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23421. 题目: Carbon dynamics and inconstant porewater input in a mangrove tidal creek over contrasting seasons and tidal amplitudes
文章编号: N18070121
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
更新时间: 2018-07-01
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.

23422. 题目: Redox-influenced trace element compositional differences among variably aqueously altered CM chondrites
文章编号: N18070120
期刊: Geochimica et Cosmochimica Acta
作者: Jon M. Friedrich, Neyda M. Abreu, Stephen F. Wolf, Julianne M. Troiano, Gregory L. Stanek
更新时间: 2018-07-01
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.

23423. 题目: Silicon regulation of soil organic carbon stabilization and its potential to mitigate climate change
文章编号: N18070119
期刊: Earth-Science Reviews
作者: Zhaoliang Song, Congqiang Liu, Karin Müller, Xiaomin Yang, Yuntao Wu, Hailong Wang
更新时间: 2018-07-01
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.

23424. 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
文章编号: N18070118
期刊: Environmental Science: Water Research & Technology
作者: Xiaomeng Wang, Kim Kasperski, Amanda Cook, Adrian Ilko
更新时间: 2018-07-01
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.

23425. 题目: Substrate identity and amount overwhelm temperature effects on soil carbon formation
文章编号: N18070117
期刊: Soil Biology and Biochemistry
作者: Emily E. Oldfield, Thomas W. Crowther, Mark A. Bradford
更新时间: 2018-07-01
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.

23426. 题目: Temperature effects on structure and function of the methanogenic microbial communities in two paddy soils and one desert soil
文章编号: N18070116
期刊: Soil Biology and Biochemistry
作者: Pengfei Liu, Melanie Klose, Ralf Conrad
更新时间: 2018-07-01
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.

23427. 题目: Properties of seawater neutralized bauxite residues and changes in chemical, physical and microbial properties induced by additions of gypsum and organic matter
文章编号: N18070115
期刊: Journal of Environmental Management
作者: Yaying Li, Richard J. Haynes, Irena Chandrawana, Ya-Feng Zhou
更新时间: 2018-07-01
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.

23428. 题目: Amino sugars as specific indices for fungal and bacterial residues in soil
文章编号: N18070114
期刊: Biology and Fertility of Soils
作者: Rainer Georg Joergensen
更新时间: 2018-07-01
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.

23429. 题目: Distribution and thermal stability of physically and chemically protected organic matter fractions in soils across different ecosystems
文章编号: N18070113
期刊: Biology and Fertility of Soils
作者: Beatrice Giannetta, César Plaza, Costantino Vischetti, M. Francesca Cotrufo, Claudio Zaccone
更新时间: 2018-07-01
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.

23430. 题目: Microbial CO 2 assimilation is not limited by the decrease in autotrophic bacterial abundance and diversity in eroded watershed
文章编号: N18070112
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
更新时间: 2018-07-01
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).

23431. 题目: Soil carbon storage predicted from the diversity of pyrolytic alkanes
文章编号: N18070111
期刊: Biology and Fertility of Soils
作者: Marco A. Jiménez-González, Ana M. ?lvarez, Zulimar Hernández, Gonzalo Almendros
更新时间: 2018-07-01
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.

23432. 题目: Longitudinal trends in concentration and composition of dissolved organic nitrogen (DON) in a largely unregulated river system
文章编号: N18070110
期刊: Biogeochemistry
作者: Clayton W. Harris, Gavin N. Rees, Rick J. Stoffels, John Pengelly, Kirsten Barlow, Ewen Silvester
更新时间: 2018-07-01
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.

