Seasonal differences in sources and formation processes of PM2.5 nitrate in an urban environment of North China.

Nitrate (NO3-) has been the dominant ion of secondary inorganic aerosols (SIAs) in PM2.5 in North China. Tracking the formation mechanisms and sources of particulate nitrate are vital to mitigate air pollution. In this study, PM2.5 samples in winter (January 2020) and in summer (June 2020) were collected in Jiaozuo, China, and water-soluble ions and (δ15N, δ18O)-NO3- were analyzed. The results showed that the increase of NO3- concentrations was the most remarkable with increasing PM2.5 pollution level. δ18O-NO3- values for winter samples (82.7‰ to 103.9‰) were close to calculated δ18O-HNO3 (103‰ ± 0.8‰) values by N2O5 pathway, while δ18O-NO3- values (67.8‰ to 85.7‰) for summer samples were close to calculated δ18O-HNO3 values (61‰ ± 0.8‰) by OH oxidation pathway, suggesting that PM2.5 nitrate is largely from N2O5 pathway in winter, while is largely from OH pathway in summer. Averaged fractional contributions of PN2O5+H2O were 70% and 39% in winter and summer sampling periods, respectively, those of POH were 30% and 61%, respectively. Higher δ15N-NO3- values for winter samples (3.0‰ to 14.4‰) than those for summer samples (-3.7‰ to 8.6‰) might be due to more contributions from coal combustion in winter. Coal combustion (31% ± 9%, 25% ± 9% in winter and summer, respectively) and biomass burning (30% ± 12%, 36% ± 12% in winter and summer, respectively) were the main sources using Bayesian mixing model. These results provided clear evidence of particulate nitrate formation and sources under different PM2.5 levels, and aided in reducing atmospheric nitrate in urban environments.

Initiation of efficient C4 pathway in response to low ambient CO2 during the bloom period of a marine dinoflagellate.

Dinoflagellates are important primary producers and major causative agents of harmful algal blooms in the global ocean. Despite the great ecological significance, the photosynthetic carbon acquisition by dinoflagellates is still poorly understood. The pathways of photosynthetic carbon assimilation in a marine dinoflagellate Prorocentrum donghaiense under both in situ and laboratory-simulated bloom conditions were investigated using a combination of metaproteomics, qPCR, stable carbon isotope and targeted metabolomics approaches. A rapid consumption of dissolved CO2 to generate high biomass was observed as the bloom proceeded. The carbon assimilation genes and proteins including intracellular carbonic anhydrase 2, phosphoenolpyruvate carboxylase, phosphoenolpyruvate carboxykinase and RubisCO as well as their enzyme activities were all highly expressed at the low CO2 level, indicating that C4 photosynthetic pathway functioned in the blooming P. donghaiense cells. Furthermore, δ13 C values and content of C4 compound (malate) significantly increased with the decreasing CO2 concentration. The transition from C3 to C4 pathway minimizes the internal CO2 leakage and guarantees efficient carbon fixation at the low CO2 level. This study demonstrates the existence of C4 photosynthetic pathway in a marine dinoflagellate and reveals its important complementary role to assist carbon assimilation for cell proliferation during the bloom period.

Novel Position-Specific 18O/16O Measurement of Carbohydrates. II. The Complete Intramolecular 18O/16O Profile of the Glucose Unit in a Starch of C4 Origin.

