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The impacts of nitrogen on environmental quality, greenhouse gas balances, ecosystem and biodiversity in China are of great concern given the magnitude of demand for food and energy. Comprehensive summaries of historic N flows and their critical threats and sustainable management are urgently needed. This paper initially reviews the historical trends of N flows in China and identifies the critical threats of N loss. Subsequently, it describes some recent success stories of N management, and finally indicates barriers to N pollution control. This review highlights three key points. Firstly, a steady increase of N input in China has led to a series of environmental problems via leaching and runoff, ammonia emissions and denitrification. Secondly, although great efforts to improve N management and N safety in China, further quantifications of N flows and analysis of their underlying mechanisms are needed to improve the understanding of the N cycle and pollution control. Finally, it proposes that the best available technologies combined with regulatory plans, laws, projects and policies should be implemented to overcome current barriers in N control and achieve a balance between the sustainable use of N resources and environmental conservation in China. [ABSTRACT FROM AUTHOR]

This paper determined the fixed-ammonium (NH4*) contents of lamprophyres in the Zhenyuan gold orefield, Yunnan Province, China. The results show that the NH4* contents of minettes in the orefield range from 120 x 10-6 to 469 x 10-6 and those of kersantites from 74. 3 X 10-6 to 136 X 10-6. These values are higher than those of other mantle-derived rocks (less than 50 X 10-6) , but lower than those of carbonaceous wall rocks in the orefield (from 1200 x 10-6 to 1343 X 10-6). Combining with the Sr isotopic composition, this paper suggested that lamprophyres in the orefield with high NH4* contents relative to other mantle-derived rocks would not have resulted from the primary magma contaminated by crustal materials in the process of rising or in the magma chamber, but from mantle metasomatism. [ABSTRACT FROM AUTHOR]

Aquatic ecosystems occasionally show ecological thresholds, defined as the point at which there is a sudden shift in production, trait or biomass or where changes in an environmental driver create nonlinear responses at the ecosystem level. Previous studies of lakes have mainly focused on how reduction in particularly phosphorus (P) concentrations helps to create a shift in lakes from a turbid to a clear state (re-oligotrophication), whereas the effect of nitrogen (N) reduction is less well studied. Here, by analysing a 28-year monthly monitoring dataset (from December 1991 to November 2019) from the subtropical, large eutrophic Lake Taihu, China, we identified a sudden shift in phytoplankton biomass and composition that coincided with a pronounced change in ecosystem functions, for example, resource use efficiency (RUE), during a period with reduction of the external nutrient loading. The changes were particularly strong in winter–spring where a sudden decrease in N concentrations was accompanied by a sudden increase in diatom biomass and phytoplankton RUE and a shift from green algae and flagellate co-dominance to dominance of diatoms. Structural equation modelling further indicated that ammonium reduction led directly to increases in winter–spring phytoplankton RUE and diatom biomass. Repeated fish stocking likely also contributed to the changes in biomass and RUE. Our study provides new insight into the ecological responses to N loading reduction and contributes to the understanding of lake responses to early re-oligotrophication, which was pronounced mainly in the colder seasons in subtropical Lake Taihu, similar to findings in the early phase of re-oligotrophication in numerous temperate lakes. [ABSTRACT FROM AUTHOR]

To evaluate the effects of application of biochar and straw return for consecutive years on N2O emissions and crop yields in North China, a three-year field experiment of applying biochar and straw following a ten-year application was conducted in a wheat–maize rotation system. Four treatments were set up, including F (NPK fertilizer only); FB (NPK fertilizer + 9.0 t·ha−1 biochar); FS (NPK fertilizer + straw); and FSB ((NPK fertilizer + 9.0 t·ha−1 biochar combined with straw). The results showed that compared with the F treatment, the FB treatment significantly reduced soil N2O emissions by 20.2%, while the FS and FSB treatments increased it by 23.7% and 41.4%, respectively. The FB treatment reduced soil N2O emissions by 15.1% in the wheat season and 23.2% in the maize season, respectively. The FS and FSB treatments increased the N2O emissions by 20.7% and 36.7% in the wheat season, respectively, and by 25.5% and 44.2% in the maize season, respectively. In the wheat season, the soil water content (SWC), NO3−-N content and pH were the main influencing factors of the soil N2O emissions. In the maize season, SWC and NO3−-N content were the main influencing factors. In addition, the FB, FS and FSB treatments increased the crop yield by 4.99%, 8.40% and 10.25% compared with the F treatment, respectively. In conclusion, consecutive application of biochar can significantly reduce N2O emissions and improve crop yield. Although FS and FSB treatments can also improve the crop yield, they are not beneficial to suppressing N2O emissions. Therefore, the successive application of biochar is an effective measure to reduce N2O emissions and maintain crop yield. [ABSTRACT FROM AUTHOR]

