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28041. 题目: Evaluating ultraviolet (UV) based photochemistry in optically complex coastal waters using the Hyperspectral Imager for the Coastal Ocean (HICO)
文章编号: N18102408
期刊: Estuarine, Coastal and Shelf Science
作者: Fang Cao, Deepak R. Mishra, John F. Schalles, William L. Miller
更新时间: 2018-10-24
摘要: Knowledge of light partitioning into different optically active constituents, particularly chromophoric dissolved organic matter (CDOM) in the ultraviolet (UV) is indispensable for understanding UV dependent biogeochemical issues including photochemical processes in optically complex waters. Herein a new approach is presented to investigate photochemistry by blending two ocean color algorithms, namely the composite SeaUV (Cao et al., 2014) and the SeaCDOM (Cao and Miller, 2014) algorithms, and applying them to visible remote sensing reflectance (Rrs) measured using the Hyperspectral Imager for the Coastal Ocean (HICO). As illustrated using photochemical carbon monoxide (CO) production from CDOM, this model approach allows high resolution examination of UV optical details with estimates of both depth-specific and depth-integrated photoproduction rates in a dynamic estuarine/coastal environment. Decoupled retrievals of inherent and apparent optical properties (i.e. diffuse attenuation coefficient (Kd) and CDOM absorption coefficient (ag)) using two distinct ocean color algorithms over the entire UV spectrum allow a synoptically dynamic view of CDOM's contribution to light attenuation (ag/Kd). This provides new potential to probe UV processes in complex coastal waters on regional as well as global scales using remote sensing of ocean color.
28042. 题目: Soil micro-food web interactions and rhizosphere priming effect
文章编号: N18102407
期刊: Plant and Soil
作者: Xinchang Kou, Tongqing Su, Ningning Ma, Qi Li, Peng Wang, Zhengfang Wu, Wenju Liang, Weixin Cheng
更新时间: 2018-10-24
摘要: Background and aims: The rhizosphere priming effect (RPE) is the stimulation or suppression of soil organic matter decomposition by living roots and associated rhizosphere organisms. The RPE is pivotal in regulating biogeochemical cycles in terrestrial ecosystems. However, biological mechanisms, especially soil micro-food web interactions, behind the RPE remain largely unknown. Methods: We quantified the RPE of soybean and cottonwood at three growth stages using a natural 13C tracer method, measured soil microbial and nematode community composition, and investigated their relations with the RPE. Results: The magnitude of the RPE varied widely at different growth stages. Soybean produced a greater cumulative RPE than cottonwood. The plant species effect was also observed in the bacterial PLFA with higher values found in the soybean treatment. Mantel test analysis suggested that the variations in microbial community were closely related with the RPE, soil and plant characteristics. The nematode community affected the RPE indirectly through altering the structure of the microbial community. Conclusions: We demonstrated that the RPE was connected with interactions of soil micro-food webs. This connection indicates that soil micro-food web interactions in the rhizosphere may either regulate microbial turnover and/or microbial community composition, subsequently modulating the RPE.
28043. 题目: Shooting range contamination: mobility and transport of lead (Pb), copper (Cu) and antimony (Sb) in contaminated peatland
文章编号: N18102406
期刊: Journal of Soils and Sediments
作者: Gudny Okkenhaug, Andreas Botnen Smebye, Thomas Pabst, Carl Einar Amundsen, Hilmar Sævarsson, Gijs D. Breedveld
更新时间: 2018-10-24
摘要: Purpose: Small arm shooting ranges located in peatland areas are gathering increased attention due to severe metal and antimony (Sb) contamination and challenging conditions for remediation. The goal of the present study was to gain further understanding of the distribution, binding and transport of lead (Pb), copper (Cu) and Sb in peatland contaminated by small arm shooting range activities. Materials and methods: A field experiment was carried out at a recently closed shooting range facility in Norway, including (i) peat soil sampling for various selective extractions (water, chemical extractions, extractions by diffusive gradients in thin films, DGT), (ii) establishing groundwater wells for groundwater sampling and monitoring of groundwater level and (iii) sampling of water and sediments in surface water. The results from groundwater monitoring were used to carry out hydrogeological numerical simulations using Seep/W and CTran/W. These models were used to evaluate the residence time of the contaminants in the peatland. Results and discussion: Increased metal concentrations were observed in the top layer of the peatland, indicating low vertical transport. Groundwater revealed high concentrations of Pb (22 ± 5 μg/L), Cu (16 ± 6 μg/L) and Sb (11 ± 2 μg/L), the dominating contaminant source to the downstream surface water. Hydrogeological modelling indicated that transport mainly happened in the upper peat layer, as a result of a higher hydraulic conductivity close to the surface and a high groundwater table. Pb (6.9 ± 0.1 μg/L), Cu (24.0 ± 0.0 μg/L) and Sb (7.4 ± 0.1 μg/L) concentrations in the stream samples confirmed the spreading of contaminants at levels toxic to aquatic organisms. Pb and Cu were most likely associated with dissolved organic carbon (DOC), whereas Sb showed no correlation with DOC. Conclusions: The elements contaminating the peatland may leak to the nearby water course over a long-term period. Copper showed the highest concentration in the stream water despite considerably higher levels of Pb in the peat soil. Strong complexation of Cu to dissolved organic matter might explain this observation. Only a little fraction of the contaminants is transported in a particulate form, and therefore are increased sedimentation measures not considered as viable remediation option.