Information about plant photosynthetic carbon assimilation, physiology, and biochemistry is locked in the 18O/16O ratios of the individual positions of higher plants carbohydrates but is under-utilized, because of the difficulty of making these determinations. We report the extension of the wet chemistry approach we used to access the 18O/16O ratio of O-3 of glucose with a novel GC/Pyrolysis/IRMS-based method, to determine the 18O/16O ratios of O-4, O-5, and O-6. The O atoms (OH groups) at positions 1, 2, 5, and 6 of glucose were protected by acetonation (converting to 1,2;5,6-di-O-isopropylidene-glucofuranose, DAGF). The DAGF was then converted to 6-bromo-6-deoxy-1,2;3,5-di-O-isopropylidene-glucofuranose (6-bromoDAGF) with the simultaneous removal of O-6 with N-bromosuccinimide and triphenylphosphine. The DAGF was also methylated at O-3 with CH3I under the catalysis of NaH to 3-methylDAGF, which was then deacetonated to 1,2-O-isopropylidene-3-O-methyl-glucofuranose (3-methylMAGF). O-5 and O-6 were then removed as a whole from 3-methylMAGF by I2 oxidization under the catalysis of Ph3P and imidazole. Isotope mass balance was then applied to calculate the 18O/16O of O-5 and O-6 as a whole and O-6, respectively. Sampling at different stages of substrate conversion to product and applying a Rayleigh-type fractionation model were employed, when quantitative conversion of substrate was unachievable to calculate the δ18O of the converted substrate. Quantitative conversion of glucose with phenylhydrazine to phenylglucosazone also allowed for the calculation of δ18O2 by applying isotope mass balance between the two. A C4 starch-derived glucose intramolecular δ18O profile is now determined: O-3 is relatively enriched (by 12.16 mUr), O-4 is relatively depleted (by 20.40-31.11 mUr), and O-2 is marginally enriched (by 2.40 mUr) against the molecular average.

Novel GC/Py/GC/IRMS-Based Method for Isotope Measurements of Nitrate and Nitrite. I: Converting Nitrate to Benzyl Nitrate for δ18O Analysis.

The 18O/16O (and 15N/14N) ratio of natural nitrate (NO3-) and nitrite (NO2-) can be used to extract valuable information about their source and fate as environmental contaminants, their metabolism as macronutrients in plants and animals, and their behavior in the N biogeochemical cycle. We developed an accurate, precise, sensitive (minimum sample size: 0.2 µg NO3--equivalent), and reliable (minimal oxygen exchange, loss, or gain) method to selectively isolate and purify nitrate and nitrite from natural water, soil, air, and plant materials by strong anion exchange (SAX) for low- to normal-salinity samples or strong cation exchange (SCX) for high-salinity samples, followed by quantitative conversion to their respective benzyl esters, which can be separated and individually analyzed for δ18O (and potentially δ15N) by gas chromatography (GC)/pyrolysis/GC/isotope-ratio mass spectrometry (IRMS). The method compares favorably with the currently popular bacterial denitrification and chemical reduction methods, in terms of sensitivity and reliability, and has the potential to simultaneously measure δ15N and δ18O of nitrate and nitrite from natural samples of various origins.

Leaf transition from heterotrophy to autotrophy is recorded in the intraleaf C, H and O isotope patterns of leaf organic matter.

RATIONALE: Quantitatively relating 13 C/12 C, 2 H/1 H and 18 O/16 O ratios of plant α-cellulose and 2 H/1 H of n-alkanes to environmental conditions and metabolic status should ideally be based on the leaf, the plant organ most sensitive to environmental change. The fact that leaf organic matter is composed of isotopically different heterotrophic and autotrophic components means that it is imperative that one be able to disentangle the relative heterotrophic and autotrophic contributions to leaf organic matter. METHODS: We tackled this issue by two-dimensional sampling of leaf water and α-cellulose, and specific n-alkanes from greenhouse-grown immature and mature and field-grown mature banana leaves, taking advantage of their large areas and thick waxy layers. Leaf water, α-cellulose and n-alkane isotope ratios were then characterized using elemental analysis isotope ratio mass spectrometry (IRMS) or gas chromatography IRMS. A three-member (heterotrophy, autotrophy and photoheterotrophy) conceptual linear mixing model was then proposed for disentangling the relative contributions of the three trophic modes. RESULTS: We discovered distinct spatial leaf water, α-cellulose and n-alkane isotope ratio patterns that varied with leaf developmental stages. We inferred from the conceptual model that, averaged over the leaf blade, only 20% of α-cellulose in banana leaf is autotrophically laid down in both greenhouse-grown and field-grown banana leaves, while approximately 60% and 100% of n-alkanes are produced autotrophically in greenhouse-grown and field-grown banana leaves, respectively. There exist distinct lateral (edge to midrib) gradients in autotrophic contributions of α-cellulose and n-alkanes. CONCLUSIONS: Efforts to establish quantitative isotope-environment relationships should take into account the fact that the evaporative leaf water 18 O and 2 H enrichment signal recorded in autotrophically laid down α-cellulose is significantly diluted by the heterotrophically formed α-cellulose. The δ2 H value of field-grown mature banana leaf n-alkanes is much more sensitive than α-cellulose as a recorder of the growth environment. Quantitative isotope-environment relationship based on greenhouse-grown n-alkane δ2 H values may not be reliable.