Introduction: An aerobic denitrifier was isolated from the Hua-Jia-Chi pond in China and identified as Pseudomonas mendocina 3-7 (Genbank No. HQ285879). This isolated strain could express periplasmic nitrate reductase which is essential for aerobic denitrification occurred when the dissolved oxygen (DO) level maintains at 3-10 mg L. Methods: To determine whether the ability of isolated strain is exhibited in the bioremediation of polluted drinking source water, the heterotrophic nitrification and aerobic denitrification characteristics of P. mendocina 3-7 under different cultural conditions such as oxygen level, nitrate and organic concentrations were studied from the nitrogenous balance in the paper. Results and conclusions: By measuring the nitrogen balance in all experiments under different culture conditions, the removal of total organic carbon and ammonium was positively correlated with total nitrogen removal, especially under high substrate level. With substrate concentration decreasing, ammonium and nitrate removal occurred separately, and ammonium was completely utilized first under low substrate concentration. Compared to that under high substrate level, the specific growth rate of P. mendocina 3-7 was not low under the low substrate level and the pollutant removal efficiencies remained high, which implies the stronger nitrogen removal and acclimatization capacities of the strain in oligotrophic niches. [ABSTRACT FROM AUTHOR]

Erythropalum scandens Bl. is a woody vegetable with high nitrogen demand that inhabits southern China. Ammonium and nitrate are the two main forms of inorganic nitrogen that plants directly absorb. A pot experiment was performed to determine the growth, physiological responses, and preferences of 12-month-old E. scandens seedlings for ammonium and nitrate. Aboveground and underground growth indexes, biomass, physiological and biochemical indexes (chlorophyll [Chl], soluble sugar, soluble protein and free proline contents), and substrate pH and nitrogen contents were determined under different nitrate and ammonium ratios (0 NO3-: 100 NH4+, 25 NO3-: 75 NH4+, 50 NO3-: 50 NH4+, 75 NO3-: 25 NH4+, and 100 NO3-: 0 NH4+), and the control (0 NO3-: 0 NH4+). The results showed that ammonium and nitrate improved the growth and physiological status of E. scandens seedlings in most of the treatments compared to the control. The aboveground growth status and biomass accumulation of E. scandens seedlings were significantly better under the 0 NO3-: 100 NH4+ treatment during fertilization compared with all other treatments. However, the growth status of the underground parts was not significantly different among treatments. Significant differences in osmoregulator content, except for soluble sugars, and Chl content were observed. Soluble sugars and soluble proteins were highest under the 0 NO3-: 100 NH4+ treatment at the end of fertilization (day 175). However, free proline accumulated during fertilization and the increase in NO3- indicated that excessive use of NO3- had a negative effect on the E. scandens seedlings. The order of accumulating nitrogen content was leaves > roots > stems. The highest N accumulation occurred in the aboveground parts under the 0 NO3-: 100 NH4+ treatment, whereas the highest N accumulation occurred in the underground parts under the 50 NO3-: 50 NH4+ treatment. Substrate pH increased at the end of fertilization (day 175) compared with the middle stage (day 75), while total nitrogen, ammonium, and nitrate were highly significantly different among the treatments. Total nitrogen and NH4+ content were the highest under the 0 NO3-: 100 NH4+ treatment, while NO3- content was the highest under the 100 NO3-: 0 NH4+ treatment. In conclusion, 12-month-old E. scandens seedlings grew best, and had better physiological conditions in NH4+ than NO3-. The 0 NO3-:100 NH4+ treatment (ammonium chloride 3.82 g/plant) resulted in the best growth and physiological conditions. Most of the growth and physiological indexes were inhibited with the increase in nitrate. [ABSTRACT FROM AUTHOR]

Nitrogen (N) is an essential nutrient that plants require and is, most of the time, limited in different terrestrial ecosystems. Forming symbioses with plants, arbuscular mycorrhizal (AM) fungi improve mineral element uptake and the net primary production of plants. Recent reports have suggested that AM fungi mediate N uptake in plants. However, there are fewer studies on the influence of AM fungi on the response of Lycium barbarum, a medicinal plant in northwest China, under different N-addition conditions. In this study, the effect of Rhizophagus irregularis, N forms (NO3− and NH4+), and N levels (1.5, 7.5, 15, 30 mM) on the performance of L. barbarum was evaluated through a pot experiment. The application of R. irregularis significantly improved L. barbarum biomass, net photosynthetic rate, and root tissue viability under adequate NO3− and NH4+ supplies, and mycorrhizal plants showed better performance under NO3− supply. AM colonization enhanced N acquisition under adequate NO3− supply and strongly induced the expression of LbAMT3-1 in L. barbarum roots. Based on these results, we propose that NO3−-dominated N supply favors mycorrhizal symbiosis to a greater extent than NH4+; this study provides a basis for maintaining beneficial AM symbiosis during nitrogen fertilizer use in arable land. [ABSTRACT FROM AUTHOR]

Purpose: Ammonium and nitrate are the main components of anthropogenic nitrogen (N) from atmosphere, while their ratio varies worldwide. However, it remains unclear whether forest soil ecosystem changes differ when various ratios of mixed N are added. Methods: Ammonium and nitrate were mixed in different ratios (3:7, 4:6, 5:5, 6:4, and 7:3) and forest soils were fertilized for four years. Then, the soil pH, microbial biomass, enzymatic activities, and organic carbon (SOC) were determined. The potential mechanism was analyzed using structural equation modeling. Results: Ammonium addition induced a greater fungal biomass decrease than nitrate addition (-0.618 vs. -0.329). The fungal biomass decrease further led to a decline in degradation enzymes, which resulted in SOC accumulation. Phosphatase activity increased and correlated with C-degrading enzymatic activities after N addition, indicating that phosphorous may become the limiting factor that controls degradation. Both ammonium and nitrate addition caused soil acidification (P < 0.05), but the acidification did not affect the enzymatic activities (P > 0.05). Moreover, when the added mixed N component ratios were closer to the ambient N component ratios, fewer changes in soil microbial biomass, enzymatic activities, and SOC were observed. This can be explained by the home-field advantage, because soil microbes may have adapted more readily to the ambient N components of the sample site and display fewer responses when the added N is nearly similar to the ambient N types. Conclusion: When designing N addition field experiments, the type of N compounds should be considered, besides the amount and duration. [ABSTRACT FROM AUTHOR]

