Soluble Organic Nitrogen Research Articles

Modelling transportation and transformation of nitrogen compounds at different influent concentrations in sewer pipe

A mathematical model was established to describe the transportation and transformation of nitrogen compounds in the sewer pipe. In order to verify the consistency between the experimental data and model simulation data, four runs of experiments were carried out in a 21m long, 0.15m diameter model sewer. The results showed a good consistency between the experimental and simulation values (all correlation coefficients >0.81). According to the good consistency, it was proved that the attached heterotrophic biofilm on the sewer bottom played a dominant role on degradation of compounds in the system. Readily biodegradable substrate (SS) decreased with the test time due to aerobic and anoxic growth of heterotrophs. Ammonia and ammonium nitrogen (SNH) increased with the test time. But nitrate and nitrite nitrogen (SNO) and soluble organic nitrogen (SND) decreased. Dissolved oxygen (SO) declined due to the microbial consumption and subsequently increased due to reaeration, forming a sag curve. Furthermore, the transformation pathways of different compounds were identified in this study.

Molecular characterization of water soluble organic nitrogen in marine rainwater by ultra-high resolution electrospray ionization mass spectrometry

Abstract. Atmospheric water soluble organic nitrogen (WSON) is a subset of the complex organic matter in aerosols and rainwater, which impacts cloud condensation processes and aerosol chemical and optical properties and may play a significant role in the biogeochemical cycle of N. However, its sources, composition, connections to inorganic N, and variability are largely unknown. Rainwater samples were collected on the island of Bermuda (32.27° N, 64.87° W), which experiences both anthropogenic and marine influenced air masses. Samples were analyzed by ultra-high resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry to chemically characterize the WSON. Elemental compositions of 2281 N containing compounds were determined over the mass range m/z+ 50 to 500. The five compound classes with the largest number of elemental formulas identified, in order from the highest number of formulas to the lowest, contained carbon, hydrogen, oxygen, and nitrogen (CHON+), CHON compounds that contained sulfur (CHONS+), CHON compounds that contained phosphorus (CHONP+), CHON compounds that contained both sulfur and phosphorus (CHONSP+), and compounds that contained only carbon, hydrogen, and nitrogen (CHN+). Compared to rainwater collected in the continental USA, average O:C ratios of all N containing compound classes were lower in the marine samples whereas double bond equivalent values were higher, suggesting a reduced role of secondary formation mechanisms. Despite their prevalence in continental rainwater, no organonitrates or nitrooxy-organosulfates were detected, but there was an increased presence of organic S and organic P containing compounds in the marine rainwater. Cluster analysis showed a clear chemical distinction between samples collected during the cold season (October to March) which have anthropogenic air mass origins and samples collected during the warm season (April to September) with remote marine air mass origins. This, in conjunction with patterns identified in van Krevelen diagrams, suggests that the cold season WSON is a mixture of organic matter with both marine and anthropogenic sources while in the warm season the WSON appears to be dominated by marine sources. These findings indicate that, although the concentrations and percent contribution of WSON to total N is fairly consistent across diverse geographic regions, the chemical composition of WSON varies strongly as a function of source region and atmospheric environment.

Soluble inorganic and organic nitrogen in two Australian soils under sugarcane cultivation

Addressing the limited knowledge of nitrogen (N) pools in tropical agricultural soils and the need to reduce N losses from these systems, we analysed soluble organic and inorganic N in two Hydrosols under sugarcane. Concentrations of ammonium and nitrate spanned ∼3 – orders of magnitude (0.2–41.0mg ammonium-N, 0–10.7mg nitrate-Nkg−1soil) with the highest concentrations detected within 2–3 months of fertiliser application. Soluble amino acids spanned 1-order of magnitude (0.22–2.42mg amino acid-Nkg−1soil) and accounted for up to 70% of the low-molecular weight N. Amino acid concentrations were usually highest in the wet season and uniform across soil depth, indicating that amino acids are generated throughout the studied profile. We compared soluble and dissolved (free) N in the soil solution in a subset of samples. In soil solution, amino acid, ammonium and nitrate concentrations averaged 20, 265 and 1820μM, respectively, corresponding to ∼10% (amino acids), ∼20% (ammonium) and ∼100% (nitrate) of the soluble N pool. We calculated an annual gross amino acid flux in the dissolved N pool in the order of 2–6tonsNha−1yr−1 in the upper 40cm of soil. We discuss whether amino acids can significantly contribute to the N demand of sugarcane.

