15981. 题目: Contribution of the Excited Triplet State of Humic Acid and Superoxide Radical Anion to Generation and Elimination of Phenoxyl Radical
期刊: Environmental Science & Technology
作者: Yuan Chen, Xu Zhang, Shixiang Feng
摘要: Contributions of excited triplet state of humic acid (3HA*) and superoxide radical anion (O2 –), which is mainly generated via the reaction of O2 with HA-derived reducing intermediates (HA –), to phenol transformation were revealed using acetaminophen, 2,4,6-trimethylphenol and tyrosine as probe molecules. Phenol transformation was initiated by 3HA*, leading to the formation of the phenoxyl radical (PhO ), but the distribution of transformation intermediates was codetermined by 3HA* and HA –. The influence of HA – essentially resulted from the production of O2 –, which affected the fate of PhO . PhO could undergo dimerization, or react with O2 –, leading to either phenol peroxide formation (radical addition) or phenol regeneration (electron transfer). In addition, PhO could bind to HA or react with HA radicals, particularly in the absence of O2 and O2 –. These PhO reactions were dependent on the reduction potential and structure of PhO . This study also proved that the reaction of phenol with 1O2 and the reaction of PhO with O2 – lead to the same oxidation product. The contributions of 3HA* and its generated 1O2, HA – and its generated O2 – to phenol transformation were pH-dependent.
15982. 题目: Influence of pO2 on Iron Redox Cycling and Anaerobic Organic Carbon Mineralization in a Humid Tropical Forest Soil
期刊: Environmental Science & Technology
作者: Chunmei Chen, Christof Meile, Jared Wilmoth, Diego Barcellos, Aaron Thompson
摘要: Ferrous iron (FeII) oxidation is an important pathway for generating reactive FeIII phases in soils, which can affect organic carbon (OC) persistence/decomposition. We explored how pO2 concentration influences FeII oxidation rates and FeIII mineral composition, and how this impacts the subsequent FeIII reduction and anaerobic OC mineralization following a transition from oxic to anoxic conditions. We conducted batch soil slurry experiments within a humid tropical forest soil amended with isotopically labeled 57FeII. The slurries were oxidized with either 21% or 1% pO2 for 9 days and then incubated for 20 days under anoxic conditions. Exposure to 21% pO2 led to faster FeII oxidation rates and greater partitioning of the amended 57Fe into low-crystallinity FeIII-(oxyhydr)oxides (based on M ssbauer analysis) than exposure to 1% pO2. During the subsequent anoxic period, low-crystallinity FeIII-(oxyhydr)oxides were preferentially reduced relative to more crystalline forms with higher net rates of anoxic FeII and CO2 production—which were well correlated—following exposure to 21% pO2 than to 1% pO2. This study illustrates that in redox-dynamic systems, the magnitude of O2 fluctuations can influence the coupled iron and organic carbon cycling in soils and more broadly, that reaction rates during periods of anoxia depend on the characteristics of prior oxidation events.
15983. 题目: Overlooked Risks of Biochars: Persistent Free Radicals trigger Neurotoxicity in Caenorhabditis elegans
期刊: Environmental Science & Technology
作者: Thora Lieke, Xuchao Zhang, Christian E.W. Steinberg, and Bo Pan
摘要: In recent years, biochars have gained increasing interest in mitigating climate changes and revitalizing contaminated or drained soil. Studies determining their impact on the ecosystem, especially on soil invertebrates, however, are still scarce and the neurotoxic potential of biochars has never been evaluated before. Using the model organism Caenorhabditis elegans we determined the neurotoxic effect of biochar produced from rice straw by pyrolysis at 500 °C at concentrations ranging from 0 to 2000 mg C·L–1. Biochar had a hormetic effect on locomotion behavior. Furthermore, high concentrations impaired defecation as well as the recognition and response to a chemical attractant. None of the potential toxic chemicals in the biochar had sufficient high concentrations to explain the detected neurotoxic effect. Using electron paramagnetic resonance (EPR) spectroscopy, we detected free radicals in the biochar. Detrimental reaction of free radicals with biotic macromolecules can induce oxidative stress responses and are a potential reason for the evaluated neurotoxic effect of biochar. Overall, we were able to prove that biochars have the potential to act as weak neurotoxins to soil organisms and effects of persistent free radicals should be investigated further.