Abstract: Monthly nitrogen isotopes of ammonium and nitrate in wet deposition in the city of Guangzhou, and the causes of their variability, are reported in this paper. Nitrate δ15N showed nearly constant values around zero in the dry season (October to April), but oscillating values from negative to positive in the rainy season (May to September). By contrast, ammonium δ15N displayed lower values during the rainy season than in the dry season. The rural area north of the city was considered as the prominent source of ammonium and nitrate in spring and early summer (May and June), as suggested by their concurrent negative isotopic trends and higher NH4 +/NO3 − ratios. From July to September, different dominating sources from the city, i.e., fossil fuel combustion for nitrate, and sewage and waste emission for ammonium, caused disparate δ15N trends of the two species, showing positive nitrate δ15N, but still negative ammonium δ15N. During the cool dry season, the high values of ammonium δ15N and concurrently low NH4 +/NO3 − ratios suggested the decrease in NH3 volatilization and relatively important thermogenic origin of ammonium, but the intermediate nitrate δ15N values around zero may be a result of a balanced emission of NOx from the city and the rural areas. The isotopic effects of chemical conversion of NOx to nitrate and washout of nitrate were ruled out as significant causes of nitrate δ15N variability, but ammonium washout, during which 15N is assumed to be preferentially removed, may partly contribute to the ammonium δ15N variability. [Copyright &y& Elsevier]

Anthropogenic nitrogen (N) emissions and deposition have been increasing over past decades. However, spatiotemporal variations of N deposition levels and major sources remain unclear in many regions, which hinders making strategies of emission mitigation and evaluating effects of elevated N deposition. By investigating moss N contents and δ15N values in southwestern (SW) China in 1954–1964, 1970–1994, and 2005–2015, we reconstructed fluxes and source contributions of atmospheric ammonium (NH4+) and nitrate (NO3‐) deposition and evaluated their historical changes. For urban and non‐urban sites, averaged moss N contents did not differ between 1954–1964 and 1970–1994 (1.2%–1.3%) but increased distinctly in 2005–2015 (1.6%–2.3%), and averaged moss δ15N values decreased from +0.4‰ to +3.3‰ in 1954–1964 to −1.9‰ to −0.7‰ in 1974–1990, and to −4.8‰ to −3.6‰ in 2005–2015. Based on quantitative estimations, N deposition levels from the 1950s to the 2000s did not change in the earlier 20 years but were elevated substantially in the later 30 years. Moreover, the elevation of NH4+ deposition (by 12.2 kg‐N/ha/year at urban sites and 4.6 kg‐N/ha/year at non‐urban sties) was higher than that of NO3‐ deposition (by 6.0 and 2.9 kg‐N/ha/year, respectively) in the later 30 years. This caused a shifted dominance from NO3‐ to NH4+ in N deposition. Based on isotope source apportionments, contributions of combustion‐related NH3 sources (vehicle exhausts, coal combustion, and biomass burning) to the elevation of NH4+ deposition were two times higher than volatilization NH3 sources (wastes and fertilizers) in the later 30 years. Meanwhile, non‐fossil fuel NOx sources (biomass burning, microbial N cycles) contributed generally more than fossil fuel NOx sources (vehicle exhausts and coal combustion) to the elevation of NO3‐ deposition. These results revealed significant contributions of combustion‐related NH3 and non‐fossil fuel NOx emissions to the historical elevation of N deposition in SW China, which is useful for emission mitigation and ecological effect evaluation of atmospheric N loading. [ABSTRACT FROM AUTHOR]

Many studies have recently been done on understanding the sources and formation mechanisms of atmospheric aerosols at ground level. However, vertical profiles and sources of size-resolved particulate matter within the urban boundary layer are still lacking. In this study, vertical distribution characteristics of size-segregated particles were investigated at three observation platforms (ground level, 118 m, and 488 m) on the 610 m high Canton Tower in Guangzhou, China. Size-segregated aerosol samples were simultaneously collected at the three levels in autumn and winter. Major aerosol components, including water-soluble ions, organic carbon, and elemental carbon, were measured. The results showed that daily average fine-particle concentrations generally decreased with height. Concentrations of sulfate and ammonium in fine particles displayed shallow vertical gradients, and nitrate concentrations increased with height in autumn, while the chemical components showed greater variations in winter than in autumn. The size distributions of sulfate and ammonium in both seasons were characterized by a dominant unimodal mode with peaks in the size range of 0.44–1.0 µ m. In autumn, the nitrate size distribution was bimodal, peaking at 0.44–1.0 and 2.5–10 µ m, while in winter it was unimodal, implying that the formation mechanisms for nitrate particles were different in the two seasons. Our results suggest that the majority of the sulfate and nitrate is formed from aqueous-phase reactions, and we attribute coarse-mode nitrate formation at the measurement site to the heterogeneous reactions of gaseous nitric acid on existing sea-derived coarse particles in autumn. Case studies further showed that atmospheric aqueous-phase and heterogeneous reactions could be important mechanisms for sulfate and nitrate formation, which, in combination with adverse weather conditions such as temperature inversion and calm wind, led to haze formation during autumn and winter in the Pearl River Delta (PRD) region. [ABSTRACT FROM AUTHOR]

