularly in the short‐term, with higher 15NO3− recoveries in plants (while lower recoveries in organic layer) than found for 15NH4+. The different short‐term fate was likely related to the higher mobility of 15NO3− than 15NH4+ in soils instead of plant uptake preferences for NO3− over NH4+. In the long‐term, differences between N forms became less prevalent but higher recoveries in trees (particularly in the larch forest) of 15NO3− than 15NH4+ tracer persisted, suggesting that incoming NO3− may contribute more to plant biomass increment and forest carbon sequestration than incoming NH4+. Differences between the two forests in recoveries were largely driven by a higher 15N recovery in the organic layer (both N forms) and in trees (for 15NO3−) in the larch forest compared to the mixed forest. This was due to a more abundant organic layer and possibly higher tree N demand in the larch forest than in the mixed forest. Leachate 15N loss was minor (<1% of the added 15N) for both N forms and in both forests. Total 15N recovery averaged 78% in the short‐term and decreased to 55% in the long‐term but with increasing amount of 15N label (re)‐redistributed into slow turn‐over pools (e.g., trees and mineral soil). The different retention dynamics of deposited NH4+ and NO3− may have implications in environmental policy related to the anthropogenic emissions of the two N forms. [ABSTRACT FROM AUTHOR]

Elevated nitrogen (N) deposition due to intensified emissions of NH 3 and NO x is a global problem with profound consequences on living organisms and the environment. Although N emission rates are currently considered to be high in East Asia, reports on the current N deposition level and composition are still limited, especially in northeastern China, where official N deposition monitoring sites are unavailable. This limits our understanding of the spatio-temporal N deposition patterns and their influencing factors at regional to continental scales. Here, we used data collected mostly during 2019 at 38 sites, comprising 7 sites in northeastern China and 31 EANET (Acid Deposition Monitoring Network in East Asia) sites in middle and east Russia, Mongolia, central and southern China, South Korea and Japan to explore the spatial-seasonal variations and drivers of ammonium and nitrate deposition across the Northeast Asia. Total bulk inorganic N (TIN) deposition was 3.7–24.5 kg N ha−1 yr−1 and NH 4 +-N/NO 3 −-N ratio in the TIN was 0.8–2.8 in northeastern China. The bulk/wet TIN deposition averaged 7.5 kg N ha−1 yr−1 (predominantly in the form of ammonium-N: NH 4 +-N/NO 3 −-N = 1.4) over the Northeast Asia region, with the highest rates being observed in northeastern China (11.6), as well as central and southern China (10.7), followed by east Russia, South Korea and Japan (5.6), and the lowest in middle Russia and Mongolia (1.5). This regional bulk/wet TIN deposition level is about twice of the wet TIN deposition level in Europe and the United States. The TIN deposition in summer and spring was 45–467% higher than in autumn and winter. Out of the ten land uses considered, only agricultural and urban land uses significantly positively correlated with NH 4 +-N and NO 3 −-N deposition rates across all monitored sites. This study suggests that the ongoing agricultural and urban expansions are likely to enhance N deposition and its associated effects across global ecosystems. [Display omitted] • Total inorganic N deposition was 3.7–24.5 kg N ha−1 yr−1 in northeastern China. • TIN deposition ranged 0.4–24.5 and averaged 7.5 kg N ha−1 yr−1 over Northeast Asia. • NH 4 +-N dominated TIN deposition (NH 4 +-N/NO 3 −-N = 1.4) in Northeast Asia. • TIN deposition level in NE Asia is about twice that reported in Europe and the USA. • NH 4 +-N and NO 3 −-N deposition increased with increasing farmland and urban coverage. [ABSTRACT FROM AUTHOR]

The impacts of anthropogenic nitrogen (N) deposition on forest ecosystems have been well recognized. However, our understanding of the fate of deposited N and its retention dynamics in different ecosystems is limited. This study used the 15N-tracer method to investigate both the short-term (1 week - 3 months) and long-term (1 - 3 years) fates of deposited NH4+ or NO3- in two forests in northeastern China, namely a larch plantation forest and a mixed forest. We determined retention dynamics of 15N-labelled NH4+ or NO3- (by following the recovery of the 15N) in different ecosystem compartments over three years. In the first three months, total N retention declined from 97 -100% to 52 - 72% in the larch forest and from 84 - 88 to 53 - 56% in the mixed forest, indicating a rapid initial loss of newly deposited N regardless of forest type. Here after, 15N