15984. 题目: δ13C of aromatic compounds in sediments, oils and atmospheric emissions: A review
期刊: Organic Geochemistry
作者: Alex I. Holman, Kliti Grice
摘要: This review discusses major applications of stable carbon isotopic measurements of aromatic compounds, along with some specific technical aspects including purification of aromatic fractions for baseline separation. δ 13C measurements of organic matter (OM) in sediments and oils are routine in all fields of organic geochemistry, but they are predominantly done on saturated compounds. Aromatic compounds are important contributors to sedimentary organic matter, and provide indication of diagenetic processes, OM source, and thermal maturity. Studies have found evidence for a small 13C-enrichment during diagenetic aromatisation of approximately 1–2‰, but the formation of polycyclic aromatic hydrocarbons (PAHs) from combustion and hydrothermal processes seems to produce no effect. Likewise, maturation and biodegradation also produce only small isotopic effects. An early application of δ 13C of aromatic compounds was in the classification of oil families by source. Bulk measurements have had some success in differentiating marine and terrigenous oils, but were not accurate in all settings. Compound-specific analyses measure certain aromatics with strong links to source, therefore allowing more accurate source identification. δ 13C measurements of individual aromatic compounds also allow identification of higher plant input in ancient sediments, even after severe diagenetic alteration or combustion to PAHs. Perylene, a PAH with a historically contentious origin, was assigned a source from wood-degrading fungi on the basis of its isotopic composition. Stable carbon isotopic measurements are also important in the analysis of organic matter from Chlorobiaceae, which is an important indicator of photic zone euxinic conditions in ancient sediments. A large range of aromatic products are formed from the carotenoid pigments of Chlorobiaceae, with an enriched carbon isotopic composition characteristic of the reverse tricarboxylic acid photosynthetic pathway employed by this family of organisms. In future, site-specific isotope analysis using techniques such as nuclear magnetic resonance spectrometry and high-resolution isotope ratio mass spectrometry may reveal more information about isotopic effects associated with aromatisation processes and maturation.
15985. 题目: Impact of dissolved organic matter on Zn extractability and transfer in calcareous soil with maize straw amendment
期刊: Journal of Soils and Sediments
作者: Yanlong Chen, Jianglan Shi, Xiaohong Tian, Zhou Jia, Shaoxia Wang, Juan Chen, Wenling Zhu
摘要: Purpose: Crop straw return into arable land is a common method of disposing of excess straw in China and can improve soil dissolved organic matter (DOM) that is known to modify soil zinc (Zn) extractability and mobility. Materials and methods: We conducted a soil box (internal dimensions, 160 × 140 × 80 mm3) experiment to evaluate the response of Zn extractability and transfer by diffusion to DOM after maize straw amendment (St, 0 and 15 g kg 1) in calcareous soil treated with ZnSO4·7H2O (Zn, 0 and 20 mg kg 1). Soil treated with St0Zn0 (control), St15Zn0, St0Zn20, or St15Zn20 was isolated in the 10-mm center of the box, and untreated soil was placed in compartments at either side. Results and discussion: Results revealed that addition of St0Zn20 or St15Zn20 increased the concentration of Zn extracted with diethylenetriaminepentaacetic acid (DTPA-extractable Zn) in the central layer compared with control or addition of St15Zn0. Over the course of 45 days, transfer of DTPA-extractable Zn into the adjacent untreated soil was detected at 15–20 mm in soil with St15Zn20 but at 10–15 mm with St0Zn20 and only 0–5 mm with St15Zn0. Additionally, a higher amount of DTPA-extractable Zn transfer into the adjacent untreated soil also occurred in St15Zn20. This increased DTPA-extractable Zn transfer may be associated with the formation of Zn-fulvic acid complexes with the provision of DOM derived from straw. Conclusions: Soluble Zn combined with straw return may be a promising strategy for improving both Zn mobility and extractability in calcareous soil.
