Effects of nitrogen deposition on the carbon budget and water stress in Central Asia under climate change

Atmospheric deposition of nitrogen(N)plays a significant role in shaping the structure and functioning of various terrestrial ecosystems worldwide.However,the magnitude of N deposition on grassland ecosystems in Central Asia still remains highly uncertain.In this study,a multi-data approach was adopted to analyze the distribution and amplitude of N deposition effects in Central Asia from 1979 to 2014 using a process-based denitrification decomposition(DNDC)model.Results showed that total vegetation carbon(C)in Central Asia was 0.35(±0.09)Pg C/a and the averaged water stress index(WSI)was 0.20(±0.02)for the whole area.Increasing N deposition led to an increase in the vegetation C of 65.56(±83.03)Tg C and slightly decreased water stress in Central Asia.Findings of this study will expand both our understanding and predictive capacity of C characteristics under future increases in N deposition,and also serve as a valuable reference for decision-making regarding water resources management and climate change mitigation in arid and semi-arid areas globally.

Geographical Distribution of Atmospheric Nitrogen Deposition in China and Its Response to Emission Control Policy

Atmospheric nitrogen(N)deposition has experienced significant change because of anthropogenic emissions,thereby exert-ing a pronounced impact on global ecosystem services.With the rapid development of industry and agriculture and the swift expansion of urban areas in China since the 1980s,reactive nitrogen(Nr)emissions and N deposition have substantially increased.In pursuit of im-proving air quality,China has implemented a series of environmental protection policies and undertaken diverse measures to reduce pol-lutant emissions.This paper is a review of multivariate data sources of atmospheric N deposition based on the results of literature from 1980 to 2023,and the original data from 1980 to 2020 are summarized,counted and calculated.The main findings are as follows:1)the annual average atmospheric N deposition ranged from approximately 20-40 kg/(ha·yr),with the variability primarily linked to different assessment methods;2)regional disparities were evident in the spatial distribution of N deposition,with elevated values concentrated in areas with intense Nr emissions;3)atmospheric N deposition significantly declined after 2010,particularly the deposition of oxidized N,while reduced N deposition remained stable.These results reflect the effects of China's serious control policies on nitrogen oxide(NO.)emissions and strengthen the importance of agricultural NH3 emission mitigation.This study contributes to a comprehensive understand-ing of the N dynamics in the emission-deposition process,and provides a scientific foundation for the research of environmental protec-tion,climate change,and sustainable development.

Nitrogen Deposition and Its Spatial Pattern in Main Forest Ecosystems along North-South Transect of Eastern China

A continuous three-year observation(from May 2008 to April 2011)was conducted to characterize the spatial variation of dissolved inorganic nitrogen(DIN)deposition at eight main forest ecosystems along the north-south transect of eastern China(NSTEC).The results show that both throughfall DIN deposition and bulk DIN deposition increase from north to south along the NSTEC.Throughfall DIN deposition varies greatly from 2.7 kg N/(ha·yr)to 33.0 kg N/(ha·yr),with an average of 10.6 kg N/(ha·yr),and bulk DIN deposition ranges from 4.1 kg N/(ha·yr)to 25.4 kg N/(ha·yr),with an average of 9.8 kg N/(ha·yr).NH4+-N is the dominant form of DIN deposition at most sampling sites.Additionally,the spatial variation of DIN deposition is controlled mainly by precipitation.Moreover,in the northern part of the NSTEC,bulk DIN deposition is 17%higher than throughfall DIN deposition,whereas the trend is opposite in the southern part of the NSTEC.The results demonstrate that DIN deposition would likely threaten the forest ecosystems along the NSTEC,compared with the critical loads(CL)of N deposition,and DIN deposition in this region is mostly controlled by agricultural activities rather than industrial activities or transportation.