The effect of processing medium on the 2 H/1 H of carbon-bound hydrogen in α-cellulose extracted from higher plants.

RATIONALE: Although the 2 H/1 H ratio of the carbon-bound hydrogens (C-Hs) in α-cellulose extracted from higher plants has long been used successfully for climate, environmental and metabolic studies, the assumption that bleaching with acidified NaClO2 to remove lignin before pure α-cellulose can be obtained does not alter the 2 H/1 H ratio of α-cellulose C-Hs has nonetheless not been tested. METHODS: For reliable application of the 2 H/1 H ratio of α-cellulose C-H, we processed plant materials representing different phytochemistries and photosynthetic carbon assimilation modes in isotopically contrasting bleaching media (with an isotopic difference of 273 mUr). All the isotope ratios were measured by elemental analyzer/isotope ratio mass spectrometry (EA/IRMS). RESULTS: Our results show that H from the bleaching medium does appear in the final pure α-cellulose product, although the isotopic alteration to the C-H in α-cellulose due to the incorporation of processing H from the medium is small if isotopically "natural" water is used to prepare the processing medium. However, under prolonged bleaching such an isotope effect can be significant, implying that standardizing the bleaching process is necessary for reliable 2 H/1 H measurement. CONCLUSIONS: The currently adopted method for removing lignin for α-cellulose extraction from higher plant materials with acidified NaClO2 bleaching is considered acceptable in terms of preserving the isotopic fidelity if isotopically "natural" water is used to prepare the bleaching solution.

Novel Position-Specific 18O/16O Measurement of Carbohydrates. I. O-3 of Glucose and Confirmation of 18O/16O Heterogeneity at Natural Abundance Levels in Glucose from Starch in a C4 Plant.

The 18O/16O ratio at both molecular and positional levels in the carbohydrates of higher plants is a reliable proxy for the plant growth environment, and a potential indicator of the plant photosynthetic carbon assimilation mode, and its physiological, biochemical and metabolic status. The lack of exploitable nuclear resonance in 18O and 16O and the extremely low 17O abundance make the NMR-based PSIA (position-specific isotopic analysis) a significant challenge. In this Article, an alternative three-step wet chemistry based method for accessing the 18O/16O of glucose O-3 is presented. The O atoms (OH groups) at positions 1, 2, 5, and 6 were first protected by acetonation (converting glucose to 1,2;5,6-di- O-isopropylidene-glucofuranose). The protected glucose was then esterified at O-3 by thionoformylation. Subsequent Barton-McCombie deoxygenation quantitatively removed the O-3 from the protected sugar. Mass balance was then applied to calculate the 18O/16O of O-3 using the isotopic values of the protected sugar before and after the deoxygenation step. The method is innovative in that (i) isolation and purification of individual compounds for 18O by EA/Pyrolysis/IRMS analysis is unnecessary as the reaction mixture can be analyzed on a GC/Pyrolysis/IRMS; (ii) sample quantity is dramatically reduced; and (iii) the approach to access the O-3 isotopic signal can be easily expanded to other positions within glucose and other sugars. It was shown that O-3 is enriched by 12 mUr relative to the molecular average (O-2-O-6) for a glucose of C4 photosynthetic origin. We highlighted the potential applications of the intramolecular O isotopic heterogeneity of glucose this method revealed.