Soil enzyme activities as potential indicators of soluble organic nitrogen pools in forest ecosystems of Northeast China

Soluble organic nitrogen is considered to reflect the effect of forest types on soil nitrogen status. As a major process affecting the soil-soluble organic nitrogen pool, degradation of insoluble organic nitrogen in the production of soluble organic nitrogen is mediated by a suite of soil enzymes. This study aims to examine soil-soluble organic nitrogen pools and their relationships with the activities of soil enzymes in natural secondary forest stands and adjacent larch plantation stands. Four pairs of larch plantation stands and secondary forest stands were randomly selected from a mountainous area, and the top 15 cm of the mineral soils were sampled from each field. The soil-soluble organic nitrogen concentrations were up to 2-fold greater in the secondary forest stands than in the larch plantation stands, whereas the ratio of soluble organic nitrogen/total nitrogen was comparable between the two forest types. The concentrations of soluble organic nitrogen were positively correlated with approximately 2-fold differences in urease and protease activities, a 1.2-fold difference in N-acetyl-β-glucosaminidase and a 1.7-fold difference in l-asparaginase between the two forest types. Our results suggest that relationships between soil-soluble organic nitrogen and enzyme activities are independent on sampling time, and that the soil enzyme activities can be used as potential indicators of soil soluble organic nitrogen pools in the temperate forest ecosystem.

Vertical distribution of soluble organic nitrogen, nitrogen mineralization, nitrification, and amidohydrolase activities in a manure‐treated soil

AbstractRecent studies indicate that soil soluble organic nitrogen (SON) plays an important regulatory role in the soil–plant N cycle. The aims of this study were to identify the vertical distribution of SON and its correlation with N mineralization, nitrification, and amidohydrolase activities, in a soil repeatedly amended with cow manure or chemical fertilizer. For this purpose, soil samples were collected from 0–20, 20–40, 40–60, 60–80, and 80–100 cm depths of a calcareous soil, which has been annually amended for 5 y with cow manure (CM) at two rates of 50 (CM50) and 100 (CM100) Mg CM ha–1 y–1. Treatments with chemical fertilizer (CF) and a control (CT) were also included. Soluble organic N, N mineralization, nitrification rates, as well as L‐glutaminase and L‐asparaginase activities were determined. Both CM50 and CM100 enhanced SON content throughout the soil profile. Nitrogen‐mineralization rate (Nm) was increased at the 0–20 cm depth of the CM100 treatment and remained unaffected at the deeper depths. Nitrification rate (Nn) was significantly higher at the 0–60 cm depth of CM100 compared to CF and CT. L‐glutaminase and L‐asparaginase activities were significantly increased at the 0–40 cm depth in both CM50 and CM100 compared to CF and CT. The amidohydrolase activities could not be detected below 40 cm, regardless of the fertilizer treatments. Our results suggest that SON makes a minor contribution to N mineralization in deep soil layers. It was also concluded that changes in the SON throughout the soil profile were not associated with changes in the N‐transformation rates (Nm and Nn) and amidohydrolase activities. While we conclude that SON is a major N pool in the whole profile of the manure applied soil further investigation is required to characterize SON and to investigate the bioavailability of SON for microbial activity in different soil depths.

Urea: An important piece of Water Soluble Organic Nitrogen (WSON) over the Eastern Mediterranean

The role of atmospheric urea on the biogeochemical cycle of Water Soluble Organic Nitrogen (WSON) in the Eastern Mediterranean was assessed by collecting and analyzing wet and dry deposition samples and size segregated aerosols during a one year period (2006). In rain water volume weighted mean (VWM) concentration of urea was found equal to 5.5 μM. In atmospheric particles the average concentration of urea in coarse and fine mode was 0.9 ± 1.9 nmol N m − 3 (median 0.0 nmol N m − 3 ) and 2.2 ± 3.0 nmol N m − 3 (median 1.1 nmol N m − 3 ), respectively. The percentage contribution of urea to WSON fraction was 0% and 20% in coarse and fine particles respectively. On an annual basis 0.81 mmol m − 2 and 1.78 mmol m − 2 of urea were deposited via wet and dry deposition, contributing to WSON by 10% and 11% respectively. Regression analysis of urea with the main ions and trace metals measured in parallel suggest that soil and anthropogenic activities significantly contribute to atmospheric urea. Comparison of dry deposition of urea using size segregated deposition velocities with urea collected on a glass bead collector suggested the existence of significant fraction of urea in the gas phase.