23433. 题目: Minerals in the rhizosphere: overlooked mediators of soil nitrogen availability to plants and microbes
文章编号: N18070109
期刊: Biogeochemistry
作者: Andrea Jilling, Marco Keiluweit, Alexandra R. Contosta,Serita Frey, Joshua Schimel, J?rg Schnecker, Richard G. Smith, Lisa Tiemann, A. Stuart Grandy
更新时间: 2018-07-01
摘要: Despite decades of research progress, ecologists are still debating which pools and fluxes provide nitrogen (N) to plants and soil microbes across different ecosystems. Depolymerization of soil organic N is recognized as the rate-limiting step in the production of bioavailable N, and it is generally assumed that detrital N is the main source. However, in many mineral soils, detrital polymers constitute a minor fraction of total soil organic N. The majority of organic N is associated with clay-sized particles where physicochemical interactions may limit the accessibility of N-containing compounds. Although mineral-associated organic matter (MAOM) has historically been considered a critical, but relatively passive, reservoir of soil N, a growing body of research now points to the dynamic nature of mineral-organic associations and their potential for destabilization. Here we synthesize evidence from biogeoscience and soil ecology to demonstrate how MAOM is an important, yet overlooked, mediator of bioavailable N, especially in the rhizosphere. We highlight several biochemical strategies that enable plants and microbes to disrupt mineral-organic interactions and access MAOM. In particular, root-deposited low-molecular-weight exudates may enhance the mobilization and solubilization of MAOM, increasing its bioavailability. However, the competitive balance between the possible fates of N moers—bound to mineral surfaces versus dissolved and available for assimilation—will depend on the specific interaction between mineral properties, soil solution, mineral-bound organic matter, and microbes. Building off our emerging understanding of MAOM as a source of bioavailable N, we propose a revision of the Schimel and Bennett (Ecology 85:591–602, 2004) model (which emphasizes N depolymerization), by incorporating MAOM as a potential proximal mediator of bioavailable N.

23434. 题目: A quantitative method for the high throughput screening for the soil adhesion properties of plant and microbial polysaccharides and exudates
文章编号: N18070108
期刊: Plant and Soil
作者: Jumana Akhtar,Andrew F. Galloway,Georgios Nikolopoulos,Katie J. Field,Paul Knox
更新时间: 2018-07-01
摘要: Background and aims: Understanding the structures and functions of carbon-based molecules in soils is an important goal in the context of soils as an ecosystem function of immense importance. Polysaccharides are implicated in maintaining soil aggregate status but have not been extensively dissected in terms of their structures and soil adhesion properties. This is largely because of the technical difficulties in identifying polysaccharide structures and quantifying any functional properties.Methods: Here, we describe the use of a novel nitrocellulose-based adhesion assay to determine the relative capacities for soil adhesion of over twenty plant and microbial polysaccharides that are likely to be present in soil and to contribute to organic matter content and properties. Weights of soil adhered to spots of known amounts of specific polysaccharides were quantified by scanning of the nitrocellulose sheets.Results: The most effective polysaccharides identified from this survey included chitosan, β-1,3-glucan, gum tragacanth, xanthan and xyloglucan. We also demonstrate that the soil adhesion assay is suitable to assess the soil-binding properties of plant exudates.Conclusions: The soil adhesion assay will be useful for the functional dissection of the organic matter components of soils and also of the factors involved in soil attachment to plant roots and in rhizosheath formation.

23435. 题目: Effects of snow depth on acid-unhydrolyzable residue and acid-hydrolyzable carbohydrates degradation rates during foliar litter decomposition of Pinus koraiensis and Quercus mongolica
文章编号: N18070107
期刊: Plant and Soil
作者: Qiqian Wu
更新时间: 2018-07-01
摘要: Background and aims: Differences in snow depth induced by climate change alter the microenvironments under snowpack, which affect litter decomposition. The degradation of acid-unhydrolyzable residue (AUR) and acid-hydrolyzable carbohydrates (ACID) is a key factor controlling soil organic matter formation. However, how snow depth affects the degradation is poorly understood.Methods: A snow depth manipulation experiment with snow-addition, snow-removal, and control treatments was conducted in Northeast China. Foliar litter of Pinus koraiensis and Quercus mongolica was placed on top of the ground in each treatment and sampled for six times from November 2014 to October 2015.Results: AUR and ACID degradation rates decreased with the reduction of snow depth during the snow-covered season because of the insulating effect provided by snowpack; this relationship was reversed during the snow-free season due to more labile carbon remaining after the snowmelt. During the snow-covered season, AUR and ACID degradation rates were positively correlated to the sum of degree days above 0 °C. In contrast, AUR and ACID degradation rates were positively correlated with litter microbial biomass carbon during the snow-free season.Conclusions:Snow depth plays an important role in determining litter AUR and ACID degradation rates, but the effects on degradation rates differed between the snow-covered and snow-free seasons.