Influence of climate warming and nitrogen deposition on soil phosphorus composition and phosphorus availability in a temperate grassland,China

Climate warming and nitrogen （N） deposition change ecosystem processes, structure, and functioning whereas the phosphorus （P） composition and availability directly influence the ecosystem structure under condi- tions of N deposition. In our study, four treatments were designed, including a control, diurnal warming （DW）, N deposition （ND）, and combined warming and N deposition （WN）. The effects of DW, ND, and WN on P composition were studied by 3~p nuclear magnetic resonance （3~p NMR） spectroscopy in a temperate grassland region of China. The results showed that the N deposition decreased the soil pH and total N （TN） concentration but increased the soil OIsen-P concentration. The solution-state 31p NMR analysis showed that the DW, ND and WN treatments slightly decreased the proportion of orthophosphate and increased that of the monoesters. An absence of myo-inositol phosphate in the DW, ND and WN treatments was observed compared with the control. Furthermore, the DW, ND and WN treatments significantly decreased the recovery of soil P in the NaOH-EDTA solution by 17%-20%. The principal component analysis found that the soil pH was positively correlated with the P recovery in the NaOH-EDTA solution. Therefore, the decreased soil P recovery in the DW and ND treatments might be caused by an indirect influence on the soil pH. Additionally, the soil moisture content was the key factor limiting the available P. The positive correlation of total carbon （TC） and TN with the soil P composition indicated the influence of climate warming and N deposition on the biological processes in the soil P cycling.

Ecological effects of atmospheric nitrogen deposition on soil enzyme activity

The continuing increase in human activities is causing global changes such as increased deposition of atmospheric nitrogen. There is considerable interest in understanding the effects of increasing atmospheric nitrogen deposition on soil enzyme activities, specifically in terms of global nitrogen cycling and its potential future contribution to global climate change. This paper summarizes the ecological effects of atmospheric nitrogen deposition on soil enzyme activities, including size-effects, stage-effects, site-effects, and the effects of different levels and forms of atmospheric nitrogen deposition. We discuss needs for further research on the relationship between atmospheric nitrogen deposition and soil enzymes.

Effects of Nitrogen Deposition on Tundra Vegetation Undergoing Invasion by Deyeuxia angustifolia in Changbai Mountains

In recent years, herbaceous species such as Deyeuxia angustifolia （Kom.） Y. L. Chang has invaded alpine tundra regions of the western slope of the Changbai Mountains. Because atmospheric nitrogen deposition is predicted to increase under a warming climate and D. angustifolia is sensitive to nitrogen addition, field experiments were conducted from 2010 to 2013 to determine the effect of increased nitrogen deposition on the mechanisms of D. angustifolia invasion. The goal of this study is to evaluate the impact of increased nitrogen deposition on the changes in alpine tundra vegetation （consisting mostly of Rhododendron chrysanthum Pall. and Vaccinium uliginosum Linn.）. The results showed that： 1） simulated nitrogen deposition affected overall characteristics and structure of R. chrysanthum and E uliginosum communities and had a positive impact on the growth of tundra vegetation invaded by 1）. angustifolia; 2） R. chrysanthum was more resistant to invasion by D. angustifolia than V.. uliginosum; 3） simulated nitrogen deposition could improve the growth and enhance the competitiveness of D. angustifolia, which was gradually replacing R. chrysanthum and V. uliginosum and might become the dominant species in the system in future, transforming alpine tundra into alpine meadow in the Chanebai Mountains.