28044. 题目: Positive effects of apple branch biochar on wheat yield only appear at a low application rate, regardless of nitrogen and water conditions
文章编号: N18102405
期刊: Journal of Soils and Sediments
作者: Shuailin Li, Zhouping Shangguan
更新时间: 2018-10-24
摘要: Purpose: The agriculture industry is under intense pressure to produce more food with a lower environmental impact, while also mitigating climate change. Biochar has the potential to improve food security while improving soil fertility and sequestering carbon. The aim of our research was to evaluate the effects of apple branch biochar on wheat yield and soil nutrients under different nitrogen (N) and water conditions. Materials and methods: Durum wheat was grown for nearly 6 months in pots with silt clay soil supplemented with apple branch biochar. The biochar was applied at five rates (0, 1, 2, 4, and 6% w/w; B0, B1, B2, B3, and B4), and N fertilizer was applied at three rates (0, 0.2, and 0.4 g kg−1; N0, N1, and N2). From the jointing to maturation stages, the soil water content was controlled at two rates to simulate sufficient water and drought conditions (75 and 45% of field capacity; W1 and W2). After harvest, we investigated grain yield and soil nutrient status. Results and discussion: The application of biochar alone had a positive effect on wheat production and soil nutrients, especially under sufficient water conditions. Compared with the addition of N fertilizer alone, the addition of biochar at B1 and B2 combined with N fertilizer under sufficient water conditions increased the crop yield by 7.40 to 12.00%, whereas this was not the case under drought stress. Furthermore, regardless of water conditions, compared with N fertilizer application alone, a high rate of biochar application (B3 and B4) led to a significant decrease in the grain yield of approximately 6.25–21.83%. Biochar had strong effects on soil nutrients, with NO3− and available phosphorus contents and the C:N ratio exerting the greatest effects on wheat yield. Conclusions: The effects of biochar on wheat production and soil nutrients varied with the biochar application rate, N fertilizer application rate, and water conditions. Drought stress weakened or offset the positive effect of biochar on crop production, especially under the high-N level (N2) conditions. The optimum application combination was 1% (or possibly even less) apple branch biochar (B1) and moderate N fertilizer (N1).
28045. 题目: Land-use change affects stocks and stoichiometric ratios of soil carbon, nitrogen, and phosphorus in a typical agro-pastoral region of northwest China
文章编号: N18102404
期刊: Journal of Soils and Sediments
作者: Xiang Liu, Lanhai Li, Quan Wang, Shuyong Mu
更新时间: 2018-10-24
摘要: Purpose: The impacts of land-use change on dynamics of soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) in the subsoil (> 30 cm) are poorly understood. This study aims to investigate whether the effects of land-use change on stocks and stoichiometric ratios (RCN, RCP, and RNP) of SOC, TN, and TP can be different between topsoil (0–30 cm) and subsoil (30–60 cm) in the Ili River Valley, northwest China. Materials and methods: Soil samples (0–10, 10–20, 20–30, 30–40, 40–50, and 50–60 cm) were collected from a pasture (PT), a 27-year-old cropland (CL) converted from PT, and a 13-year-old poplar (Populus tomentosa Carr.) plantation (PP) converted from CL. SOC, TN, and TP concentrations and soil bulk density were determined to calculate stocks and stoichiometric ratios (molar ratios) of SOC, TN, and TP. Results and discussion: Conversion from PT to CL led to substantial losses in SOC, TN, and TP pools in both topsoil and subsoil, and the reduction rates in subsoil (13.8–24.7%) were higher than those in topsoil (8.5–17.3%), indicating that C, N, and P pools in subsoil could also be depleted by cultivation. Similar to topsoil, significant increases in SOC, TN, and TP stocks were detected after afforestation on CL in subsoil, although the increase rates (31.2–56.2%) were lower than those in topsoil (47.8–69.1%). Soil pH and electrical conductivity (EC), which generally increased after conversion from PT to CL while decreased after CL afforestation, showed significant negative correlations with SOC, TN, and TP, suggesting that cultivation might lead to soil degradation, whereas afforestation contributed to soil restoration in this area. Significant changes in C:N:P ratios in topsoil were only detected for RNP after conversion from CL to PP. By contrast, land-use change significantly altered both RCN and RNP in the subsoil, demonstrating that the impacts of land-use change on RCN and RNP were different between topsoil and subsoil. The significant relationship between soil EC and RNP suggested that RNP might be a useful indicator of soil salinization. Conclusions: Stocks of SOC, TN, and TP as well as RCN and RNP in subsoil showed different responses to land-use change compared to those in topsoil in this typical agro-pastoral region. Therefore, it is suggested that the effects of land-use change on dynamics of SOC, TN, and TP in subsoil should also be evaluated to better understand the role of land-use change in global biogeochemical cycles.