23436. 题目: Biochar application as a soil amendment for decreasing cadmium availability in soil and accumulation in Brassica chinensis
文章编号: N18070106
期刊: Journal of Soils and Sediments
作者: Yuxue Liu, Yuying Wang, Haohao Lu,Linson Lonappan, Satinder Kaur Brar,Lili He,Jinyuan Chen, Shengmao Yang
更新时间: 2018-07-01
摘要: Purpose: Biochar has emerged as a promising material for limiting the bioavailability of potentially toxic elements in contaminated soils. Despite the benefits associated with the agricultural use of biochar, there is minimal information available on biochar amendment of Cd accumulation in leafy vegetable cultivars.Materials and methods: A pot experiment was carried out to evaluate the feasibility of bamboo biochar (BB) and rice straw biochar (RSB) for decreasing cadmium (Cd) availability in artificially contaminated (Cd at 50 mg kg 1) soil, and its accumulation in Brassica chinensis. Biochar was applied at 0 (control), 0.5, 1, 2.5, and 5% (w/w).Results and discussion: RSB at 5% significantly reduced the availability of Cd in soil (by 19.3%) compared with BB (by 8.6%). Application of BB and RSB at 1–5% markedly enhanced soil pH by 1.17–5.48 and 2.47–7.46%, respectively. Moreover, soil organic carbon was improved by 40.3–155 and 22.2–111% with 1–5% BB and RSB amendment, respectively. Soil total N was significantly increased by 24.5 and 31.1% with 5% BB and RSB application, respectively. Soil available P was increased by 10.8–24.4 and 14.6–30.7% with 2.5–5% BB or RSB amendment, respectively. Application of 2.5–5% BB and RSB significantly increased soil available K by 76.8–291 and 203–627%, respectively. Biochar at 2.5–5% ratio significantly improved nutrient (P and K) uptake in B. chinensis. Furthermore, biochar was more effective at higher rates, and RSB performed better than BB as a soil nutrient supplement. Cd accumulation in B. chinensis was significantly reduced by 12.0–48.3 and 17.0–35.4% with 0.5–5% BB and 1–5% RSB amendment, respectively. Greater biochar application further decreased bioconcentration factor (BCF) in harvested B. chinensis (all values < 1). Incorporation of 5% BB and RSB significantly reduced BCF by 51.0 and 40.6%, respectively.Conclusions:Our results suggest that BB and RSB, especially at higher rates (> 2.5%), could be recommended as safe amendments for the immobilization of Cd in contaminated agricultural soils, thereby decreasing its threat to the food chain and human health.

23437. 题目: Cadmium bioavailability well assessed by DGT and factors influencing cadmium accumulation in rice grains from paddy soils of three parent materials
文章编号: N18070105
期刊: Journal of Soils and Sediments
作者: Dongqin Li, Wenyan Li, Qin Lu, Yongtao Li, Ning Li, Huijuan Xu, Zongling Ren, Yulong Zhang, Jinjin Wang
更新时间: 2018-07-01
摘要: Purpose:High Cd resulted from natural background or agricultural activities in some of the paddy soils in South China is a concern. It is imperative to understand the relationship between Cd bioavailability in high Cd soils and Cd accumulation in rice grains. Therefore, our objectives are to explore the relationship between Cd accumulation in rice grains and Cd availability which was characterized with five different methods, and to investigate factors influencing Cd accumulation in rice.Materials and methods: One hundred and twenty-two paired soil and rice plant samples were collected from paddy fields of three parent materials (sandshale, limestone, and Quaternary red earth) in Guangxi Province. Soil Cd availability was assessed using three chemical extractants (0.43 M HNO3, 0.01 M CaCl2, and 0.005 M DTPA) and compared with Cd in soil solution and that sampled by the diffusive gradients in thin films (DGT) method. A five-step sequential fractionation of Cd was also carried out. Random forest (RF) was employed for assessing factor relative importance in Cd accumulation in rice plants and grains in high Cd soils.Results and discussion: All of the soil samples had a total Cd content exceeding the maximum permissible concentration (0.3 mg kg 1) for soils with the exchangeable fraction taking up 50, 56, and 39%, respectively. For the rice grains harvested from the soils derived from sandshale, limestone, and Quaternary red earth, 67, 95, and 28%, respectively, had a Cd content exceeding the maximum permissible concentration for grain (0.2 mg kg 1). The results demonstrated high Cd bioavailability in these areas and indicated potential health risk when people ingest the rice grains. Cd measured by DGT best reflected Cd bioavailability. The Cd in soil solution (Cdsoln), which is directly available, and CaCl2-extracted Cd were also significantly related to grain Cd content. Factor relative importance assessment based on random forest (RF) showed that soil pH was among the top two most important physicochemical factors of the three types of soils influencing Cd accumulation in rice grains. Besides, dissolved organic carbon (DOC), clay, and dithionite-citrate-bicarbonate-extracted Mn (MnDCB) was the other major influencing factor in the sandshale soils, limestone soils, and Quaternary red earths, respectively.Conclusions: The results indicated that DGT technique better predicted Cd bioavailability. Manipulating soil pH could be used to reduce Cd bioavailability and its accumulation in plants. However, manipulating soil DOC, clay and Fe/Mn content were soil-type-dependent.