15986. 题目: Scrutiny of interference effect of ions and organic matters on water treatment using supported nanoscale zero-valent iron
期刊: Environmental Earth Sciences
作者: Ahmed M. E. Khalil, Osama Eljamal, Tareq W. M. Amen, Yuji Sugihara, Nobuhiro Matsunaga
摘要: Nanoscale zero-valent iron (nZVI) supported on heat-modified activated charcoal (nFe(0)/AC) can improve nitrate reduction and phosphate adsorption regarding reaction conversion, adsorption capacity, and kinetics. It is more effective in terms of mobility and stability than bare nZVI. Both nZVI and its supported type were synthesized, characterized, and examined in interference studies for applications in environmental remediation technologies. Solutions of 45.18 mg nitrate–N/L, 50 mg phosphorus/L, and a mixture of them were treated using nZVI and nFe(0)/AC in municipal wastewater body and also deionized water body in the coexistence of anions (phosphate and sulfate), cations (cuprous and cupric), organic matters (humic acid), and hardness (calcium carbonates) at different concentrations. Results showed the significant impact of interference on nitrate reduction and superiority of nFe(0)/AC by ca. 27% to ca. 183% increase in treatment efficiency over nZVI. Anions were easily attracted to the surface of nano-iron particles resulting in a negative intervening effect. Hardness and contaminants of municipal wastewater provided a negative impact and significantly interfered with nitrate removal, while organic matters had a lower negative interference compared to others. On the contrary, copper cations could improve removal efficiency until complete elimination of nitrate. The experimental data were best-fitted to a kinetic rate model that combined the pseudo-first-order rate with the deactivation rate arising from the passivation of interfering substances on the surface of nZVI-based materials. The value of parameters of this rate equation could estimate the degree and type of interference occurring during nitrate decontamination.
15987. 题目: Soil erosion and chemical weathering in a region with typical karst topography
期刊: Environmental Earth Sciences
作者: Kai Xiong, Chuan Yin, Hongbing Ji
摘要: Soil erosion is a global environmental issue that can lead to the loss of nutrient-rich topsoil and even soil desertification, which is more severe in vulnerable and sensitive karst areas. Currently, it is imperative to explore the soil erosion mechanism and the weathering process to help prevent soil degradation in the karst area. In this study, we estimated the soil erosion rate of a representative karst slope in Shilin area of China by 137Cs tracer method. We also analyzed the changes of soil total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) along the soil profiles. The results show that there is mild to moderate intensity erosion in this area, and erosion rates in different locations of slope are in the following order: hilltop > hillside > bottom. The 137Cs content has a certain correlation with TOC, TN and TP content in the soil profile, which indicates they may have similar loss pathways. Furthermore, the chemical index of alteration (CIA), Na/K value and their relation with soil erosion are analyzed and reveal that the studied area is seriously affected by physical erosion and chemical weathering under a hot and humid environment area.
15988. 题目: Efficient capture of aqueous humic acid using a functionalized stereoscopic porous activated carbon based on poly(acrylic acid)/food-waste hydrogel
期刊: Journal of Environmental Sciences
作者: Tao Zhou, Xin Zhao, Shuya Wu, Lianghu Su, Youcai Zhao
摘要: Stereoscopic porous carbons have shown good potential in humic acid (HA) removal. In this work, a novel stereoscopic porous activated carbon (SPAC) was designed and synthesized via the self-assembly of a hydrogel based on food waste during in-situ polymerization, vacuum drying, carbonization, and activation. Then, the SPAC was functionalized with 3-aminopropyltriethoxysilane (APTES) and the adsorption behavior of the modified SPAC (SPAC-NH2) was studied systematically. The effects of pH, contact time, initial concentration of HA, and adsorbent dose were investigated, showing that optimal HA removal efficiency (>98.0%) could be achieved at an initial HA concentration of 100 mg/L. The experimental adsorption isotherm data was fitted to the Langmuir model with a maximum adsorption capacity of 156.0 mg HA/g SPAC-NH2. Analysis of the mechanism indicated that the removal of HA was mainly realized through the amidization reaction between the COOH groups of HA and the NH2 groups of APTES. All of the above results showed that SPAC-NH2 powder is an efficient, eco-friendly, and reusable adsorbent which is suitable for the removal of HA from wastewater.