Virgibacillus oceani sp. nov. isolated from ocean sediment.

A Gram-stain-positive, moderately halophilic, motile, strictly aerobic, endospore-forming, rod-shaped bacterium, strain MY11(T), was isolated from a sediment sample collected from the Western Pacific. This isolate grew in the presence of 0.5-18% (w/v) NaCl and at pH 6.0-10.0 and 15-45 °C; optimum growth was observed with 3.5% (w/v) NaCl and at pH 8.0-9.0 and 35-37 °C. Strain MY11(T) had menaquinone 7 (MK-7) as the predominant respiratory quinone and anteiso-C15:0 and anteiso-C17:0 as major fatty acids. Major polar lipids were diphosphatidylglycerol and phosphatidylglycerol. The DNA G+C content was 34.2 mol%. Phylogenetic analysis based on 16S rRNA gene sequences confirmed that strain MY11(T) was a member of the genus Virgibacillus, exhibiting sequence similarities of 95.3-97.6% to the type strains of recognized Virgibacillus species. Strain MY11(T) could be differentiated from recognized species of the genus Virgibacillus based on phenotypic characteristics, chemotaxonomic differences, phylogenetic analysis and DNA-DNA hybridization data. On the basis of the data presented, strain MY11(T) is considered to represent a novel species of the genus Virgibacillus, for which the name Virgibacillus oceani sp. nov. is proposed. The type strain is MY11(T) ( =LMG 28105(T) =CGMCC 1.12754(T) =MCCC 1A09973(T)).

Nesterenkonia alkaliphila sp. nov., an alkaliphilic, halotolerant actinobacteria isolated from the western Pacific Ocean.

A Gram-staining-positive, aerobic, motile and non-spore-forming actinobacteria, designated strain F10(T), was isolated from a deep-sea sediment of the western Pacific Ocean. Phylogenetic and phenotypic properties of the organism supported that it belonged to the genus Nesterenkonia. Strain F10(T) shared highest 16S rRNA gene sequence similarity of 96.8 % with Nesterenkonia aethiopica DSM 17733(T), followed by Nesterenkonia xinjiangensis YIM 70097(T) (96.7 %) and Nesterenkonia alba CAAS 252(T) (96.6 %). The organism grew at 4-50 °C, at pH 7.0-12.0 and in the presence of 0-12 % (w/v) NaCl, with optimal growth occurring at 40 °C, at pH 9.0 and in the presence of 1 % (w/v) NaCl. The peptidoglycan type was A4(alpha), l-Lys-Gly-l-Glu. The polar lipid profile of strain F10(T) consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol, two unknown glycolipids and two unknown lipids. The isolate contained MK-9 (92 %) and MK-8 (5.8 %) as the major components of the menaquinone system, and anteiso-C17 : 0 (50.9 %) and anteiso-C15 : 0 (29.8 %) as the predominant fatty acids. The G+C content of the genomic DNA of strain F10(T) was 66.2 mol%. Based on phenotypic, genotypic and phylogenetic analyses, strain F10(T) represents a novel species of the genus Nesterenkonia for which the name Nesterenkonia alkaliphila sp. nov. is proposed. The type strain is F10(T) ( = LMG 28112(T) = CGMCC 1.12781(T) = JCM 19766(T) = MCCC 1A09946(T)).

Paracoccus pacificus sp. nov., isolated from the Western Pacific Ocean.