Denitrification potential in subsoils: A mechanism to reduce nitrate leaching to groundwater

Understanding subsurface denitrification potential will give greater insights into landscape nitrate (NO 3 −) delivery to groundwater and indirect nitrous oxide (N 2O) emissions to the atmosphere. Potential denitrification rates and ratios of N 2O/(N 2O + N 2) were investigated in intact soil cores collected from 0–0.10, 0.45–0.55 and 1.20–1.30 m depths representing A, B and C soil horizons, respectively from three randomly selected locations within a single intensively managed grazed grassland plot in south eastern Ireland. The soil was moderately well drained with textures ranging from loam to clay loam (gleysol) in the A to C horizon. An experiment was carried out by amending soils from each horizon with (i) 90 mg NO 3 −–N as KNO 3, (ii) 90 mg NO 3 −–N + 150 mg glucose-C, (iii) 90 mg NO 3 −–N + 150 mg DOC (dissolved organic carbon, prepared using top soil of intensively managed grassland) kg −1 dry soil. An automated laboratory incubation system was used to measure simultaneously N 2O and N 2, at 15 °C, with the moisture content raised by 3% (by weight) above the moisture content at field capacity (FC), giving a water-filled pore space (WFPS) of 80, 85 and 88% in the A, B and C horizons, respectively. There was a significant effect ( p < 0.01) of soil horizon and added carbon on cumulative N 2O emissions. N 2O emissions were higher from the A than the B and C horizons and were significantly lower from soils that received only nitrate than soils that received NO 3 − + either of the C sources. The two C sources gave similar N 2O emissions. The N 2 fluxes differed significantly ( p < 0.05) only between the A and C horizons. During a 17-day incubation, total denitrification losses of the added N decreased significantly ( p < 0.01) with soil depth and were increased by the addition of either C source. The fraction of the added N lost from each horizon were A: 25, 61, 45%; B: 12, 29, 28.5% and C: 4, 20, 18% for nitrate, nitrate + glucose-C and nitrate + DOC, respectively. The ratios of N 2O to N 2O + N 2 differed significantly ( p < 0.05) only between soil horizons, being higher in the A (0.58–0.75) than in the deeper horizons (0.10–0.36 in B and 0.06–0.24 in C), clearly indicating the potential of subsoils for a more complete reduction of N 2O to N 2. Stepwise multiple regression analysis revealed that N 2O flux increased with total organic C and total N but decreased with NO 3 −–N which together explained 88% of the variance ( p < 0.001). The N 2 flux was best explained ( R 2 = 0.45, p < 0.01) by soluble organic nitrogen (SON) (positive) and with NO 3 −–N (negative). Stepwise multiple regression revealed a best fit for total denitrification rates which were positive for total C and negative for NO 3 −–N with the determination coefficient of 0.76 ( p < 0.001). The results suggest that without C addition, potential denitrification rate below the root zone was low. Therefore, the added C sources in subsoils can satisfactorily increase nitrate depletion via denitrification where the mole fraction of N 2O would be further reduced to N 2 during diffusional transport through the soil profile to the atmosphere and/or to groundwater. Subsoil denitrification can be accelerated either through introducing C directly into permeable reactive barriers and/or indirectly, by irrigating dirty water and manipulating agricultural plant composition and diversity.