15989. 题目: Carbon dynamics and inconstant porewater input in a mangrove tidal creek over contrasting seasons and tidal amplitudes
期刊: Geochimica et Cosmochimica Acta
作者: Pierre Taillardat, Alan D. Ziegler, Daniel A. Friess, David Widory, Vinh Truong Van, Frank David, Nguy?n Thành-Nho, Cyril Marchand
摘要: Constraining the contribution of mangrove-derived carbon in tidal creeks is fundamental to understanding the fate of mangrove primary production and the role of mangroves as coastal carbon sinks. Porewater measurements and 24-h time series in a mangrove tidal creek were conducted during the dry and wet season, and over contrasting tidal ranges at the Can Gio Biosphere Reserve, Vietnam. Surface water carbon concentrations (dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), partial pressure of carbon dioxide (pCO2)) and their respective δ13C values were correlated with radon, suggesting that porewater input drives mangrove-derived carbon in the tidal creek. Based on three complementary mixing models, porewater input contributed to about 30% of the water volume and 46% to 100% of DOC and DIC pools in the tidal creek at low tide, with variabilities between seasons and tidal amplitudes. The creek carbon pool was 88% DIC, 6% DOC, and 6% particulate organic carbon (POC). The pCO2 values during the wet season (2973–16,495 μatm) were on average 5-fold higher than during the dry season (584–2946 μatm). This was explained by a potential greater mineralization attributed to higher organic matter availability and residual humidity that stimulate bacterial activity, and by a potential tidal dilution changing the pCO2/DIC ratio as suggested by the Revelle factor. Consequently, average CO2 evasion from the creek was estimated at 327–427 mmolC m 2 d 1 during the wet season and 92–213 mmolC m 2 d 1 during the dry season, using two independent approaches. Tidal amplitude seemed to influence porewater input and its carbon loads, with a higher contribution during frequent and high tidal amplitudes (symmetric). However, the highest input occurred in a tidal cycle which was preceded by tidal cycle of low amplitude (asymmetric). We explain this ambiguity by the influence of both, rapid water turnover intensifying porewater exchange, and long water residence time enhancing carbon load in porewater.
15990. 题目: Redox-influenced trace element compositional differences among variably aqueously altered CM chondrites
期刊: Geochimica et Cosmochimica Acta
作者: Jon M. Friedrich, Neyda M. Abreu, Stephen F. Wolf, Julianne M. Troiano, Gregory L. Stanek
摘要: It is generally agreed that the CM chondrites are remarkably compositionally uniform. To date, this observation has largely been based on major and selected trace element bulk elemental abundances. Here, we examine the trace element compositional uniformity of the CM chondrites in detail. We quantified the abundances of 43 trace elements in 21 CM chondrites displaying variable degrees of petrographically identified aqueous alteration. With these data, we used graphic and standard statistical methods for examining evidence for compositional differences with respect to degree of aqueous alteration. The results show that suites of variably aqueously altered CM chondrites have readily apparent and statistically significant trace element compositional differences. Higher degrees of aqueous alteration are associated with depleted bulk trace elemental abundances; however, when the variable mineralogy and hydration (H2O or OH) are taken into account, the compositional differences between variably aqueously altered suites of CM chondrites largely disappear. Nevertheless, some trace elements still show statistically significant differences between suites of CM chondrites that experienced extensive and milder degrees of aqueous alteration. These elements are observed to be redox sensitive species (e.g. Mn, Zn, Mo, Re, U), whose mobilities between aqueous solutions and solids are mediated by complex ions whose solubilities are sensitive to a complicated combination of either the presence of Mn or Fe (oxy)hydroxide surfaces, specific redox environments, solution pH, presence of organic matter, and phyllosilicate surface binding. The studies suggest that the apparent compositional differences of these elements reflect an evolving redox environment during the history of the CM chondrites. It is unclear if the compositional differences between variably aqueously altered CM chondrites are the result of anisochemical (open system) aqueous alteration for some redox condition sensitive trace elements on the CM parent body or bodies or if the differences are the result of the meteorites’ terrestrial residence.