28046. 题目: Effect of biochar amendment on water infiltration in a coastal saline soil
文章编号: N18102403
期刊: Journal of Soils and Sediments
作者: Junna Sun, Runya Yang, Wenxue Li, Yinghua Pan, Mengzhu Zheng, Zhenhua Zhang
更新时间: 2018-10-24
摘要: Purpose: Increasing data have shown that biochar amendment can improve soil fertility and crop production, but there is little knowledge about whether biochar amendment can improve water infiltration in saline soils. We hypothesized that biochar amendment could promote water infiltration in saline soil. The aims of this study were to evaluate the effects of biochar amendment on water infiltration and find the suitable amendment rate and particle size of biochar as a saline soil conditioner. Materials and methods: We measured water infiltration parameters in a coastal saline soil (silty loam) amended with non-sieved biochar at different rates (0.5, 1, 2, 5, and 10%, w/w) or sieved biochar of different particle sizes (≤ 0.25 mm, 0.25–1 mm, and 1–2 mm) at 1 and 10% (w/w). Results and discussion: Compared with the control, amending non-sieved biochar at 10% significantly decreased water infiltration into the saline soil (P < 0.05). In contrast, sieved biochar of ≤ 0.25 mm significantly improved water infiltration capacity, irrespective of the amendment rate. Sieved biochar of 1–2 mm was less effective to improve soil porosity and when amended at 10%, it even reduced the water infiltration capacity. The Philip model (R2 = 0.983–0.999) had a better goodness-of-fit than the Green-Ampt model (R2 = 0.506–0.923) for simulation of cumulative infiltration. Conclusions: Amending biochar sieved to a small particle size improved water infiltration capacity of the coastal saline soil compared with non-sieved biochar irrespective of the amendment rate. This study contributes toward improving the hydrological property of coastal saline soil and rationally applying biochar in the field.
28047. 题目: Combined effects of cropping types and simulated extreme precipitation on the community composition and diversity of soil macrofauna in the eastern Qinghai-Tibet Plateau
文章编号: N18102402
期刊: Journal of Soils and Sediments
作者: Sizhong Wang, Kaiwen Pan, Akash Tariq, Lin Zhang, Xiaoming Sun, Zilong Li, Feng Sun, Qinli Xiong, Dagang Song, Olusanya Abiodun Olatunji
更新时间: 2018-10-24
摘要: Purpose: Extreme precipitation as global change greatly affects above- and below-ground biodiversity. Soil macrofauna play a key role in the agroforestry ecosystem processes. Extreme precipitation might negatively impact soil macrofauna by changing soil water content. Particularly, whether cropping types are beneficial to alleviate response of soil macrofauna to extreme precipitation remains unexplored. Materials and methods: Effects of simulated extreme precipitation of 1 month on soil macrofauna were studied under Chinese prickly ash (Zanthoxylum bungeanum) intercropped with soybean (Glycine max), Chinese prickly ash intercropped with sweet pepper (Capsicum annuum), and Chinese prickly ash monoculture. Soil macrofauna and soil samples were collected in three soil depths (0–10, 10–20, and 20–30 cm) per plot. The abundance, diversity, and vertical distribution of soil macrofauna were analyzed for each sample at genus and trophic level. Each sieved soil sample was analyzed for soil water content, soil nitrate nitrogen (NO3−–N), ammonium nitrogen (NH4+–N) and organic matter. Descriptive statistics and significance tests on raw data were carried out using the SPSS 16.0 software at P < 0.05. Results and discussion: A total of 502 soil macrofauna individuals were observed, and belonged to 14 genera, and consisted mainly of earthworms, arthropods. The richness, density, and biomass, as well as vertical distribution of total soil macrofauna were unaffected by extreme precipitation. Only Eisenia density and biomass were significantly decreased by extreme precipitation. The plots intercropped with soybean had higher density, biomass, and richness than the plots intercropped with sweet pepper and prickly ash monoculture. Cropping types significantly influenced density of total soil macrofauna under control condition but not extreme precipitation treatment. The abundance of total soil macrofauna was significantly and positively related to soil NH4+–N, total soil inorganic N, and soil organic matter. Conclusions: Our results suggest that the impacts of cropping types rather than extreme precipitation on soil macrofauna abundance, diversity, and vertical distribution are significant. However, extreme precipitation changes the response of soil macrofauna to cropping types.