23438. 题目: Early structural stability of fine dam sediment in soil construction
文章编号: N18070104
期刊: Journal of Soils and Sediments
作者: Gaetan Fourvel, Laure Vidal-Beaudet,Agathe Le Bocq,Violaine Brochier,Fran?ois Théry, David Landry, Thagshayini Kumarasamy,Patrice Cannavo
更新时间: 2018-07-01
摘要: Purpose: Fine sediments accumulate upstream of hydroelectric dams. To ensure that dams can operate properly, most sediments are returned downstream reaches, but a portion of them have to be dredged and land managed. In parallel, using topsoil from agricultural parcels for urban greening is currently controversial because arable surface areas are decreasing. An alternative idea for protecting these natural resources consists in reusing fine dredged sediment to construct functional soils. The agronomical use of fine dredged sediment raises the question of its ability to provide acceptable physical properties for plant growth. Materials and methods: Six dredged sediments with contrasted initial agronomical properties were mixed or not with green waste compost and submitted or not to drying-wetting cycles in a 105-day-long experiment under greenhouse conditions. The sediments were analyzed for their capacity to generate stable aggregates. We measured the proportion of macro aggregates > 2 mm with dry-sieved aggregate (DSA) fraction and the > 0.25 mm water-stable aggregate (WSA) fraction for each treatment over time. We also assessed the main sediment physicochemical properties, microbial biomass carbon, and carbon mineralization potential. Results and discussion: Compost addition (40% in volume) enhanced the WSA fraction of the low-organic-matter-content sediments (< 30 g kg 1), whereas it had a non-significant effect in the other sediments. Multiple linear regressions highlighted a determining role of organic matter in the WSA fraction. At this scale of aggregation, organic matter seemed to mainly interact with clay in an acidic context. Compost addition had either no significant effect or a negative effect on the DSA fraction. Multiple linear regressions suggested that organic matter was not clearly involved in DSA formation in the sediment, whereas macro-porosity was. The first drying-wetting cycles enhanced the DSA proportion of the sediments, but the following cycles had a negative effect. We suggest that disaggregating mechanisms gradually predominated over aggregating mechanisms over time. Conclusions: All sediments showed acceptable physicochemical properties for plant growth. WSA formation in low-organic-matter-content sediments was improved by adding compost. Drying-wetting cycles had a controversial effect on DSA formation, and only the very first cycles had a beneficial effect on macro-aggregation. The mechanisms involved in aggregation and aggregate stability in soil constructed from sediments seem to be similar to those involved in natural soils. That is why we propose that the soil hierarchical aggregation model initially developed for natural and cultivated soils could be adapted to sediments.