15991. 题目: Silicon regulation of soil organic carbon stabilization and its potential to mitigate climate change
期刊: Earth-Science Reviews
作者: Zhaoliang Song, Congqiang Liu, Karin Müller, Xiaomin Yang, Yuntao Wu, Hailong Wang
摘要: The terrestrial biogeochemical silicon (Si) cycle may significantly influence the stabilization of soil organic carbon (SOC), and thus plays an important role in regulating the global carbon (C) balance and climate change. Processes involved in Si-enhanced SOC stability at a decadal or centennial scale include protection of SOC through amorphous Si and interactions of Si-iron (Fe) and Si-aluminum (Al). Strategic manipulation of the Si cycle in terrestrial ecosystems offers a new opportunity to enhance soil C sequestration. Rock powder amendment, establishment of Si-rich plant buffer strips and innovative management practices that return Si-rich biomass materials to soil can be implemented as strategies to enhance soil C sequestration through regulating the terrestrial Si cycle. However, quantifying (i) the contribution of different processes to enhance soil dissolved Si and secondary Si minerals, (ii) the relative importance of different SOC stabilization mechanisms, and (iii) the potential and cost of different measures has not been attempted.
15992. 题目: Preliminary studies on the impact of in situ oil sand extraction methods on the movement of water soluble organics and inorganics by a pilot scale test
期刊: Environmental Science: Water Research & Technology
作者: Xiaomeng Wang, Kim Kasperski, Amanda Cook, Adrian Ilko
摘要: The oil sands of Alberta, Canada constitute the world's largest bitumen reserve. In situ extraction methods are used to recover deeper bitumen resources. Thermal methods are commonly used, for which, steam is generated on the surface and injected underground to heat the reservoir, and thereby improve the flow of the bitumen. The overall objective of this study was to understand what happens to the chemistry of water that is pumped down as steam into an oil sand formation during in situ thermal recovery operations, as well as to the water that is already in the formation as groundwater. In this paper, apparatus has been designed on a pilot scale and used to study mineral–water reactions at the temperatures and pressures observed underground in a steam chamber formed during in situ oil sand operations with a focus on both soluble organics and inorganics. The results showed that there were reactions occurring between the minerals and water as evidenced by the change in anion concentration, pH and pE of the aqueous solutions. This pilot scale study demonstrates that the underground inorganic and organic water chemistry could change during the high-temperature thermal in situ oil sand extraction process.
15993. 题目: Substrate identity and amount overwhelm temperature effects on soil carbon formation
期刊: Soil Biology and Biochemistry
作者: Emily E. Oldfield, Thomas W. Crowther, Mark A. Bradford
摘要: The size of the soil carbon sink depends on the balance between soil organic matter (SOM) formation and decomposition. Our understanding of how SOM forms and is stabilized, however, is shifting. Traditional theory maintains the formation of SOM is due to chemical complexity: difficult to decompose plant inputs persist in the soil while easily decomposable inputs are respired as CO2. However, consensus is now building around an alternative thesis, hypothesizing that the plant inputs most easily assimilated by soil decomposers are the ones stabilized as SOM because dead microbial biomass is now considered one of the primary components of stable SOM. As such, the efficiency with which the microbial community uses these plant inputs has direct implications for the amount and rate of SOM formation under both a constant and changing climate. Our study empirically tests and measures the effects of substrate quality, quantity, and temperature on SOM formation rates – a process that may have profound impact on carbon stocks. We used 13C-labeled substrates representative of plant root exudates (simple sugars, amino acids, and organic acids) to determine the proportion of substrate retained within SOM, microbial biomass, dissolved organic carbon, or evolved as 13CO2. We found that glucose, the substrate most efficiently assimilated by the microbial biomass, leads to the greatest amount of SOM formation compared to glycine and oxalic acid. In contrast to expectations, higher concentrations of substrate addition lead to proportionally less 13C label retention than lower concentrations. Temperature had a negligible impact on SOM formation, with higher temperatures actually leading to slight increases in SOM formation. While substrate quality and quantity drove the largest differences in SOM formation rates, once metabolized by the microbial biomass, eventual incorporation of carbon into the mineral associated SOM pool (thought to be the most stable of the soil C pools), was effectively equivalent across treatments. Our data suggest that changing composition and amount of labile carbon substrates supplied to soils will likely be key determinants of SOM formation rates and, hence, potentially soil carbon stock sizes.