Co-digestion of intermediate landfill leachate and sewage sludge as a method of leachate utilization

This study examines the co-digestion of intermediate landfill leachate and sewage sludge from a municipal wastewater treatment plant. Application of leachate as a co-fermentation component increased the concentrations of soluble organic compounds (expressed as total organic carbon), ammonium nitrogen, and alkalinity in the digester influents. The biogas yield obtained from the co-fermentation of a 20:1 sewage sludge: intermediate leachate mixture was 1.30 m(3) per kg of removed volatile solids (VS), while that from a 10:1 mixture was 1.24 m(3) per kg of removed VS. These values exceeded the biogas yield for the sludge alone by 13% and 8%, respectively. The leachate addition influenced the proportion of methane to a minor extent. Increased methane yields of 16.9% and 6.2% per kg of removed VS were found for the two sewage sluge:intermediate leachate mixtures, respectively.

Effects of different groundcover matters on nutrient availability in an integrated apple orchard in Eastern-Hungary

The aim of our study is to examine the effects of different groundcover methods on nutrient availability and uptake of apple orchard. Theexperiment was carried out at the orchard of TEDEJ Rt. at Hajdúnánás-Tedej, in Eastern Hungary. The orchard was set up on lowland chernozem soil in the Nyírség region. It was established in the autumn of 1999, using Idared cultivar grafted on MM106 rootstocks at a spacing of 3.8 x 1.1 m.The applied treatments were divided into two groups according to origins and effects. On the one hand, different livestock manures (cow,horse and pig), on the other hand different mulch-matters (straw, pine bark mulch, black foil) were used. The different manures and mulcheswere applied on the surface to test the effectiveness of these materials.The effectiveness of manure treatments was higher than the other treatments on AL soluble P content of soil. Mostly the manure treatmentsincreased the AL soluble K of soil. Our all treatments increased 0.01 M CaCl2 soluble NO3 - -N content of the examined soil layers. The effectof manure treatments was the highest. From the results it was evident that the amount of easily soluble organic nitrogen fraction distributedmore homogeneously than the other mineral N fractions examined.Our results can be summarized as follows:1. Our results pointed out that the used ground covering matters divided into several categories regarding its effect.2. The available N, P and K contents of soil were mostly increased by applying manures.3. The effectiveness of straw, mulch and mostly black foil was lower.4. Differences were found between nutrient supplying treatments and the treatments which did not supply nutrients.

Assessing soluble organic nitrogen pools in horticultural soils: a case study in the suburbs of Shanghai (China)

Soil soluble organic nitrogen plays a significantly important role in nitrogen biogeochemical cycling. The aim of this study was to investigate the amount of soluble organic and inorganic nitrogen pools extracted by water, salt solutions, and centrifugal-drainage technique from different horticultural management system soils. Approximately 5.4–16.6, 4.4–46.5, 7.1–18.2, 8.8–27.8, 1.8–5.6, and 1.7–4.4 mg kg − 1 soluble organic nitrogen were obtained by 1M KCl, 0.5M K2SO4, 10 mM CaCl2, 1/15 mM phosphate buffer (pH 7.0), water, and centrifugal-drainage technique, respectively, in the 0–20 cm horticultural soils. Large variation in soluble organic nitrogen pools was observed across the sites in the present study and the volumes of soluble organic nitrogen pools generally followed the order: organic production system soil > conventional production system soil > transitional production system soil. In relative contrast to soluble organic nitrogen, organic management, known primarily for the absence of artificial fertilizers and pesticides, resulted in significantly lower levels of both soluble inorganic nitrogen and total soluble nitrogen in the soil. The degree of soluble inorganic nitrogen recovery appears highly dependent on the different chemical extractants and generally followed the series: phosphate buffer (pH 7.0) > KCl≈K2SO4 > CaCl2 > water > centrifugal-drainage technique. The soluble organic carbon and nitrogen in all soil extracts were all positively related to soil total carbon, total nitrogen, and electric conductivity value. This suggested that soil total carbon and nitrogen played a central role in the retention of soluble organic nitrogen in soils. Further studies on investigating the soluble organic nitrogen degradation pathway and its bottleneck are warranted.