Ammonia should be considered in field experiments mimicking nitrogen deposition

Excess nitrogen deposition has significant impacts on water eutrophication,soil acidification,eleveted greenhouse gas emissions,and biodiversity loss.These impacts mostly derive from conventional manipulative experiments in the field by adding nitrogen solution directly onto grassland or forest floors.For forest ecosystems,previous field experiments have usually ignored the nitrogen cycles in the canopy,which are important in responses to airborne nitrogen input.Although whole-forest canopy nitrogen fertilization has recently been conducted to promote our understanding of nitrogen deposition processes,spraying nitrogen solution onto plants still largely ignores the dry deposition of ammonia(as well as other gaseous reactive nitrogen species).To date,there have been a limited number of field studies that have investigated the bi-directional exchange of ammonia between the atmosphere and plants,not to mention the impacts of ammonia on natural ecosystems.Due to the increasing trend of atmospheric ammonia concentrations worldwide and its dominant role in nitrogen deposition and haze pollution,the next generation of experiments should mimick nitrogen deposition on natural ecosystems by further considering the dry deposition of ammonia.

Atmospheric nitrogen deposition in Yangtze River Delta:insights gained from the nitrogen content and isotopic composition of the moss Haplocladium microphyllum

Simple and inexpensive estimation of the rates and sources of atmospheric nitrogen(N)deposition is critical for its effective mitigation in a region with different land-use types.In this study,the N content and N isotopic composition(δ15N)of moss(Haplocladium microphyllum)tissues and precipitation at six sites with three land-use types(urban,suburban,and rural)were measured in the Yangtze River Delta.A significant linear relationship between moss N content and wet N deposition,and a consistent decrease trend for moss N content and wet N deposition from urban to suburban to rural areas were observed.More negativeδ15N of suburban and rural mosses indicated N mainly released from agriculture and effluent,while the less negativeδ15N of urban mosses were mainly influenced by fossil fuel combustion and traffic emissions.Although the negative mossδ15N indicates that reduced N dominates wet N deposition,there was no significant correlation between mossδ15N and the ratio of ammonium to nitrate(NH4+/NO3−).These results reveal that the moss N content andδ15N can be used as a complementary tool for estimating the rates and sources of wet N deposition in a region with different land-use types.

Topography modulates effects of nitrogen deposition on microbial resource limitation in a nitrogen-saturated subtropical forest

Background:Nitrogen(N)saturation theory proposes that an ecosystem might switch from N limitation to carbon(C),phosphorus(P),or other nutrient limitations if it receives continuous N input.Yet,after N limitation is removed,which nutrient is the most limited and whether topography modulates such change is rarely tested at a microbial level.Here,we conducted a two-year N addition experiment under two different topography positions(i.e.a slope and a valley)in a N-saturated subtropical forest.Soil enzyme activity was measured,and ecoenzymatic stoichiometry indexes were calculated as indicators of microbial resource limitation.Results:In the valley,two-year N addition changed the activity of all studied enzymes to various degrees.As a result,microbial C limitation was aggravated in the valley,and consequently microbial decomposition of soil labile organic C increased,but microbial P limitation was alleviated due to the stoichiometry balance.On the slope,however,N addition did not significantly change the activity of the studied enzymes,and did not alter the status of microbial resource limitation.Conclusions:These results indicate that C is a more limited element for microbial growth than P after removing N limitation,but we also highlight that topography can regulate the effect of N deposition on soil microbial resource limitation in subtropical forests.These findings provide useful supplements to the N saturation theory.

Short-term Effects of Nitrogen Deposition on Soil Physical and Chemical Properties of Tibetan Forest-Grassland Landscape Boundary