15994. 题目: Temperature effects on structure and function of the methanogenic microbial communities in two paddy soils and one desert soil
期刊: Soil Biology and Biochemistry
作者: Pengfei Liu, Melanie Klose, Ralf Conrad
摘要: Temperature is an important factor regulating the production of the greenhouse gas CH4. Previous studies of temperate methanogenic paddy soils from Italy showed that structure and function of the soil microbial communities changed drastically when temperature was increased to values higher than about 40 °C. Since methanogenic archaea are ubiquitous in both wetland and upland soils, we wondered whether other soils would behave similarly. Therefore, we compared paddy soils from Italy and the Philippines, which have different microbial community structures, and also investigated a desert soil from Utah (USA), which expressed CH4 production upon flooding. We incubated these soils under anoxic conditions at three different temperatures. We determined composition, abundance and function of the methanogenic archaeal and bacterial communities using illumina HiSeq sequencing, qPCR and analysis of activity and stable isotope fractionation, respectively. At moderate temperatures (25 °C and 35 °C), CH4 was always produced by a combination of acetoclastic and hydrogenotrophic methanogenesis. However, at elevated temperature (45 °C) the combination of acetoclastic and hydrogenotrophic methanogenesis was only maintained in the Philippines soil, which contained hydrogenotrophic (Methanobacteriales, Methanocellales, Methanosarcinaceae) and acetoclastic (Methanosarcinaceae, Methanotrichaceae) methanogenic taxa under these conditions. In Italian and Utah soil by contrast, CH4 production at 45 °C occurred by hydrogenotrophic methanogenesis, and the archaeal community was lacking acetoclastic methanogens. Acetate was instead oxidized by Thermoanaerobacteraceae (and perhaps Heliobacteriaceae) affiliated species which were syntrophically connected to hydrogenotrophic Methanocellales and Methanobacteriales. Our results showed that the different soils exhibited different structures and functions of the methanogenic archaeal and bacterial communities at elevated versus moderate temperatures. While acetoclastic methanogens in the Philippines paddy soil were able to tolerate elevated temperatures, those in Italian paddy soil and Utah desert soil were not. Instead, syntrophic acetate oxidation allowed the complete degradation of organic matter to CH4 and CO2.
15995. 题目: Properties of seawater neutralized bauxite residues and changes in chemical, physical and microbial properties induced by additions of gypsum and organic matter
期刊: Journal of Environmental Management
作者: Yaying Li, Richard J. Haynes, Irena Chandrawana, Ya-Feng Zhou
摘要: Seawater neutralization is a technique that can be used to treat bauxite residue prior to its storage but, as yet, no attempts have been made to revegetate it. Seawater neutralized bauxite residue was found to have a pH1:5 of 9.3 and to be highly saline (EC1.5 16.5 dS m 1). After leaching pH1:5 rose to 9.7 and the residue was still highly sodic (ESP = 64–69%). Addition of 1% gypsum, prior to leaching, arrested this increase in pH while with 5% gypsum addition the pH1:5 was lowered to 8.9. Addition of 5% gypsum also reduced ESP to 38% and increased watercress germination in the residue from 58% in control treatments to 88%. The major ions in leachates were Na+ and Cl and gypsum application increased the quantities of Na+, Ca2+ and SO4 2 leached. Addition of 6% biosolids or 6% poultry manure added exchangeable cations to the mud and lowered ESP by 5–11%.The EC was 2.8–3.7 (mean 3.1) times higher and pH 0.2–0.7 (mean 0.43) units lower in saturation paste compared with 1:5 soil:water extracts. Addition of amendments had only small effects on physical properties. While organic C content was increased more by biosolids than poultry manure addition the reverse was the case for soluble organic C, microbial biomass C and basal respiration. It was concluded that although seawater neutralization initially lowers the pH of bauxite residues it is unlikely to increase the ease with which they can be revegetated.