retention stayed relatively constant in both forests, but retained 15N was redistributed from the organic layer to the mineral soil with no significant change in plants over time. At the end of three years, 15N retention were 48 - 51% and 42 - 47% in the larch and mixed forest, respectively, suggesting that once retained over the first growing season, most deposited N was recycled within ecosystem in the long-term. The N retention efficiency in our studied forests was lower than that observed in many temperate forests in Europe and US. But leachate 15N loss was minor (<1% of the added 15N). Total N retention did not significantly differ between NH4+ and NO3- inputs in either forest. However, the distribution of NH4+ and NO3- inputs in different ecosystem compartments was distinctly different, with higher 15NO3- retained in plants (while lower retention in organic layer) than found for 15NH4+. This suggests that NO3- deposition could be more beneficial to forest growth and CO2 sequestration into plant biomass. The distinctly different retention of deposited NH4+ and NO3- may have long-term consequences, which has important implications in environmental policy development to regulate anthropogenic deposition of NO3- and NH4+ and their impacts on forest ecosystems.Keywords: 15N tracer, temperate forests, N retention and redistribution, N deposition, northeastern China [ABSTRACT FROM AUTHOR]

• First long-term daily soil NO flux measurement with an automated system from a temperate forest in Northeast China. • Soil temperature explained 90–92% of the seasonal variation in NO emission, with a Q 10 of 3.67. • The optimum soil moisture for NO emission was 37% WFPS during the growing season. • Annual soil NO emission was 0.42±0.04 kg N ha−1, being 31% of the global forest average. • Soil NO emission during the non-growing season was only 7.7% of the annual flux. Nitric oxide (NO) is a highly reactive trace gas affecting atmospheric chemistry and air quality. Although forest soils have been recognized as an important source of atmospheric NO, there are large uncertainties in global forest soil NO emission inventories (ranged from 0.03 to 8.00 kg N ha−1, averaged 1.34 ± 0.28 kg N ha−1), partly due to the paucity of high-frequency monitoring from unmanaged forests. In this study, we used an automated sampling system to measure NO fluxes with a high temporal resolution over two years (daily measurements from January 2019 to December 2020) in a mixed forest in Northeast China. We found that the mean annual NO emission was 0.42 ± 0.04 kg N ha−1, being 31% of the global forest average. The contribution of NO emission during the growing season was 92% of the yearly NO flux. Soil temperature was the most important edaphic factor in regulating NO emission, explaining 90–92% of the seasonal variation. The apparent temperature sensitivity (Q 10) of NO flux was 3.67. In the growing season, NO emission was also influenced by soil moisture, with optimum soil moisture of 37% WFPS. By providing a detailed measurement of diurnal, seasonal, and annual dynamics of NO emissions and their environmental controls from forest soils, our data are useful to develop more accurate biogeochemical models that will improve upscaled global NO budgets. [ABSTRACT FROM AUTHOR]

Maize (Zea mays L.) is one of most important crops in China, and its cultivation increasedrapidly in the last decades. High doses of nitrogen (N) fertilizers are widely applied for highgrain yield. Quantifying the fates of fertilizer N, especially the use efficiency by abovegroundbiomass (NUE) and their losses to the environment and the atmosphere, is critical for localagricultural management. However, up to now, it is not clear on fate of N fertilizer and howand how much the applied nitrogen is lost, particularly by the various forms of gaseousN. We have conducted six new 15N tracer experiments and combined previous results toevaluate the fates of N fertilizer in maize cropping systems across China. In order to accuracyevaluate the gaseous N loss, a fully automated measuring system was built to simultaneouslymeasure soil N2O and NO emissions in 2017 and 2018 for a typical maize filed in NortheastChina; to identify the source (soil N or fertilizer N) of gases of NO, N2O and NH3,another field experiment was conducted in the adjacent field using 15N-labeledfertilizer. We found that, on average, 34%, 35% and 31% of the applied N fertilizer (averagely 222kg N ha−1, n = 23) was taken up by crop, retained in the soil and lost to the environment,respectively. The results of the automated measuring system showed that the release ratesof NO and N2O were 9.1 and 2.6 kg N ha−1 in 2017, 2.6 and 2.2 kg N ha−1in2018, respectively. Relatively high NO emission rate in 2017 might been caused byrelatively low annual precipitation in that year (437 mm in 2017 and 581 mm in2018). The results of the static chamber system showed that the release rates of NH3,NO and N2O during the maize growing period were only 1.6, 1.8 and 1.4 kg Nha−1, respectively, while NO and N2O emission using this method being muchlower compared to the auto system with high resolution. 