Excessive nitrogen (N) deposition can impact lichen diversity in forest ecosystems, and this is a particular situation in China. Here, we examined the N uptake, assimilation, and the impact of excessive N deposition on the symbiotic balance of dominant epiphytic lichens in the subtropical forests in the Mts. Shennongjia of central China. The results show that lichen species took up, assimilated and utilized more ammonium than nitrate in a species‐specific way, following the increase of N availability. The photobiont of the lichens decreased with the increase of N concentration following an initial increase, while the mycobiont response to the N addition was not apparent. Considerable variation in response to excessive N deposition exists among the lichen species. Usnea longissima could regulate its N uptake, resulting in a stable photobiont‐mycobiont ratio among N treatments. In contrast, the photobiont‐mycobiont ratio of other four lichens increased initially but decreased when N concentration exceeded a certain level, and N stress may have broken the balance between photobiont and mycobiont of these lichens. Our results suggest that most epiphytic lichens in subtropical forest of central China could uptake and assimilate more ammonium than nitrate and that the balance between photobiont and mycobiont of many epiphytic lichens might change with the increasing N deposition load, which could impact the lichen diversity of this forest ecosystem. [ABSTRACT FROM AUTHOR]

Particulate matter (PM) pollution is a severe environmental problem in the Beijing–Tianjin–Hebei (BTH) region in North China. PM studies have been conducted extensively in Beijing, but the chemical composition, sources, and atmospheric processes of PM are still relatively less known in nearby Tianjin and Hebei. In this study, fine PM in urban Shijiazhuang (the capital of Hebei Province) was characterized using an Aerodyne quadrupole aerosol chemical speciation monitor (Q-ACSM) from 11 January to 18 February in 2014. The average mass concentration of non-refractory submicron PM (diameter <1 µm , NR-PM 1) was 178±101 µgm-3 , and it was composed of 50 % organic aerosol (OA), 21 % sulfate, 12 % nitrate, 11 % ammonium, and 6 % chloride. Using the multilinear engine (ME-2) receptor model, five OA sources were identified and quantified, including hydrocarbon-like OA from vehicle emissions (HOA, 13 %), cooking OA (COA, 16 %), biomass burning OA (BBOA, 17 %), coal combustion OA (CCOA, 27 %), and oxygenated OA (OOA, 27 %). We found that secondary formation contributed substantially to PM in episodic events, whereas primary emissions were dominant (most significant) on average. The episodic events with the highest NR-PM 1 mass range of 300–360 µgm-3 were comprised of 55 % of secondary species. On the contrary, a campaign-average low OOA fraction (27 %) in OA indicated the importance of primary emissions, and a low sulfur oxidation degree (FSO4) of 0.18 even at RH >90 % hinted at insufficient oxidation. These results suggested that in Shijiazhuang in wintertime fine PM was mostly from primary emissions without sufficient atmospheric aging, indicating opportunities for air quality improvement by mitigating direct emissions. In addition, secondary inorganic and organic (OOA) species dominated in pollution events with high-RH conditions, most likely due to enhanced aqueous-phase chemistry, whereas primary organic aerosol (POA) dominated in pollution events with low-RH and stagnant conditions. These results also highlighted the importance of meteorological conditions for PM pollution in this highly polluted city in North China. [ABSTRACT FROM AUTHOR]

Five-year (2011-2015) measurements of gaseous NH3, NO2, and HNO3 and particulate NH4+ and NO3- in air and/or precipitation were conducted at 27 sites in the Nationwide Nitrogen Deposition Monitoring Network (NNDMN) to better understand spatial and temporal (seasonal and annual) characteristics of reactive nitrogen (Nr) concentrations and deposition in eastern China. Our observations reveal annual average concentrations (16.4-32.6 µgN m-3), dry deposition fluxes (15.8-31.7 kg N ha-1 yr-1), and wet/bulk deposition fluxes (18.4-28.0 kg N ha-1 yr-1) based on land use, ranked as urban > rural > background sites. Annual concentrations and dry deposition fluxes of each Nr species in air were comparable at urban and background sites in northern and southern regions, but were significantly higher at northern rural sites. These results, together with good agreement between spatial distributions of NH3 and NO2 concentrations determined from ground measurements and satellite observations, demonstrate that atmospheric Nr pollution is heavier in the northern region than in the southern region. No significant inter-annual trends were found in the annual Nr dry and wet/bulk N deposition at almost all of the selected sites. A lack of significant changes in annual averages between the 2013-2015 and 2011-2012 periods for all land use types suggests that any effects of current emission controls are not yet apparent in Nr pollution and deposition in the region. Ambient concentrations of total Nr exhibited non-significant seasonal variation at all land use types, although significant seasonal variations were found for individual Nr species (e.g. NH3, NO2, and pNO3-) in most cases. In contrast, dry deposition of total Nr exhibited a consistent and significant seasonal variation at all land use types, with the highest fluxes in summer and the lowest in winter. Based on sensitivity tests by the GEOS-Chem model, we found that NH3 emissions from fertilizer use (including chemical and organic fertilizers) were the largest contributor (36 %) to total inorganic Nr deposition over eastern China. Our results not only improve the understanding of spatial--temporal variations of Nr concentrations and deposition in this pollution hotspot, but also provide useful information for policy-makers that mitigation of NH3 emissions should be a priority to tackle serious N deposition in eastern China. [ABSTRACT FROM AUTHOR]