15996. 题目: Amino sugars as specific indices for fungal and bacterial residues in soil
期刊: Biology and Fertility of Soils
作者: Rainer Georg Joergensen
摘要: Amino sugars are important indices for the contribution of soil microorganisms to soil organic matter. Consequently, the past decade has seen a great increase in the number of studies measuring amino sugars. However, some uncertainties remain in the interpretation of amino sugar data. The objective of the current opinion paper is to summarize current knowledge on amino sugars in soils, to give some advice for future research objectives, and to make a plea for the correct use of information. The study gives an overview on the origin of muramic acid (MurN), glucosamine (GlcN), galactosamine (GalN), and mannosamine (ManN). Information is also provided on measuring total amino sugars in soil but also on compound-specific δ13C and δ15N determination. Special attention is given to the turnover of microbial cell-wall residues, to the interpretation of the GlcN/GalN ratio, and to the reasons for converting fungal GlcN and MurN to microbial residue C. There is no evidence to suggest that the turnover of fungal residues generally differs from that of bacterial residues. On average, MurN contributes 7% to total amino sugars in soil, GlcN 60%, GalN 30%, and ManN 4%. MurN is highly specific for bacteria, GlcN for fungi if corrected for the contribution of bacterial GlcN, whereas GalN and ManN are unspecific microbial markers.
15997. 题目: Distribution and thermal stability of physically and chemically protected organic matter fractions in soils across different ecosystems
期刊: Biology and Fertility of Soils
作者: Beatrice Giannetta, César Plaza, Costantino Vischetti, M. Francesca Cotrufo, Claudio Zaccone
摘要: Accrual of carbon (C) and nitrogen (N) in soil is a significant and realizable management option to mitigate climate change; thus, a clear understanding of the mechanisms controlling the persistence of C and N in soil organic matter (SOM) across different ecosystems has never been more needed. Here, we investigated SOM distribution between physically and chemically stabilized fractions in soils from a variety of ecosystems (i.e., coniferous and broadleaved forest soils, grassland soils, technosols, and agricultural soils). Using elemental and thermal analyses, we examined changes in the quantity and quality of physically fractionated SOM pools characterized by different mechanisms of protection from decomposition. Independently of the ecosystem type, most of the organic C and total N were found in the mineral-associated SOM pool, known to be protected mainly by chemical mechanisms. Indexes of thermal stability and C/N ratio of this heavy SOM fraction were lower (especially in agricultural soils) compared to light SOM fractions found free or occluded in aggregates, and suggested a marked presence of inherently labile compounds. Our results confirm that the association of labile organic molecules with soil minerals is a major stabilization mechanism of SOM, and demonstrate that this is a generalizable finding occurring across different mineral soils and ecosystems.
15998. 题目: Microbial CO 2 assimilation is not limited by the decrease in autotrophic bacterial abundance and diversity in eroded watershed
期刊: Biology and Fertility of Soils
作者: Haibing Xiao, Zhongwu Li, Xiaofeng Chang, Lei Deng, Xiaodong Nie, Chun Liu, Lin Liu, Jieyu Jiang,Jia Chen, Danyang Wang
摘要: The impacts of soil erosion on soil structure, nutrient, and microflora have been extensively studied but little is known about the responses of autotrophic bacterial community and associated carbon (C)-fixing potential to soil erosion. In this study, three abandoned croplands (ES1, ES2, and ES3) and three check dams (DS1, DS2, and DS3) in the Qiaozi watershed of Chinese Loess Plateau were selected as eroding sites and depositional sites, respectively, to evaluate the impacts of soil erosion on autotrophic bacterial community and associated C-fixing potential. Lower abundance and diversity of autotrophic bacteria were observed in nutrient-poor depositional sites compared with nutrient-rich eroding sites. However, the relative abundances of obligate autotrophic bacteria, such as Thiobacillus and Synechococcus, were significantly enhanced in depositional sites. Deposition of nutrient-poor soil contributed to the growth of obligate autotrophic bacteria. The maximum microbial C-fixing rate was observed in DS1 site (5.568 ± 1.503 Mg C km 2 year 1), followed by DS3 site (5.306 ± 2.130 Mg C km 2 year 1), and the minimum was observed in ES2 site (0.839 ± 0.558 Mg C km 2 year 1). Soil deposition significantly enhanced microbial C-fixing rate. Assuming a total erosion area of 1.09 × 107 km2, microbial C-fixing potential in eroded landscape can range from 0.01 to 0.06 Pg C year 1. But its effect on the C pool recovery of degraded soil is limited. Dissolved organic C (DOC) was the main explanatory factor for the variation in soil microbial C-fixing rate (72.0%, P = 0.000).