15N labeling experimentshowed that 67%, 52% and 29% of the released NH3, NO and N2O came fromthe applied fertilizer N. Seasonal patterns of soil NO and N2O emissions weresimilar, indicating they were controlled by similar factors. Among the factors, soiltemperature and moisture were significantly related to the emissions of NO and N2O,and soil temperature was significantly controlling the NO/N2O ratio in this studysite. Key words: nitrogenous gases losses, maize crop, nitrogen fertilization, 15N trace,nitrogen use efficiency (NUE) [ABSTRACT FROM AUTHOR]

Resource integration of coal enterprises is conducive to reducing pollution and carbon emissions, thus alleviating environmental problems such as global warming. Government regulation has a great influence on enterprise behavior. Therefore, it is necessary to analyze the strategies of government and coal enterprises in resource integration. Based on the perspective of government regulation, this paper discusses how to guide and restrict coal enterprises to conduct resource integration behavior, and whether the government supervises this behavior. First, through empirical research, government regulations of coal enterprises are given practical policy implications. Second, using evolutionary game and simulation technology, from the perspective of government regulation, we explore the complex behavioral interaction mechanism between the dominant and inferior coal enterprises, the mechanism between the government and coal enterprises, and analyze the impact of key factors on the dynamic evolution process. Finally, the sensitivity analysis of the selected parameters is discussed in details, which provides useful decision-making suggestions for the government and enterprises. In addition, this paper further analyzes the impact of different government policies on coal enterprises' green innovation strategies. Results demonstrate that (1) when the power gap between enterprises is large, the probability of dominant enterprises choosing resource integration converges to 1, while the probability of inferior enterprises converges to 0. Therefore, government regulations are invalid for inferior enterprises; (2) the combination of government regulations can help improve the efficiency of coal enterprises' strategic choices. With the increase in the intensity of government rewards and punishments, the probability of enterprise resource integration evolves from 0 to 1; (3) excessive government regulations make the choice between the government and coal companies tend to swing, because the probability of the two is between 0 and 1. Therefore, excessive government regulations cannot effectively achieve resource integration and government regulation. (4) The government subsidy strategy is less effective than the government's pollution penalty strategy in promoting the green innovation of enterprises. Our research shows that the government should choose different policy combinations and intensities to regulate resource integration according to the market power of coal enterprises, which provides theoretical reference and practical guidance for the government to regulate corporate resource integration behavior., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Nitric oxide (NO) plays a critical role in atmospheric chemistry and also is a precursor of nitrate, which affects particle matter formation and nitrogen deposition. Agricultural soil has been recognized as a main source of atmospheric NO. However, quantifying the NO fluxes emitted from croplands remains a challenge and in situ long-term measurements of NO are still limited. In this study, we used an automated sampling system to measure NO fluxes with a high temporal resolution over two years (April 2017 to March 2019) from a rainfed maize field in the Northeast China. The cumulative annual NO emissions were 8.9 and 2.3 kg N ha -1 in year 1 (April 2017 to March 2018) and year 2 (April 2018 to March 2019), respectively. These interannual differences were largely related to different weather conditions encountered. In year 1, a month-long drought before and after the seeding and fertilizing reduced plant N uptake and dramatically increased soil N concentration. The following moderate rainfalls promoted large amount of NO emissions, which remained high until