[Objective] The paper was to study the effects of nitrogen deposition on soil nutrients and soil dissolved organic carbon in forest-grassland landscape in Linzhi, Tibet, and to provide scientific basis and basic data for understanding and assessing the effect of atmospheric nitrogen deposition on soil nutrients and soil dissolved organic carbon. [Method] From July 2014 to August 2015, in situ nitrogen deposition （CK0 kg· hm^2/a, LN25 kg·hm^2/a, MN 50 kg·hm^2/a, HN 150 kg· hm^2/a） was simulated in the forestgrassland boundary of Zhuqudeng village, Bujiu Township, LinzhiCounty, Tibet. The soil samples were collected for analyzing nutrient and dissolved contents in the soil layer of 0-20 and 20-40 cm. The effects ofdifferent nitrogen deposition levels on soil nutrients and dissolved organic carbon （DOC） were studied. [Result] Nitrogen deposition had significantimpacts on soil organic matter, total N, total P, total K, available N, available P, available K, exchangeable Ca, exchangeable Mg, pH, and DOC（P〈0.05）. （2） With the deepening of nitrogen deposition from CK, LN, MN to HN in the 0-20 cm boundary soil, the contents of organic matter, total N,total P, available P, exchangeable Ca, exchangeable Mg and DOC kept decreasing, and the content of total K and available N increased continuously. The pH increased in LN treatment and decreased in HN treatment, while the available K content was decreased in LN and HN treatment, butincreased in MN treatment. （3） The contents of organic matter, total N, total P, available N, available P, exchangeable Ca, exchangeable Mg andDOC all decreased at the soil layer of 20-40 cm under the same nitrogen deposition. The pH increased in LN treatment, but decreased in HN treatment; the content of total K decreased in LN treatment and increased in MN and HN treatments; the content of available K decreased in LN andHN treatments, but increased in MN treatment. （4） With the deepening of boundary soil layer （0-20 to 20-40 cm）, the organic matter, total N, totalP, available P, available K, exchangeable Ca, exchangeable Mg, DOC showed the same response to simulated nitrogen deposition, while the available N and total K responded differently. [Conclusion] Different levels of N deposition had certain impact on soil nutrient, and the variation of soilnutrients was not the same at different levels.

The Effect of Nitrogen Deposition on Soil Microorganisms in the Woodland-Grassland Border of Tibet

Nitrogen deposition was simulated from July 2014 to August 2015 in the grassland, woodland, and woodland-grassland border in Zhuqudeng Village, Bujiu Township, Linzhi County,(CK, 0 kg·hm^2·a^(-1); LN, 25 kg·hm^2·a^(-1), MN, 50 kg·hm^2·a^(-1); HN, 150 kg·hm^2·a^(-1)). NH_4NO_3 was used as nitrogen source to analyze the number of microorganisms in soil layers of 0–20 cm and 20–40 cm and explore the effect of different degrees of nitrogen deposition on soil microorganisms in grassland, woodland, and woodlandgrassland border. The results showed that: the number of bacteria in the grassland increased significantly under the treatment of LN, and the number of bacteria in the woodland-grassland border and woodland had a rising response under the influence of nitrogen deposition; the number of actinomycetes in the grassland increased in MN and HN treatment, and significantly increased in the border and woodland under LN treatment; the number of molds decreased sharply in the grassland, woodland, and woodland-grassland border.

Nitrogen Deposition Via N^+ Implantation:Implications for Primordial Amino Acids Synthesis Revisited

In this paper amino acids synthesis in aqueous solution induced by ion implantation, which was possibly ubiquitous on primitive Earth, is investigated. As a discharge using a graphite rod as the anode under a nitrogen atmosphere was performed against ammonia water, it was found that three kinds of amino acids were produced. They were glycine, serine and alanine. By introducing ion implantation into the carboxylate solution, ammonia and amino acids were also formed via nitrogen deposition/fixation. Another isotopic experiment showed that both OH and H radicals played a crucial role in the arc-discharge-promoted reactions in aqueous solution Therefore, we believe that the impact of ions in the original atmospheric conditions might have functioned as a promoter in the chemical origin and evolution of life.