Soluble organic nitrogen pools in greenhouse and open field horticultural soils under organic and conventional management: A case study

The aim of this study was to investigate the influence of four different horticultural management practices in open field and in greenhouse conditions under organic and conventional cultivation on the amount of soluble organic nitrogen (SON) present in the soil. Soils used in greenhouses and open field cultivation were sampled in Shanghai, China, where organic farming has been conducted for 3 years or conventional faming has been continued in the same area. The amounts of SON, nitrate (NO 3 −) and ammonium (NH 4 +) were greater in the greenhouse soils than those under open field cultivation, which indicated a higher degree of soil management was imposed under greenhouse conditions. Greenhouse cultivation is also known to accelerate the turnover of SON in the soils, which may explain the significantly higher amounts of SON present in these soils. Organic farming, which does not use artificial fertilizers and pesticides, also resulted in significantly higher amounts of SON (average 42.10 mg kg −1) compared with soils under conventional faming (24.59 mg kg −1). The reasons for the observed differences in pool sizes of soluble inorganic nitrogen (SIN) and NO 3 − in the greenhouse soils and the open fields include (a) the heavy application of both complex fertilizer and organic fertilizer that exceeded crop requirements and (b) warmer temperatures and moist soils in the greenhouses, which are likely to lead to greater rates of N cycling compared with the open field soils. These results suggest that SON may be an important source of N in all horticultural systems, representing a pool of labile N readily available for plant growth. However, its concentration is less sensitive to different management practices than SIN. In contrast to SON, the total soluble nitrogen and inorganic N (SIN) pools varied widely with the different management practices although they were dominated by NO 3 − in all treatments. Soil organic N was positively related to dissolved organic carbon and NO 3 − contents. This relationship indicates that NO 3 − and dissolved organic matter play a key role in the retention of SON in soil.

Estimation of atmospheric nutrient inputs to the Atlantic Ocean from 50°N to 50°S based on large‐scale field sampling: Fixed nitrogen and dry deposition of phosphorus

Atmospheric nitrogen inputs to the ocean are estimated to have increased by up to a factor of three as a result of increased anthropogenic emissions over the last 150 years, with further increases expected in the short‐ to mid‐term at least. Such estimates are largely based on emissions and atmospheric transport modeling, because, apart from a few island sites, there is very little observational data available for atmospheric nitrogen concentrations over the remote ocean. Here we use samples of rainwater and aerosol we obtained during 12 long‐transect cruises across the Atlantic Ocean between 50°N and 50°S as the basis for a climatological estimate of nitrogen inputs to the basin. The climatology is for the 5 years 2001–2005, during which almost all of the cruises took place, and includes dry and wet deposition of nitrate and ammonium explicitly, together with a more uncertain estimate of soluble organic nitrogen deposition. Our results indicate that nitrogen inputs into the region were ∼850–1420 Gmol (12–20 Tg) N yr−1, with ∼78–85% of this in the form of wet deposition. Inputs were greater in the Northern Hemisphere and in wet regions, and wet regions had a greater proportion of input via wet deposition. The largest uncertainty in our estimate of dry inputs is associated with variability in deposition velocities, while the largest uncertainty in our wet nitrogen input estimate is due to the limited amount and uneven geographic distribution of observational data. We also estimate a lower limit of dry deposition of phosphate to be ∼0.19 Gmol P yr−1, using data from the same cruises. We compare our results to several recent estimates of N and P deposition to the Atlantic and discuss the likely sources of uncertainty, such as the potential seasonal bias introduced by our sampling, on our climatology.

Effluent Organic Nitrogen (EON): Bioavailability and Photochemical and Salinity-Mediated Release

The goal of this study was to investigate three potential ways that the soluble organic nitrogen (N) fraction of wastewater treatment plant (WWTP) effluents, termed effluent organic N (EON), could contribute to coastal eutrophication--direct biological removal, photochemical release of labile compounds, and salinity-mediated release of ammonium (NH4+). Effluents from two WWTPs were used in the experiments. For the bioassays, EON was added to water from four salinities (approximately 0 to 30) collected from the James River (VA) in August 2008, and then concentrations of N and phosphorus compounds were measured periodically over 48 h. Bioassay results, based on changes in DON concentrations, indicate that some fraction of the EON was removed and that the degree of EON removal varied between effluents and with salinity. Further, we caution that bioassay results should be interpreted within a broad context of detailed information on chemical characterization. EON from both WWTPs was also photoreactive, with labile NH4+ and dissolved primary amines released during exposure to sunlight. We also present the first data that demonstrate that when EON is exposed to higher salinities, increasing amounts of NH4+ are released, further facilitating EON use as effluent transits from freshwater through estuaries to the coast.