Asian dust has been reported to carry anthropogenic reactive nitrogen during transport from source areas to the oceans. In this study, we attempted to characterize NH+4 and NO-3 in atmospheric particles collected at a coastal site in northern China during spring dust events from 2008 to 2011. Based on the mass concentrations of NH+4 and NO-3 in each total suspended particle (TSP) sample, the samples can be classified into increasing or decreasing types. In Category 1, the concentrations of NH+4 and NO-3 were 20- 440% higher in dust day samples relative to samples collected immediately before or after a dust event. These concentrations decreased by 10-75% in the dust day samples in Categories 2 and 3. Back trajectory analysis suggested that multiple factors, such as the transport distance prior to the reception site, the mixing layer depth on the transport route and the residence time across highly polluted regions, might affect the concentrations of NH+4 and NO-3. NH+4 in the dust day samples was likely either in the form of ammonium salts existing separately to dust aerosols or as the residual of incomplete reactions between ammonium salts and carbonate salts. NO-3 in the dust day samples was attributed to various formation processes during the long-range transport. The positive matrix factorization (PMF) receptor model results showed that the contribution of soil dust increased from 23 to 36% on dust days, with decreasing contributions from local anthropogenic inputs and associated secondary aerosols. The estimated deposition flux of NNH+4 CNO-3 varied greatly from event to event; e.g., the dry deposition flux of NNH+4 CNO-3 increased by 9-285% in Category 1 but decreased by 46- 73% in Category 2. In Category 3, the average dry deposition fluxes of particulate nitrate and ammonium decreased by 46% and increased by 10 %, respectively, leading to 11- 48% decrease in the fluxes of NNH+4 CNO-3. [ABSTRACT FROM AUTHOR]

The nitrate to ammonium ratios in nitrogen (N) compounds in wet atmospheric deposits have increased over the recent past, which is a cause for some concern as the individual effects of nitrate and ammonium deposition on the biomass of different soil microbial communities and enzyme activities are still poorly defined. We established a field experiment and applied ammonium (NH4Cl) and nitrate (NaNO3/at monthly intervals over a period of 4 years. We collected soil samples from the ammonium and nitrate treatments and control plots in three different seasons, namely spring, summer, and fall, to evaluate the how the biomass of different soil microbial communities and enzyme activities responded to the ammonium (NH4Cl) and nitrate (NaNO3/applications. Our results showed that the total contents of phospholipid fatty acids (PLFAs) decreased by 24 and 11% in the ammonium and nitrate treatments, respectively. The inhibitory effects of ammonium on Gram-positive bacteria (G+) and bacteria, fungi, actinomycetes, and arbuscular mycorrhizal fungi (AMF) PLFA contents ranged from 14 to 40% across the three seasons. We also observed that the absolute activities of C, N, and P hydrolyses and oxidases were inhibited by ammonium and nitrate, but that nitrate had stronger inhibitory effects on the activities of acid phosphatase (AP) than ammonium. The activities of Nacquisition specific enzymes (enzyme activities normalized by total PLFA contents) were about 21 and 43% lower in the ammonium and nitrate treatments than in the control, respectively. However, the activities of P-acquisition specific enzymes were about 19% higher in the ammonium treatment than in the control. Using redundancy analysis (RDA), we found that the measured C, N, and P hydrolysis and polyphenol oxidase (PPO) activities were positively correlated with the soil pH and ammonium contents, but were negatively correlated with the nitrate contents. The PLFA biomarker contents were positively correlated with soil pH, soil organic carbon (SOC), and total N contents, but were negatively correlated with the ammonium contents. The soil enzyme activities varied seasonally, and were highest in March and lowest in October. In contrast, the contents of the microbial PLFA biomarkers were higher in October than in March and June. Ammonium may inhibit the contents of PLFA biomarkers more strongly than nitrate because of acidification. This study has provided useful information about the effects of ammonium and nitrate on soil microbial communities and enzyme activities. [ABSTRACT FROM AUTHOR]

Nitrogen contamination is a global concern and has been a serious problem in agricultural areas. The present study was carried out in an intensively irrigated region of northwest China along the New Silk Road, Yinchuan Plain, where the residents depend on the groundwater as the primary source for drinking. To understand the nitrogen contamination in the aquifer system, the distribution of nitrate and ammonium and its controlling factors were studied based on hydrochemical, hydrogeological, and isotopic analyses. 11.37 and 40% of phreatic water samples are categorized as NO-N and NH-N pollution in accordance with the WHO standards. A total of 59.52% of confined water samples has high NH-N values, exceeding the permissible limit for drinking purpose. The results indicate NO-N predominates in the shallow water and NH-N predominates in the deep water for the single phreatic aquifer. For the multilayer structure area, NO-N predominates in the phreatic aquifer of the western and the southern parts of the plain; NH-N predominates in the phreatic aquifer of the middle and the northern parts of the plain, and in the confined aquifers where groundwater pumping had been performed. The mixture of synthetic fertilizer and manure/sewage is primarily responsible for the phreatic water based on isotopic analysis. In the confined aquifers, higher NH-N concentrations are mainly attributed to intensive pumping under higher pumping rates. The results of this study can be used as a scientific basis for the future research on nitrogen in the plain. They can also be used by scholars and decision makers who are interested in groundwater protection and sustainable development. [ABSTRACT FROM AUTHOR]