late September. The NO fluxes in both years showed clearer seasonal patterns, being highest after fertilizer application in summer, and lowest in winter. The seasonal patterns of NO fluxes were mainly controlled by soil available N concentrations and soil temperatures. The contribution of NO fluxes during the spring freeze-thaw in both years was no more than 0.2% of the annual NO budget, indicating that the freeze-thaw effect on agricultural NO emissions was minimal. In addition, with high-resolution monitoring, we found that soil not only act as a NO source but also a sink. Long-term and high-resolution measurements help us better understand the diurnal, seasonal, and annual dynamics of NO emissions, build more accurate models and better estimate global NO budget and develop more effective policy responses to global climate change., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Nitrification is a crucial step in ecosystem nitrogen (N) cycling, but scaling up from plot-based measurements of gross nitrification to catchments is difficult. Here, we employed a newly developed method in which the oxygen isotope anomaly (Δ 17 O) of nitrate (NO 3 ) is used as a natural tracer to quantify in situ catchment-scale gross nitrification rate (GNR) for a temperate forest from 2014 to 2017 in northeastern China. The annual GNR ranged from 71 to 120 kg N ha - ) is used as a natural tracer to quantify in situ catchment-scale gross nitrification rate (GNR) for a temperate forest from 2014 to 2017 in northeastern China. The annual GNR ranged from 71 to 120 kg N ha -1 yr -1 (average 94 ± 10 kg N ha -1 yr -1 ) over the 4 years in this forest. This result and high stream NO 3 - loss (4.2-8.9 kg N ha -1 yr -1 ) suggest that the forested catchment may have been N-saturated. At the catchment scale, the total N output of 10.7 kg N ha -1 yr -1 , via leaching and gaseous losses, accounts for 56% of the N input from bulk precipitation (19.2 kg N ha -1 yr -1 ). This result indicates that the forested catchment is still retaining a large fraction of N from atmospheric deposition. Our study suggests that estimating in situ catchment-scale GNR over several years when combined with other conventional flux estimates can facilitate the understanding of N biogeochemical cycling and changes in the ecosystem N status.

The impacts of anthropogenic nitrogen (N) deposition on forest ecosystems depend in large part on its fate. However, our understanding of the fates of different forms of deposited N as well as the redistribution over time within different ecosystems is limited. In this study, we used the 15 N-tracer method to investigate both the short-term (1 week to 3 months) and long-term (1-3 yr) fates of deposited NH 4 + or NO 3 N in different ecosystem compartments in a larch plantation forest and a mixed forest located in northeastern China. The results showed similar total ecosystem retention for deposited NH - by following the recovery of the 15 N in different ecosystem compartments in a larch plantation forest and a mixed forest located in northeastern China. The results showed similar total ecosystem retention for deposited NH 4 + and NO 3 - , but their distribution within the ecosystems (plants vs. soil) differed distinctly particularly in the short-term, with higher 15 NO 3 - recoveries in plants (while lower recoveries in organic layer) than found for 15 NH 4 + . The different short-term fate was likely related to the higher mobility of 15 NO 3 - than 15 NH 4 + in soils instead of plant uptake preferences for NO 3 - over NH 4 + . In the long-term, differences between N forms became less prevalent but higher recoveries in trees (particularly in the larch forest) of 15 NO 3 - than 15 NH 4 + tracer persisted, suggesting that incoming NO 3 - may contribute more to plant biomass increment and forest carbon sequestration than incoming NH 4 + . Differences between the two forests in recoveries were largely driven by a higher 15 N recovery in the organic layer (both N forms) and in trees (for 15 NO 3 - ) in the larch forest compared to the mixed forest. This was due to a more abundant organic layer and possibly higher tree N demand in the larch forest than in the mixed forest. Leachate 15 N loss was minor (<1% of the added 15 N) for both N forms and in both forests. Total 15 N recovery averaged 78% in the short-term and decreased to 55% in the long-term but with increasing amount of 15 N label (re)-redistributed into slow turn-over pools (e.g., trees and mineral soil). The different retention dynamics of deposited NH 4 + and NO 3 - may have implications in environmental policy related to the anthropogenic emissions of the two N forms., (© 2019 by the Ecological Society of America.)