A Gram-stain negative, short rod-shaped, non-motile, catalase- and oxidase-positive, aerobic bacterium, designated F14(T), was isolated from the Western Pacific Ocean. Phylogenetic and phenotypic properties of the organism supported that it belongs to the genus Paracoccus. The levels of 16S rRNA gene sequences similarity between strain F14(T) and other type strains of recognized members of the genus Paracoccus were 93.6-96.5%. Growth of strain F14(T) was observed at 4-40 °C (optimum, 28-30 °C), pH 6.0-10.0 (optimum, pH 7.0-8.0) and in the presence of 0-7% (w/v) NaCl (optimum, 1-2%). The major cellular fatty acid was summed feature 8 (C(18:1)ω6c and/or C(18:1)ω7c). The major respiratory quinone was ubiquinone-10. The polar lipid pattern indicated the presence of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine and three unknown lipids. The DNA G+C content was 61.4 mol%. On the basis of polyphasic characterization, strain F14(T) represents a novel species, for which the name Paracoccus pacificus sp. nov. is proposed. The type strain is F14(T) (=CGMCC 1.12755(T)=LMG 28106(T)=MCCC 1A09947(T)).

Stratified communities of active archaea in shallow sediments of the Pearl River Estuary, Southern China.

Marine subsurface sediments represent a novel archaeal biosphere with unknown physiology. To get to know the composition and ecological roles of the archaeal communities within the sediments of the Pearl River Estuary, Southern China, the diversity and vertical distribution of active archaea in a sediment core were characterized by 16S rRNA phylogenetic analysis of clone libraries derived from RNA. In this study, the archaeal diversity above, within, and beneath the sulfate-methane transition zone (SMTZ) in the Pearl River Estuary sediment core was described. The majority of the clones obtained from the metabolically active fraction of the archaeal community were most closely related to miscellaneous crenarchaeotal group and terrestrial miscellaneous euryarchaeotal group. Notably, although the Pearl River Estuary sediment belong to high methane and high organic carbon environment, sequences affiliated with methanotrophic and methanogenic archaea were detected as minor group in 16S rRNA clone libraries. No obvious evidence suggested that these unknown archaeal phylotypes related directly to anaerobic oxidation of methane in SMTZ. This is the first phylogenetic analysis of the metabolically active fraction of the archaeal community in the coastal sediment environments.

Stratified communities of methanogens in the jiulong river estuarine sediments, southern china.

Methane is a potent greenhouse gas and produced mainly by methanogens. Few studies have specifically dealt so far with methanogens in estuarine environments. In this study, diversity and distribution of methanogens were investigated by clone library and T-RFLP analysis in a Jiulong River estuarine sediment core which contained clear sulfate-methane-transition zone. The majority of obtained sequences in clone libraries and T-RF peaks from T-RFLP analysis were assigned mainly to Methanosaeta, Methanomicrobiales and Methanosarcinales/ANME. The fragments of Methanosarcinales/ANME were most dominant group (mean 51 %) and composed largely of ANME-2a. In addition, Methanosaeta and Methanomicrobiales accounted for 21 and 28 % of all fragments. Therefore, the presence of Methanomicrobiales, Methanosaeta and ANME-2a was indicative of acetoclastic methanogenesis, hydrogenotrophic methanogenesis, and anaerobic methane oxidation in Jiulong River estuarine sediments. This study provided the important knowledge towards understanding methane cycling association of representative of methanogens involved in estuarine environments.

Nitrate sources and transformations along a mountain-to-plain gradient in the Taizi River basin in Northeast China.