High nitrogen (N) concentrations in rural domestic water supplies have been attributed to excessive agricultural N leaching into shallow groundwater systems; therefore, it is important to determine the impact of agriculture (e.g., rice production) on groundwater quality. To understand the impact of agricultural land use on the N concentrations in the shallow groundwater in subtropical central China, a large observation program was established to observe ammonium-N (NH-N), nitrate-N (NO-N), and total N (TN) concentrations in 161 groundwater observation wells from April 2010 to November 2012. The results indicated that the median values of NH-N, NO-N, and TN concentrations in the groundwater were 0.15, 0.39, and 1.38 mg N L, respectively. A total of 36.3 % of the water samples were categorized as NH-N pollution, and only a small portion of the samples were categorized as NO-N pollution, based on the Chinese Environmental Quality Standards for Groundwater of GB/T 14848-93 (General Administration of Quality Supervision of China, ). These results indicated of moderate groundwater NH-N pollution, which was mainly attributed to intensive rice agriculture with great N fertilizer application rates in the catchment. In addition, tea and vegetable fields showed higher groundwater NO-N and TN concentrations than other agricultural land use types. The factorial correspondence analysis (FCA) suggested that the flooded agricultural land use types (e.g., single-rice and double-rice) had potential to impose NH-N pollution, particularly in the soil exhausting season during from July to October. And, the great N fertilizer application rates could lead to a worse NO-N and TN pollution in shallow groundwater. Hence, to protect groundwater quality and minimize NH-N pollution, managing optimal fertilizer application and applying appropriate agricultural land use types should be implemented in the region. [ABSTRACT FROM AUTHOR]

The authors analyze the sensitivities of source regions in East Asia to PM2.5(particulate matter with an aerodynamic diameter of ≤2.5 µm) concentration at Fukue Island located in the western part of Japan by using a regional chemical transport model with emission sensitivity simulations for the year 2010. The temporal variations in PM2.5concentration are generally reproduced, but the absolute concentration is underestimated by the model. Chemical composition of PM2.5in the model is compared with filter sampling data in spring; simulated sulfate, ammonium, and elemental carbon are consistent with observations, but mass concentration of particulate organic matters is underestimated. The relative contribution from each source region shows the seasonal variation, especially in summer. The contribution from central north China (105°E–124°E, 34°N–42°N) accounts for 50–60% of PM2.5at Fukue Island except in summer; it significantly decreases in summer (18%). Central south China (105°E–123°E, 26°N–34°N) has the relative contribution of 15–30%. The contribution from the Korean Peninsula is estimated at about 10% except in summer. The domestic contribution accounts for about 7% in spring and autumn and increases to 19% in summer. We also estimate the relative contribution to daily average concentration in high PM2.5days (>35 μg m−3). Central north China has a significant contribution of 60–70% except in summer. The relative contribution from central south China is estimated at 46% in summer and about 30% in the other seasons. The contributions from central north and south China on high PM2.5days are generally larger than those of their seasonal mean contributions. The domestic contribution is smaller than the seasonal mean value in every season; it is less than 10% even in summer. These model results suggest that foreign anthropogenic sources have a substantial impact on attainment of the atmospheric environmental standard of Japan at Fukue Island.Implications: The contribution from several source regions in East Asia to PM2.5 concentration at Fukue Island, a remote island located in the western part of Japan and close to the Asian continent, is estimated using a three-dimensional chemical transport model. The model results suggest that PM2.5 that is attributed to foreign anthropogenic sources have a larger contribution than that of domestic pollution and have a substantial impact on attainment of the atmospheric environmental standard of Japan at Fukue Island. [ABSTRACT FROM AUTHOR]

Soil ammonia oxidizers play a critical role in nitrogen cycling and ecological restoration. The composition and structure of soil ammonia oxidizers and their impacting factors were studied in four typical ecosystem soils, tussock (T), shrub (S), secondary forest (SF), and primary forest (PF), during vegetation restoration in the Karst region of Southwest China. The composition and structure of the ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) communities were characterized by sequencing the amoA and arch- amoA genes, respectively. The diversity of soil ammonia oxidizers (except in S) and plant Shannon diversity index gradually increased with vegetation restoration, and the ammonia oxidizer communities differed significantly ( p < 0.001). Amplicons of AOA from the Nitrososphaera cluster dominated all four ecosystem soils. AOB Nitrosospira cluster 3b only appeared in PF and SF soils, while Nitrosospira cluster 3a species were found in all soils. Changes in AOB paralleled the changes in soil ammonium content that occurred with vegetation restoration. Redundancy analysis showed that the distribution of dominant AOB species was linked to pH, soil urease activity, and soil C/N ratio, whereas the distribution of dominant AOA species was mainly influenced by litter nitrogen content and C/N ratio. These results suggested that the composition and structure of the AOB community were more sensitive to changes in vegetation and soil ammonium content, and may be an important indicator of nitrogen availability in Karst ecosystem soils. [ABSTRACT FROM AUTHOR]