Genotype and slope position control on the availability of soil soluble organic nitrogen in tea plantations

Soluble organic nitrogen (SON) plays a vital role in ecosystem N cycling processes and is controlled by a number of biotic and abiotic factors. We compared soil SON availability, microbial biomass, protease and asparaginase activities and phospholipids fatty acid (PLFA) profiles at the 0–15 and 15–30 cm layers in 10 year old tea plantations of two genotypes—Oolong tea (Camellia sinensis (L.) O. Kuntze cv. Huangjingui) (designated as ‘OT’) and Green tea (C. sinensis (L.) O. Kuntze cv. Fuyun 6) (designated as ‘GT’)—established at different slope positions. Concentrations of soil SON measured by the 2 M KCl extraction under the OT plantation were greater than under the GT plantation, while concentrations of soil SON were greater in the middle slope (MS) and lower slope (LS) positions than in the upper slope (US) position. Trends in soil microbial biomass C and N and protease and asparaginase activities between the two genotypes and across the slope positions were similar to the SON pools. The fungal-to-bacterial ratios were higher in the US position than in the MS and LS positions and higher under the GT plantation than under the OT plantation. Results from this study support that the genotype and the slope position are key factors controlling the availability of soil SON in tea plantations and also imply the importance of plant traits (e.g. litter quantity and chemistry) and soil texture in determining overall soil N availability and transformation processes and microbial community composition at the landscape level.

Soil soluble organic carbon and nitrogen pools under mono- and mixed species forest ecosystems in subtropical China

Purpose The objective of the present study was to assess the differences in soil total C and N, microbial biomass C and N, soil soluble organic C and N among eight mono- and mixed species forest ecosystems (18-year-old restoration) in subtropical China.

Aerosol organic nitrogen over the remote Atlantic Ocean

Water soluble organic nitrogen (WSON) has been measured in aerosols collected on three research cruises on the Atlantic Ocean from approximately 55°N to 45°S. Results are interpreted using air mass back trajectories and results for other aerosol components. WSON concentrations range from 1 μm) aerosol. Concentrations of WSON were highest in samples containing Saharan dust, suggesting a locally significant source associated with soil dust. More generally WSON concentrations were highest in air which had recently crossed continental areas. In the whole data set, WSON is well correlated to total soluble nitrogen and represents approximately 25% of total nitrogen. This correlation implies a significant anthropogenic contribution to the organic nitrogen.

Nitrogen removal during summer and winter in a primary facultative waste stabilization pond: preliminary findings from 15N-labelled ammonium tracking techniques

Nitrogen removal mechanisms and pathways within WSP have been the focus of much research over the last 30 years. Debates and theories postulated continue to refine our knowledge regarding the cycling and removal pathways for this important nutrient, but a succinct answer has yet to be provided for holistic nitrogen removal. In this study, two experimental runs using labelled (15)N as a stable isotope tracking technique were conducted on a pilot-scale primary facultative WSP in the UK; one in the summer of 2006, and the other in the winter of 2007. An ammonium chloride ((15)NH(4)Cl) spike was prepared as the slug for each experimental run, which also contained rhodamine WT to act as a dye tracer enabling the hydraulic characteristics of the pond to be mapped. Initial results from the study are reported here, and findings are compared and contrasted. Preliminary findings reveal that a greater proportion of (15)N is incorporated into the algal biomass by assimilation and subsequent release as soluble organic nitrogen in summer than in winter. (15)N ammonium passes out of the system much sooner and in a much higher proportion in the winter than in summer.

Occurrence of water soluble organic nitrogen in aerosols at a coastal area

Aerosol samples (205) were collected from January 2005 to November 2006 at a coastal site at Keelung City (Taiwan), on the southern East China Sea. The atmospheric concentrations of major ions indicated that the area was dominated by different air masses at different times of the year: continental Asia from January to May and November to December; air masses from Indonesia and surrounding islands (south-eastern region) dominated during early-summer (July 2005 and June 2006), and air masses directly from the adjacent ocean dominated during late-summer (July to August 2006) and early-autumn (September to October 2005). The atmospheric concentrations of water soluble organic nitrogen (WSON) corresponded to the different sources and weather conditions. The results of a factor analysis of combined major ions, water soluble inorganic nitrogen (WSIN) and WSON indicated that a fossil fuel combustion source and biomass burning were the two major controlling factors during the sampling period. We discuss the correlations between WSON, WSIN and major anthropogenic ions in relation to the different formation mechanisms for the various sources. We propose a mechanism whereby biomass burning is the major input of aerosols derived from mainland China. Fossil fuel combustion was found to be important during periods when aerosols were derived from the south-eastern area. Our data indicate that WSON was predominantly associated with aerosols derived from biomass burning when the origin of the air mass was mainland China.