15999. 题目: Soil carbon storage predicted from the diversity of pyrolytic alkanes
期刊: Biology and Fertility of Soils
作者: Marco A. Jiménez-González, Ana M. ?lvarez, Zulimar Hernández, Gonzalo Almendros
摘要: Biogeochemical factors responsible of the highly variable content of soil organic matter (SOM) in the different types of soils are poorly known. In particular, the role of organo-mineral interactions has frequently been considered, but less attention has been paid to the molecular composition of the SOM. The aim of this work was to contribute to a better qualitative and quantitative assessment of the soil organic C (SOC) accumulation, using chemometric approaches that do not require the absolute knowledge of the structure and functioning of the whole system under study. For this reason, we monitored the n-alkanes released by analytical pyrolysis from 35 widely different Mediterranean soils. The H′ Shannon diversity index was calculated to evaluate the origin and transformations of the alkane homologous series (C9–C31). A series of multivariate data treatments succeeded in showing significant relationship between the diversity of alkanes and the SOC concentration, and additional indicators of SOM quality were also used. All statistical analyses pointed out the significant correlation (P < 0.01) between the H′ diversity of the pyrolytic alkanes and the amount of SOC. In particular, a significant relationship between SOC levels and the percentage of long-chain alkanes was found, whereas the percentage of short-chain alkanes was correlated with specific descriptors of SOM quality. Finally, the partial least squares (PLS) predicted the SOC content from the alkane patterns.
16000. 题目: Longitudinal trends in concentration and composition of dissolved organic nitrogen (DON) in a largely unregulated river system
作者: Clayton W. Harris, Gavin N. Rees, Rick J. Stoffels, John Pengelly, Kirsten Barlow, Ewen Silvester
摘要: Dissolved organic nitrogen (DON) can comprise up to 80% of the dissolved N pool in riverine ecosystems, but concentration and compositional responses to catchment conditions has received limited attention. We examined the suite of nitrogenous nutrients along the length of the Ovens River, Victoria, Australia, a river with identifiable regions of native vegetation, agricultural activity and floodplain forest connection, carrying out longitudinal surveys in winter during a period of high flow and in summer during a period of stable base flow. We examined: the concentrations of DON, the proportion of DON that occurs as dissolved combined amino acids (DCAAs), whether concentration and DCAA composition varied between flow and whether land-use and tributaries have an impact upon nutrient concentration and DON composition. DON concentrations were greater than dissolved inorganic nitrogen under both base flow and high flow conditions. Under base flow DON exhibited a continuous increase in concentration downstream (ranging from 50 to 300 μg/L), compared to a much larger increase under high flow (150–600 μg/L) coupled with a major discrete increase of ~ 350 μg/L at a tributary input (King River). Concentrations of NOx (oxides of nitrogen) species were much higher under high flow conditions (range 50–250 μg/L) compared to 0–50 g/L at base flow, and showed a significant increase in concentration with distance downstream. A discrete change in NOx concentrations was also observed at the King River confluence under high flow, although in this case causing a decrease in concentration of ~100 g/L. DCAA concentrations varied little along the length of the river at base flow but increased with distance downstream at high flow. The DCAA concentrations were of the same order of magnitude as ammonium at both base and high flows and nitrate concentrations at base flow. The proportion of DON that was in the form of DCAA was reasonably uniform during high flow (3–6%), but highly variable at base flow (5–44%). The amino acid (AA) composition of the DCAA varied along the river and differed between flow regimes (except below the confluence with the King River where AA composition under the two flow conditions converged) suggesting a strong influence of land use. We show that DON is potentially a large component (4–81%) of the total N budget and given that 5–23% is in the form of peptide/protein, represents an important source of N. DON and more specifically DCAAs should therefore be considered both when constructing N budgets and monitoring levels of in-stream nitrogen.