The Effect of Nitrogen Deposition on Soil Enzyme Activity in the Forest Grassland Landscape Boundary of Tibet

The simulated nitrogen deposition [control check （CBQ, 0 kg＇hm^2 /a; low nitrogen （LN）, 25 kg-hm^2 /a; medium nitrogen （MN）, 50 kg-hm^2/a high nitrogen （HN）, 150 kg·hm^2 /a] was performed from July 2014 to August 2015 in the fotest-gtassland boundary in Zhuqudeng Village, Bujiu Township, Iinzhi City, Tibet Autonomous Regioii to analyze the activity of enzymes （invertase, catalase, ufease, amylase, cellukse, polyphenol oxidase, and p-glucosidase） in soil layers of 0-20 cm and 20-40 cm and explore die effect of different levels of nitrogen deposition on enzyme activity different layers of soiL The results showed tiiat＇ ① different levels of simulated nitrogen deposition had rematkable effects on sucrase, amylase, cellukse, polyphenol oxidase and p-gjucosidase in the soil layer of 0-20 cm （p 〈 0.05） and unrematkable effects on catalase and urease （p 〉 0.05）; in the soil layer of 2CM0 cm, the response made by suctase, catalase, urease, amylase, cellulase, polyphenol oxidase and p-glucosidase to nitrogen deposition reached a significant level 〈 0.05）.② In the soil layer of 0-20 cm, the activity of ufease and polyphenol oxidase reduced under LN treatment and enhanced under HN treatment, and the activity of invertase, catalase, amylase, cellulose, and p-glucosidase was inhibited by nitrogen deposition. ③In the soil layer of 2CM0 cm, the activity of polyphenol oxidase and p-glucosidase reduced under under LN treatment and enhanced under HN treatment, and the activity of invertase, catalase, urease, amylase, and cellulase was inhibited by nitrogen deposition. ④ With the deepening of the boundary soil layer （from 0-20 cm to 20-40 cm）, urease and pucosidase made different responses to the different levels of nitrogen deposition, while invertase, catakse, amylase, cellulose, and polyphenol oxidase showed the same response to nitrogen deposition.

Short-term Effects of Nitrogen Deposition on Soil Enzyme Activities in Tibet Grasslands

[Objective] The paper was to study the effects of nitrogen deposition on enzyme activity in different layers of soil. [Method] With grass-land located in Zhuqudeng Village, Bujiu Township, Linzhi City, the Tibet Autonomous Region, as the object, nitrogen deposition was simulated from July 2014 to August 2015. Four N addition treatments were established： control （0 kg·hm^2/a）, low N （LN, 25kg·hm^2/a）, medium N （MN, 50 kg·hm^2/a） and High N （HN, 150 kg·hm^2/a）, aiming at measuring enzyme activity （invertase, catalase, urease, amylase, cellulase, polyphenol oxidase and β-glucosi- dase） in different layers of grassland soil （0 -20 cm and 20-40 cm）. [Result] （1） Different levels of simulated nitrogen deposition had significant impact on invertase and β-glucosidase at the soil depth of 0-20 cm （P〈0.05）, but no significant impact on catalase, urease, amylase, cellulase and polyphenol oxidase（P〉0.05）; invertase, polyphenol oxidase and β-glucosidase had significant response to nitrogen deposition at the soil depth of 20- 40 cm （P〈0.05）, while catalase, urease, amylase and cellulose had no significant response （P〉0.05）. （2） The activities of invertase and polyphenol oxidase were enhanced at the soil depth of 0-20 cm, and that of β-glucosidase was inhibited. （3） With the deepening of nitrogen deposition, the ac- tivities of invertase and cellulose were enhanced at the soil depth of 20-40 cm; the activity of polyphenol oxidase was reduced in LN treatment, but increased in HN treatment; the activity of β-glucosidase was increased in LN treatment, but decreased in MN treatment. （4） With the deepening of soil layers, invertase and polyphenol oxidase responded similarly to simulated nitrogen deposition. [Conclusion] The results provide certain scientific basis and fundamental data for better understanding and evaluating the effects of nitrogen deposition on enzyme activity in grassland soil.