Soil soluble organic nitrogen and active microbial characteristics under adjacent coniferous and broadleaf plantation forests

Soil soluble organic nitrogen (SON) is considered as a sensitive indicator of soil nitrogen (N) status and plays an important role in N cycling in forest ecosystems. Most work on forest soil SON to date has been conducted in temperate areas. The information about soil SON pools and dynamics in tropical and subtropical areas is limited. The aim of this study was to investigate the effects of different forest types on soil SON availability and associated microbial properties. Soil samples were collected at two depths (0–20 and 20–40 cm) from adjacent 12-year-old plantation forests of coniferous Chinese fir (Cunninghamia lanceolata (Lamb) Hook; Coniferous Fir), coniferous–broadleaf mixed species of broadleaf Nagai Podocarpus and coniferous Pond cypress (mixed species), and broadleaf Phoebe nanmu (broadleaf Phoebe) in subtropical China. Three extraction methods (water, hot water, and 2 M KCl) were used for measurements of SON. Soil microbial biomass carbon (C) and N and activities of urease, protease, and l-asparaginase were also measured. Hot water and KCl extractable SON pools were greater in the surface soils (0–20 cm) under the broadleaf Phoebe than under the Coniferous Fir, while those under the mixed species were intermediate. The microbial biomass C and N as well as activities of protease and urease were higher in the soils under the broadleaf Phoebe and mixed species than under the Coniferous Fir. Soluble organic C and SON pools were positively related to soil total C and N and microbial biomass C and microbial biomass N. Activities of urease, protease, and asparaginase were highly correlated with SONw, SONhw, and SONKCl. This work has demonstrated that forest type had significant impacts on the pool size of soil SON. This may be attributed to the different quantity and quality of organic inputs from different forest systems. Positive relationships between microbial biomass and enzyme activities with the SON pools clearly demonstrated that microbial communities play a vital role in the dynamics of soil SON in forest ecosystems. It is recommended that soil SON measured by hot water extraction be incorporated into the routine measurement of soil available N in forest ecosystems. Further study on the role of specific microbial functional groups in the SON transformation and the chemical nature and seasonal dynamics of SON pools in forest ecosystems is warranted.

Atmospheric nitrogen deposition in south-east Scotland: Quantification of the organic nitrogen fraction in wet, dry and bulk deposition

Water soluble organic nitrogen (WSON) compounds are ubiquitous in precipitation and in the planetary boundary layer, and therefore are a potential source of bioavailable reactive nitrogen. This paper examines weekly rain data over a period of 22 months from June 2005 to March 2007 collected in 2 types of rain collector (bulk deposition and “dry + wet” deposition) located in a semi-rural area 15 km southwest of Edinburgh, UK (N55°51′44″, W3°12′19″). Bulk deposition collectors are denoted in this paper as “standard rain gauges”, and they are the design used in the UK national network for monitoring precipitation composition. “Dry + wet” deposition collectors are flushing rain gauges and they are equipped with a rain detector (conductivity array), a spray nozzle, a 2-way valve and two independent bottles to collect funnel washings (dry deposition) and true wet deposition. On average, for the 27 weekly samples with 3 valid replicates for the 2 types of collectors, dissolved organic nitrogen (DON) represented 23% of the total dissolved nitrogen (TDN) in bulk deposition. Dry deposition of particles and gas on the funnel surface, rather than rain, contributed over half of all N-containing species (inorganic and organic). Some discrepancies were found between bulk rain gauges and flushing rain gauges, for deposition of both TDN and DON, suggesting biological conversion and loss of inorganic N in the flushing samplers.