Spatial and temporal distribution characteristics of total nitrogen and ammonium nitrogen in the sediments, pore water and overlying water of Xiangxi Bay in China Three- Gorge Reservoir were investigated. In surveys, the sampling was undertaken from six sites of Xiangxi Bay on three dates: 29 March 2009, 28 March 2010 and 17 August 2010. Mean values of total nitrogen and ammonium nitrogen contents in the sediments and pore water of Xiangxi Bay all increased with time, especially in summer. There were intimate relationships between internal nitrogen loading and water ecosystem. Correlation coefficients R were 0.7408 (between total nitrogen in pore water and total nitrogen in sediments) and 0.7483 (between total nitrogen in sediments and chlorophyll- a in surface water), respectively. Total nitrogen concentration differences between pore water and overlying water were all positive and had good correlation with chlorophyll- a concentration of Xiangxi Bay. The release of nitrogen in sediments had an important impact on phytoplankton growth in Xiangxi Bay. [ABSTRACT FROM AUTHOR]

An improved Gas and Aerosol Collector (GAC) equipped with a newly designed aerosol collector and a set of dull-polished wet annular denuder (WAD) was developed based on a Steam Jet Aerosol Collector (SJAC) sampler. Combined with Ion Chromatography (IC) the new sampler performed well in laboratory tests with high collection efficiencies for SO2 (above 98%) and particulate sulfate (as high as 99.5%). An inter-comparison between the GAC-IC sys- tem and the filter-pack method was performed and the results indicated that the GAC-IC system could supply reliable particulate sulfate, nitrate, chloride, and ammonium data in field measurement with a much wider range of ambient concentrations. When applied in two major field campaigns (rural and coastal sites) in China, the GAC-IC system provided high- quality data in ambient conditions even under high loadings of pollutants. Its measurements were highly correlated with data by other commercial instruments such as the SO2 analyzer (43c, Thermo-Fisher, USA; R² as 0.96), the HONO analyzer (LOPAP, Germany; R² as 0.91 for samples from 15:00 to 07:00), a filter sampler (Tianhong, China; R² as 0.86 for SO42-), and Aerosol Mass Spectrometer (AMS, Aerodyne, USA; R² above 0.77 for major species) over a wide range of concentrations. Through the application of the GAC-IC system, it was identified that 70% of chloride and nitrate by the filter method could be lost during daytime sampling due to high temperature in the rural site of Kaiping. In Changdao field campaign (coastal site), though a particle dryer was applied, its drying efficiency was not well considered for the collection efficiency of AMS seemed still interfered a bit by local high relative humidity. If the interomparison was done with relative humidity below 50%, the correlations ranged from 0.81 to 0.94 for major species. Through laboratory and field studies, this instrument is proved particularly useful in future intensive campaigns or long-term monitoring stations to study various environmental issues such as secondary aerosol and haze formation, as well as climate change. [ABSTRACT FROM AUTHOR]

Generally, the foliar sheaths of seagrass contribute a large biomass to the dry weight of plants, and are found to be above-sediment biomass or, sometimes, below-sediment biomass. However, the role of foliar sheaths of seagrass in nutrient uptake has not yet been established. Thus, this study was performed to test whether the growth form of foliar sheaths affects the nutrient uptake properties of the seagrass. Two separate sets of morphotypes of the seagrass Thalassia hemprichii were collected from two different tropical meadows in coastal Hainan Island, China in the South China Sea. Ammonium (NH) and phosphate (P) uptake by solely blades and roots (experiment I), and above and below-sediment tissues (experiment II) of the two sets of specimens were examined in partitioned chambers using laboratory incubations. Curve profiles of the blade and root saturation uptake kinetics were shown to be similar for the two morphotypes of T. hemprichii. However, the above and below-sediment tissues uptake kinetics had different characteristics between the two morphotypes. For plants with above-sediment foliar sheaths, uptake by the above-sediment tissues contributed an important part of the whole plants' nutrient acquisition. In contrast, for plants with below-sediment foliar sheaths, the contribution of nutrient uptake by above-sediment foliar blade tissues seemed almost negligible. Therefore, the results demonstrated that foliar sheaths of the tropical seagrass T. hemprichii were able to absorb NH and P. Especially interesting is that the capacity for uptake by robust foliar sheaths growing beneath the sediment was remarkable (we termed this the Zhang-Huang-Thorhaug effect). The role of sheaths in nutrient acquisition found in this study is critical in elucidating seagrass nutrient uptake strategies. [ABSTRACT FROM AUTHOR]