Nitrogen deposition mediates more stochastic processes in structuring plant community than soil microbial community in the Eurasian steppe

Anthropogenic environmental changes may affect community assembly through mediating both deterministic(e.g.,competitive exclusion and environmental filtering)and stochastic processes(e.g.,birth/death and dispersal/colonization).It is traditionally thought that environmental changes have a larger mediation effect on stochastic processes in structuring soil microbial community than aboveground plant community;however,this hypothesis remains largely untested.Here we report an unexpected pattern that nitrogen(N)deposition has a larger mediation effect on stochastic processes in structuring plant community than soil microbial community(those<2 mm in diameter,including archaea,bacteria,fungi,and protists)in the Eurasian steppe.We performed a ten-year nitrogen deposition experiment in a semiarid grassland ecosystem in Inner Mongolia,manipulating nine rates(0–50 g N m^(-2)per year)at two frequencies(nitrogen added twice or 12 times per year)under two grassland management strategies(fencing or mowing).We separated the compositional variation of plant and soil microbial communities caused by each treatment into the deterministic and stochastic components with a recently-developed method.As nitrogen addition rate increased,the relative importance of stochastic component of plant community first increased and then decreased,while that of soil microbial community first decreased and then increased.On the whole,the relative importance of stochastic component was significantly larger in plant community(0.552±0.035;mean±standard error)than in microbial community(0.427±0.035).Consistently,the proportion of compositional variation explained by the deterministic soil and community indices was smaller for plant community(0.172–0.186)than microbial community(0.240–0.767).Meanwhile,as nitrogen addition rate increased,the linkage between plant and microbial community composition first became weaker and then became stronger.The larger stochasticity in plant community relative to microbial community assembly suggested that more stochastic strategies(e.g.,seeds addition)should be adopted to maintain above-than below-ground biodiversity under the pressure of nitrogen deposition.

Elevated nitrogen deposition may advance invasive weed, Solidago canadensis, in calcareous soils

Aims change in nitrogen(N)availability regulates phosphorus(P)acquisition and potentially alters the competition among native species and invasive weeds.this study determines how current and pro-jected N deposition affect the growth,the intraspecific and interspe-cific competitive ability of native and invasive plants in calcareous soils with low P availability.Methods A controlled greenhouse experiment was conducted using spar-ingly soluble hydroxyapatite(HAP)to simulate the calcareous soils with low P availability.the growth and competitive intensity be-tween an invasive weed(Solidago canadensis)and a native weed(Pterocypsela laciniata)exposed to two levels of N addition repre-sentative of current and future N deposition in china were experi-mentally determined.Important Findings P acquisition and the growth of both S.canadensis and P.laciniata growing alone significantly increased with increasing N level.However,the effect of N addition was reduced when intraspecific or interspecific competition existed.N addition altered the com-petitive relationship between S.canadensis and P.laciniata allowing S.canadensis to out-compete P.laciniata due to variation in P ac-quisition from HAP.Elevated N deposition might assist the invasion of S.canadensis in the widely distributed calcareous soils under environmental changes.

ECOLOGICAL EFFECTS OF NITROGEN DEPOSITION ON URBAN FORESTS: AN OVERVIEW

The global urban area is expanding continuously,resulting in unprecedented emissions and deposition of reactive nitrogen(N)in urban environments.However,large knowledge gaps remain in the ecological effects of N deposition on urban forests that provide key ecosystem services for an increasing majority of city dwellers.The current understanding of the spatial patterns and ecological effects of N deposition in urban forests was synthesized based on a literature review of observational and experimental studies.Nitrogen deposition generally increases closer to cities,resulting in an urban hotspot phenomenon.Chemical components of N deposition also shift across urban-suburban-rural gradients,showing higher ratios of ammonium to nitrate in and around urban areas.The ecological effects of N deposition on urban forest ecosystems are overviewed with a special focus on ecosystem N cycling,soil acidification,nutrient imbalances,soil greenhouse gas emissions,tree growth and forest productivity,and plant and soil microbial diversity.The distinct effects of unprecedented N deposition on urban forests are discussed in comparison with the common effects in natural forests.Despite the existing research efforts,several key research needs are highlighted to fill the knowledge gaps in the ecological effects of N deposition on urban forests.