23439. 题目: Pentachlorophenol dissipation and ferrous iron accumulation in flooded paddy soils with contrasting organic matter contents and incorporation of legume green manures
文章编号: N18070103
期刊: Journal of Soils and Sediments
作者: Yong Liu, Sifan Wang, Lian Zhu, Yunsheng Xia, Huihua Zhang, Shan Wang,Xiongsheng Yu, Jun Lou, Fangbai Li, Jianming Xu
更新时间: 2018-07-01
摘要: Purpose: The effects of different amendment rates (1 and 3%) of Chinese milk vetch (Astragalus sinicus L.) and bird vetch (Vicia cracca L.) on the dissipation of extractable pentachlorophenol (PCP) residues were investigated in two flooded paddy soils with contrasting soil organic matter (SOM) contents. Following incorporation of the legume green manures, whether acetate-extractable ferrous iron [Fe(II)NaOAc] is useful for revealing the reductive dechlorination mechanism of PCP in flooded paddy soils was verified. Materials and methods: The kinetic parameters of PCP dissipation and Fe(II)NaOAc accumulation were estimated using logistic curve fitting. Correlation and regression analyses were performed on PCP, Fe(II)NaOAc, water-soluble organic carbon (WSOC), pH, and oxidation-reduction potential data. Results and discussion: The kinetic parameters of PCP dissipation and Fe(II)NaOAc accumulation varied significantly with the amendment rate of legume green manure. The changes in pH value and WSOC content varied significantly with the level of SOM and with the amendment rate of legume green manure. At a low amendment rate of green manure, the pH increase and WSOC consumption greatly enhanced Fe(II)NaOAc accumulation and contributed to PCP dissipation. The rate of PCP dissipation decreased with decreasing pH and WSOC accumulation, especially in the high-SOM soil amended with the higher rate of green manure. Legume green manure species had no effect on PCP dissipation. Conclusions: In terms of soil chemistry, Fe(II)NaOAc was found to be the key variable that could explain the mechanisms involved in the reductive dissipation of PCP in flooded paddy soils with contrasting SOM contents and incorporation of legume green manures.

23440. 题目: Retention of silver nanoparticles and silver ion to natural soils: effects of soil physicochemical properties
文章编号: N18070102
期刊: Journal of Soils and Sediments
作者: Rui Wang, Huan Du, Yujun Wang, Dengjun Wang, Qian Sun, Dongmei Zhou
更新时间: 2018-07-01
摘要: Purpose: The mass production and widespread use of silver nanoparticles (AgNPs) have led to their wide dissimilation in the subsurface environments (e.g., natural soils). The retention propensities of AgNPs in soils dictate their fate, transport, and transformation in the subsurface environments. The aim of this study was to explore the retention behaviors of AgNPs and Ag+ ion (as a comparison) in ten natural soils with different physicochemical properties, identifying which properties dominate their mobility in soils. Materials and methods: Ten surface (0–20 cm) soils sampled across five geographical regions of China and AgNPs coated by polyvinylpyrrolidone (PVP) with an average transmission electron microscopy (TEM) diameter of ~ 10 nm were used in this study. Batch retention experiments of AgNPs and AgNO3 in ten soils (pass through 60-mesh sieve) were conducted in triplicate at 25 °C for 24 h. Multiple regression analyses of maximum retention capacity (Qmax for AgNPs or Ag+ ion) simulated by Langmuir retention models were performed to identify which soil physicochemical properties dominate the retention behavior of AgNPs and Ag+ ion. TEM combined with energy dispersive X-ray spectroscopy (EDS) analyses was applied to visually unravel the distribution and retention behavior of AgNPs on natural soils. Results and discussion: The results of batch retention experiments showed that Langmuir model well-approximated the retention isotherms of AgNPs and Ag+ on ten soils and that the Qmax value of AgNPs was generally lower than that of Ag+ on soils. The results of multiple regression analyses showed that the retention capacity of AgNPs on soils was positively correlated with the iron oxide content, which is visually confirmed by TEM-EDS observations, whereas retention capacity of Ag+ ions was mainly related to soil organic matter (SOM) content. Conclusions: Maximum retention capacity of AgNPs and Ag+ ion in soils varied with soil physicochemical properties, and particularly, iron oxide and SOM contents are two pivotal parameters controlling Qmax. These findings advance our current understanding of the mechanisms controlling retention and transport of AgNPs in natural soils, which represents an important step toward predicting the fate, transport, and potential toxicity of AgNPs in the subsurface environment.

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