Based on PM2.5 chemical data sets from literature and from our surface observations, chemical species and reconstructed speciation of PM2.5 in representative Chinese megacities and across China were compared to draw insights into the characteristics of PM2.5 speciation. PM2.5 mass concentrations and speciation compositions varied substantially over geographical regions in China. Near six-fold variations in average PM2.5 concentrations (34.0-193.4 μgm-3) across China were found with high PM2.5 levels (> 100 μg m-3) appearing in the cities in the northern and western regions and low levels (<40 μg m-3) in the remote forest area (Changbai Mountain) and in Hong Kong. The percentages of the sum of sulfate, nitrate and ammonium, organic matter, crustal material, and elemental carbon in PM2.5 mass ranged 7.1-57%, 17.7-53 %, 7.1-43 %, and 1.3-12.8%, respectively. At both urban and rural sites in the eastern region, the sum of sulfate, nitrate and ammonia typically constituted much higher fractions (40-57%) of PM2.5 mass, indicative of more local formation/production and regional transport of the secondary aerosols, thus more intensive characteristic of "complex atmospheric pollution" compared to the western region. Organic matter had significant contribution to PM2.5 over all the sites. Organic matter plus sulfate, nitrate, and ammonia accounted for 53-90% of PM2.5 mass across China. PM2.5 speciation across China was also characterized by high content of crustal material, which was usually at more than ~10 ugm-3 level or shared ~ 10 % of PM2.5 mass in urban areas, due to transported desert dust and locally induced dust. In four representative megacities (i.e. Beijing, Chongqing, Shanghai, and Guangzhou), PM2.5 mass and major components (except sulfate) were at higher levels than those in US continental east by one order of magnitude. Distinct differences in nitrate and sulfate levels and their mass ratio Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed imply that mobile sources are likely more important in Guangzhou, whereas in Chongqing it is stationary (coal combustion) sources. The observed intra-city variations in PM2.5 mass and speciation indicate that both local emissions and regional transportation contributed significantly to high fine particle loadings in Beijing, while local contribution likely played a predominant role in Chongqing. During the ten-year period from 1999 through 2008 in urban Beijing, both the sum of sulfate, nitrate, and ammonia and Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed ratio exhibited steadily increasing trends, implying that the characteristic of "complex atmospheric pollution" and the contribution from mobile sources were being enhanced. [ABSTRACT FROM AUTHOR]

ording to the transport theory of soil solutes and the conditions of soil, geology and climate in the karst region of Guizhou Province, a numerical simulation model of edaphic nitrogen element transport under field conditions is initially established. In this model, NO and NH are regarded as soil solutes. Transformation mechanisms such as biological release, bio-immobilization, ammonium adsorption-desorption, nitration-denitrification and factors of crop root uptaking are considered in this model. It is hoped that the data from this model could directly be used to guide agricultural production in this region and offer feasible ways to improve the use of nitrogen element, sustainable development of agriculture in karst mountainous areas and natural environment. [ABSTRACT FROM AUTHOR]

We conducted ship-board incubation experiments to investigate changes in nutrient uptake of phytoplankton under different phosphate concentrations and irradiances in the Changjiang River Estuary and its adjacent waters in China. Under 100% natural irradiance the uptake rates of phosphate, silicate, and nitrate were accelerated at high phosphate levels (1.84 μM), while under low irradiance (about 50% natural irradiance) their uptake rates were restrained at the high but stimulated greatly at the intermediate phosphate concentrations (1.26 μM), as the growth of phytoplankton, changes in nitrite and ammonium uptake didn’t follow an obvious pattern. Our results also showed that there were linear relationships between nitrate, silicate and phosphate uptake at different phosphate concentrations under low and high irradiances, and the growth period of phytoplankton was prolonged both at the high phosphate concentrations under high irradiance and at the intermediate concentrations under low irradiance, suggesting that the limitation of phytoplankton growth mainly reflected changes in its growth period, and because no such environment (low irradiance and low phosphate concentrations) actually existed in a high turbidity zone, phytoplankton blooms hardly occurred there. In the absence of irradiance, denitrification occurred readily and phytoplankton was kept decreasing, which resulted in phosphate regeneration. [ABSTRACT FROM AUTHOR]

Low light intensity is common in northern China due to fog or haze, and causes stress for crop plants. To solve the problem of low light intensity stress on the growth and development of vegetable crops in China, new cropping strategies must be developed. We previously showed that an appropriate ratio of ammonium and nitrate (NH4+:NO3−) can alleviate the effect of low light stress on plants, although it is not clear what mechanism is involved in this alleviation. We propose the hypothesis that an appropriate ammonium/nitrate ratio (10:90) can induce NO synthesis to regulate the AsA-GSH cycle in mini Chinese cabbage seedlings under low light intensity. To test the hypothesis, we conducted a series of hydroponic experiments. The results indicated that, under low light intensity conditions, appropriate NH4+:NO3− (N, NH4+:NO3− = 10:90) decreased the contents of malondialdehyde (MDA), hydrogen peroxide (H2O2), and superoxide anion (O2−) in leaves compared with nitrate treatment. Exogenous nitric oxide (SNP) had the same effects on MDA, H2O2, and O2−. However, with the addition of a NO scavenger (hemoglobin, Hb) and NO inhibitors (N-nitro-l-arginine methyl ester, L-NAME), NaN3 (NR inhibitor) significantly increased the contents of MDA, H2O2, and O2-. The application of N solution enhanced the AsA-GSH cycle by increasing the activities of ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and ascorbate oxidase (AAO), compared with control (NH4+:NO3− = 0:100). Meanwhile, exogenous SNP significantly increased the above indicators. All these effects of N on AsA-GSH cycle were inhibited by the addition of Hb, L-NAME and NaN3 in N solution. The results also revealed that the N and SNP treatments upregulated the relative expression level of GR, MDHAR1, APXT, DHAR2, and AAO gene in mini Chinese cabbage leaves under low light stress. These results demonstrated that the appropriate NH4+:NO3− (10:90) induced NO synthesis which regulates the AsA-GSH cycle in mini Chinese cabbage seedlings under low light stress. [ABSTRACT FROM AUTHOR]