Relationship between dietary amino acid release kinetics and nitrogen deposition in growing pigs

Although the protein content of swine diets is formulated based on the ileal digestibility of protein and amino acids(AA)under current nutrition requirements,the nitrogen utilization efficiency of swine varies based on protein source,which may be related to AA release kinetics.In this experiment,a 2×2 factorial arrangement with casein(CAS)-enriched or corn gluten meal(CGM)-enriched protein sources at different digestible crude protein levels(normal[N],13%;and low[L],11%)were applied to 24 crossbred(DurocLandraceYorkshire)growing pigs(average body weight=43.3±3.5 kg)in 4 treatments(N.CAS,L.CAS,N.CGM,L.CGM,respectively)to investigate the effects of AA release kinetics on nitrogen deposition in growing pigs.Standardized ileal digestible AA in all diets were balanced by adding individual AA to meet the nutrient requirements.The AA release kinetics were detected in vitro by measuring the hydrolysis of various protein diets under pepsin and trypsin conditions.The results demonstrated that the time of AA release peak in the CGM diet was 12 h later than that in the CAS diet.The synchronization indices of dietary AA release in N.CAS,N.CGM,L.CAS,and L.CGM were 23.73%,29.37%,23.40%,and 26.07%,respectively.The N.CGM had the poorest AA release synchronism while the N.CAS had the greatest among the 4 diets.However,within the pigs,L.CAS and N.CGM showed the highest(81.08%)and lowest(73.54%)nitrogen biological values,respectively,despite the standard ileal digestible AA levels being equal for all diets.These results indicate that the release kinetics of dietary AA had great effect on nitrogen deposition.To optimize nitrogen deposition,AA release kinetics and composition should be taken into consideration when formulating diets for growing pigs.

Increased microbial sequestration of soil organic carbon under nitrogen deposition over China’s terrestrial ecosystems

Background:China’s terrestrial ecosystems have been receiving increasing amounts of reactive nitrogen(N)over recent decades.External N inputs profoundly change microbially mediated soil carbon(C)dynamics,but how elevated N affects the soil organic C that is derived from microbial residues is not fully understood.Here,we evaluated the changes in soil microbial necromass C under N addition at 11 forest,grassland,and cropland sites over China’s terrestrial ecosystems through a meta-analysis based on available data from published articles.Results:Microbial necromass C accounted for an average of 49.5%of the total soil organic C across the studied sites,with higher values observed in croplands(53.0%)and lower values in forests(38.6%).Microbial necromass C was significantly increased by 9.5%after N addition,regardless of N forms,with greater stimulation observed for fungal(+11.2%)than bacterial(+4.5%)necromass C.This increase in microbial necromass C under elevated N was greater under longer experimental periods but showed little variation among different N application rates.The stimulation of soil microbial necromass C under elevated N was proportional to the change in soil organic C.Conclusions:The stimulation of microbial residues after biomass turnover is an important pathway for the observed increase in soil organic C under N deposition across China’s terrestrial ecosystems.

Are typhoon and marine eutrophication the possible missing sources of high dissolved organic nitrogen in wet deposition?

The aim of this study is to elaborate a possible missing source of high-throughput organic nitrogen in rainfall.The authors classified the observed flux data of dissolved organic nitrogen in terms of the attributes of the wet deposition event itself,such as the season,precipitation,air mass backward trajectory,and effect of typhoons.The monitoring results of the ocean eutrophication and the chlorophyll-a map of the surface water were compared with the trajectory of the high-flux deposition events.The results show that approximately one third of the total wet deposition organic nitrogen derived from a confluence of three factors:rain in the wet season,air masses from the ocean,and rainfall over 50 mm.It could be seen that the co-occurrence of intense events such as a typhoon and eutrophic surface sea waters might be an important source of dissolved organic nitrogen in wet deposition.