Fifty-seven riverine samples in three typical regions, namely, upper mountainous (zone 1), middle hilly (zone 2), and lower plain (zone 3) regions, were collected in May (low flow) and August (high flow) of 2016, and chemical parameters and isotopes were analyzed to enrich the knowledge of riverine nitrate sources and transformations in the Taizi River basin. Results showed that NO3- concentrations in zone 3 were the highest, followed by zones 2 and 1. NO3-/Cl- molar ratios and nitrate dual isotopes indicated that NO3- was mainly from chemical fertilizer (CF) in zones 1 (57.0%) and 2 (43.1%) according to a Bayesian mixing model (SIAR) and mixed sources of CF, nitrification of soil organic nitrogen (SON), and manure and sewage (M&S) in zone 3 (92.8%), during the high-flow season. NO3- was mainly from CF and SON in zones 1 (76.7%) and 2 (74.0%), during the low-flow season. NO3-sources were different in the three rivers of zone 3 mainly due to various urban inputs. Contributions of CF, SON, and M&S increased by 13%, 8.3%, and 7.5% in zones 1, 2, and 3, respectively, from the low-flow to the high-flow season. NO3- in the Taizi River was mainly influenced by nitrification in soils, while no significant denitrification was found in the three zones. Measures for reducing NO3- inputs to rivers should be considered by improving effectively utilizing rate of chemical fertilizer and inhibit nitrification.

Typhoon Fung-wong (2008) induced heavy metals secondary pollution in Quanzhou Bay, southeast of China.

The concentrations of Cr, Ni, Cu, Zn, As, Cd, Pb, and Al in suspended particles were measured, and temperature, salinity, flow velocity and direction during a tidal cycle were observed before and after Typhoon Fung-wong at six stations in Quanzhou Bay, respectively. The comparison results show that, after the typhoon, the salinity in Quanzhou Bay decreased, whereas the concentrations of heavy metals increased by a factor of between 2 and 10, and the high heavy metal concentration corresponded to the low value of ratio between heavy metals and Al (HMs/Al), suggesting that these increased heavy metals were mainly from natural sources. Instantaneous unit width flux calculations for heavy metals at different stations indicate that sediments are an important source of heavy metals in suspended particles under the influence of typhoon, which has significantly contribution to understanding the impact of typhoons on the heavy metal pollution in the coastal area.

Accessing the position-specific 18O/16O ratios of lignin monomeric units from higher plants with highly selective hydrogenolysis followed by GC/Py/IRMS analysis.

The 18O/16O of lignin at bulk, molecular and positional levels can be used to extract valuable information about climate, plant growth environment, plant physiology, and plant metabolism. Access to the individual oxygen isotope compositions (δ18O) in the lignin monomeric units is, however, challenging as depolymerization of lignin to release the monomeric units may cause isotope fractionation. We have developed a novel method to measure the δ18O of the three oxygens (O-3, O-4 and O-5) attached to the aromatic ring of the monomeric units (bearing no oxygen in their side chains) releasable by highly selective W2C/AC (tungsten carbide supported by activated carbon)-catalyzed hydrogenolysis of lignin. O-4 is obtained by measuring the δ18O of H-type monomeric unit, while O-3 and O-5 can be calculated following isotope mass balance between H, G and S-type monomeric units measurable simultaneously with GC/Py/IRMS (gas chromatography-pyrolysis-isotope ratio mass spectrometry). The measurement precisions are better than 1.15 mUr and 4.15 mUr at molecular and positional levels, respectively. It was shown that there were a δ18OH > Î´18OG > Î´18OS isotopic order in the herbaceous plant lignin and an (inclusive) opposite order in woody plant lignin. Such differences in isotopic order is likely to be caused by the fact that both L-tyrosine, which carries an 18O-enriched leaf water signal, and L-phenylalanine, which carries mainly a molecular O2 isotopic signal, serve as the precursors for lignin biosynthesis in herbaceous plants while only the latter serves as precursor for lignin biosynthesis in woody plants. We have highlighted the potential application of such molecular and positional levels isotopic signals in plant physiological, metabolic, lignin biosynthetic and climate studies.

Evolution of sedimentary organic matter in a small river estuary after the typhoon process: A case study of Quanzhou Bay.

Extreme weather events occur frequently under global warming scenarios and have an important impact on the global carbon cycle. Compared to large rivers, small rivers are more sensitive to extreme weather events (such as typhoons). This paper reports the results of a study carried out in the Quanzhou Bay to explore the evolution of small river estuarine sedimentary organic matter after typhoon process using measurements of the grain-size, total organic carbon (TOC), total nitrogen (TN) and δ13C of surface sediment samples collected 2-3 days and a month, respectively, after typhoon Matmo landing in 2014. The results show that the contents of TOC and TN in the sediments, which gradually decrease from the estuary to the outer sea of Quanzhou Bay, decreased approximately 13% and 16%, respectively, a month later compared with 2-3 days after typhoon landing. The significant decrease occurred in the Jinjiang River estuary and along the South Channel of Quanzhou Bay, while the North Channel and Luoyangjiang River estuary retained high levels of TOC and TN. The results of δ13C values and TOC/TN ratios show that the organic matter in the sediment of the Quanzhou Bay was a mixture derived from C3 terrestrial plants and marine algae. The terrestrial organic matter was mainly deposited in the Jinjiang River estuary 2-3 days after typhoon landing and then spread along the tidal channel to the outer sea a month later. It indicates that the hydrodynamic forces stirred sedimentary organic matters that were input and settled during typhoon, and transported later along the North and South Channel to the outer sea. Some of those organic matters were accumulated in the North Channel during the transport process. The results provide significant meaning for the carbon cycle and material flux study on the coastal and margin seas.

Nonlinear effects of increasing nitrogen deposition on rice growth and heavy metal uptake in a red soil ecosystem of southeastern China.

With the population growth, urbanization and industrialization, China has become a hotspot of atmospheric deposition nitrogen (ADN), which is a threat to ecosystem and food safety. However, the impacts of increased ADN on rice growth and grain metal content are little studied. Based on previous long-term ADN studies, greenhouse experiment was conducted with four simulated ADN rates of 0, 30, 60 and 90 kg N ha-1 yr-1 (CK, N1, N2 and N3 as δ15N, respectively) to assess rice growth and metal uptake in a red soil ecosystem of southeast China during 2016-2017. Results showed that simulated ADN could promote rice growth and increase yields by 15.68-24.41% (except N2) and accumulations of cadmium (Cd) or copper (Cu) in organs. However, there was no linear relationship between ADN rate and rice growth or Cd or Cu uptake. The 15N-ADN was mainly accumulated in roots (21.31-67.86%) and grains (25.26-49.35%), while Cd and Cu were primarily accumulated in roots (78.86-93.44% and 90.00-96.24%, respectively). 15N-ADN and Cd accumulations in roots were significantly different between the two growing seasons (p < 0.05), implying the accumulative effects of ADN. Data also indicated the synergetic effect between accumulations of 15N-ADN and soil Cd and Cu. This study demonstrated that increasing ADN could potentially enhance Cd or Cu uptake in rice grain and threaten rice grain safety. However, related nonlinear mechanism is still needed to be discussed between increasing ADN and rice response in the future.

Improvements in the preparation of phosphate for oxygen isotope analysis from soils and sediments.

In contrast to the successful preparation of phosphate for oxygen isotope analysis from water samples, there are still a series of problems for similar analyses from soils and sediments. Here, we improved and optimized the methods of silver phosphate preparation for oxygen isotope analysis from soils and sediments. During our preparations, organic matter was removed by sodium hypochlorite and XAD-2 resin, while the impurities of elemental silver and its oxide were removed by rapid microprecipitation and ammonium phospho-molybdate and magnesium ammonium phosphate. The total organic carbon and total nitrogen in the prepared silver phosphates from soils and sediments were 0.226±0.033% and 0.030±0.0059% (n = 7), 0.217±0.053% and 0.034±0.0120% (n = 9), respectively, indicating a high removal efficiency of organic matter. We confirmed that adding citric acid during rapid microprecipitation would introduce the impurity of elemental silver, which could be removed by ammonia recrystallization. The pH range of solutions for rapid microprecipitation was optimized at 7.0‒7.5. Results of X-ray Diffraction and stable oxygen isotope analyses showed that the improved method could obtain high pure silver phosphate from soil and sediment samples without oxygen isotope fractionation. This improved procedure provides a foundation for biogeochemical studies on phosphorus in soil and lacustrine environments by using phosphate oxygen isotopes.

[Identification of Nitrate Sources and the Fate of Nitrate in Downstream Areas: A Case Study in the Taizi River Basin].

A total of 14 samples were collected in May 2016(dry season)and August 2016 (wet season) in the downstream area of the Taizi River. △15 N-NO3- and △18 O-NO3- were determined using the azide method, and △18 O-H2O was determined using a CO2-H2O equilibration technique. To identify NO3- sources and transformations in the downstream area of Taizi River Basin, ion chromatography, Nessler's reagent spectrophotometry, the azide method, and CO2-H2O equilibration methods were utilized to determine the concentrations of NO3-, Cl-, NH4+-N, and isotopic compositions (△15 N and △18 O) of NO3- and the △18 O-H2O in surface water. The results showed that the NO3- was mainly derived from mixed sources. During the dry season, the nitrate in the surface water was derived from soil nitrogen, manure, and sewage in the upper reaches, and mainly derived from synthetic fertilizer, manure, and sewage in the middle and lower reaches of the Beisha River. The nitrate was mainly derived from manure and sewage in the Nansha River. The nitrate was mainly derived from soil nitrogen in the upper reaches, mainly derived from synthetic fertilizer, manure, and sewage in the middle reaches, and mainly derived from manure and sewage in the lower reaches of the Haicheng River. During the wet season, the nitrate sources in surface water were soil nitrogen, synthetic fertilizer, manure, and sewage in the Beisha River; synthetic fertilizer, manure, and sewage in the middle and lower reaches of the Haicheng River and the Nansha River; and soil nitrogen and synthetic fertilizer in the upper reaches of the Haicheng River. NO3- and NH4+-N concentrations decreased with increasing △15 N-NO3- from the dry season to the wet season, indicating that volatilization of NH4+-N and denitrification of NO3- might occur during the wet season. There is a slightly positive relationship between the reciprocal of the concentration of 1/ρ(NO3-) and △15 N-NO3- during the wet season, indicating that mixing processes occurred in surface water. The results will provide information on nitrate sources during seasonal variations in the plain areas.

Geochemical analysis of sediments from a semi-enclosed bay (Dongshan Bay, southeast China) to determine the anthropogenic impact and source.

The geochemical compositions of sediments in the Dongshan Bay, a semi-enclosed bay on the southeast coast of China, were obtained to identify pollutant sources and evaluate the anthropogenic impacts over the last 100 years. The results indicated that the metal flux had been increasing since the 1980s. Enrichment factor values (Pb, Zn and Cu) suggested only slight enrichment. The proportion of anthropogenic Pb changed from 9% to 15% during 2000-2014. Coal combustion might be an important contamination source in the Dongshan Bay. The historical variation in the metal flux reflected the economic development and urbanization in the Zhangjiang drainage area in the past 30 years. According to the Landsat satellite remote sensing data, the urbanization area expanded approximately three times from 1995 to 2010. The δ13C values (-21‰ to -23‰) of the organic matter (OM) in the sediments indicated that the OM was primarily sourced from aquatic, terrigenous and marsh C3 plants. Nitrogen was mainly derived from aquatic plants and terrigenous erosion before the 1980s. However, the total organic carbon (TOC) contents, total nitrogen (TN) contents and δ15N had been increasing since the 1980s, which suggested that the sources of nitrogen were soil erosion, fertilizer and sewage. In addition, the TOC and TN fluxes in the Dongshan Bay had significantly increased since the 1980s, which reflected the use of N fertilizer. However, the TOC and TN fluxes significantly decreased in the past decade because environmental awareness increased and environmental protection policies were implemented.