28048. 题目: Characteristics of hydrophobic and hydrophilic acid fractions in drainage waters of undisturbed soil lysimeters
文章编号: N18102401
期刊: Journal of Soils and Sediments
作者: Guixue Song, Etelvino H. Novotny, Karl G. Richards, Michael H. B. Hayes
更新时间: 2018-10-24
摘要: Purpose: Dissolved organic matter (DOM), a heterogeneous mixture of low concentrations of organic matter draining from soils, plays a significant role in soil C cycling and in nutrient and pollutant transport. DOM from undisturbed soil profiles has rarely been studied. Hydrophobic acids (Ho) and hydrophilic acids (Hi), the major components of DOM, were recovered, using XAD-8 and XAD-4 resins in series, from waters draining in winter and in spring periods from well-drained and poorly drained Irish grassland soil profiles in lysimeters. Materials and methods: Waters were collected from 45 soil undisturbed lysimeters at the Teagasc Research Centre, Johnstown Castle, Wexford, Ireland. Four Irish representative soils had been collected as undisturbed 1.0-m-deep monoliths, transported to the experiment site and arranged randomly in an experimental facility. Water collections were carried out in winter and spring periods. The DOM was isolated and fractionated using an XAD-8 and XAD-4 resins in-tandem procedure, and hydrophobic acids (Ho) and hydrophilic acids (Hi) were isolated. Results and discussion: The amounts of DOM recovered in the winter period were much greater than those in the spring period, and the soil types had only minor influences on the DOM concentrations recovered. The Ho and Hi fraction contents ranged from 62 to 90 and 10 to 28%, respectively, of the total DOM content extracted. The Hi acids were most enriched in 13C, and considered to reflect greater microbial inputs. The neutral sugar (NS) contents for the Ho and Hi fractions were in the range of 15 to 52 μg mg−1, with the Hi fraction most enriched. The amino acids (AAs) for the Ho and Hi fractions varied from 0.6 to 2.4%, and the total AAs and NS of the Ho acids were well correlated. The DOM fractions from the drainage waters contained much less AAs and NS than the corresponding fractions in the parent soils. The solid- and liquid-state NMR data indicated organic structures with low aromaticity, significant amounts of carbohydrate and with lesser amounts of peptide structures, and with long-chain methylene (CH2)n and methine (-CH-) groups. Conclusions: The application of a variety of wet chemistry and of spectroscopy procedures has given a more in-depth awareness of the compositions of the DOM in the drainage waters from four different soils in 1.0-m-deep lysimeter arrangements. Based on wet chemistry analyses, and FTIR and liquid- and solid-state NMR spectrometry, it is clear that there are some differences between the compositions of the DOM fractions recovered. Alkyl functionalities dominated the structures. These included significant amounts or O-alkyl (predominantly carbohydrate), and with lesser (and variable amounts in the different fractions) aromatic structures (to which aromatic amino acid components were considered to be significant contributors), and with no evidence for lignin-derived structures The results suggest that, during residence in the soil solution, microbiological processes transform the SOM components released into products that are greatly different from their materials of origin in the SOM.
28049. 题目: Toxicity of silver nanoparticles to green algae M. aeruginosa and alleviation by organic matter
文章编号: N18102307
期刊: Environmental Monitoring and Assessment
作者: Li Xiang, Juan Fang, Hua Cheng
更新时间: 2018-10-23
摘要: Silver nanoparticles (AgNPs) have been increasingly used in a wide range of consumer products over the last decade. The release of AgNPs into aquatic ecosystems raises concerns about their safety and environmental toxicity, which have been the subject of recent studies. Herein, we assess the toxicity of AgNPs to the common algae Microcystis. aeruginosa. A toxicological response by M. aeruginosa was exhibited at an early stage of exposure to AgNPs, which were also toxic to its growth, photosynthetic, and membrane systems. The attachment of AgNPs to microalgae is likely the main mechanism by which it damages cell membranes. Dissolved Ag ions, originating from internalized AgNPs, seem to directly target the photosynthetic system. We also found that several humus-related indicators of water quality (HIX and β/α) were related to reduced AgNPs toxicity.
28050. 题目: Extreme 13C-depletions and organic sulfur content argue for S-fueled anaerobic methane oxidation in 2.72 Ga old stromatolites
文章编号: N18102306
期刊: Geochimica et Cosmochimica Acta
作者: Kevin Lepot, Kenneth H. Williford, Pascal Philippot, Christophe Thomazo, Takayuki Ushikubo, Kouki Kitajima, Smaïl Mostefaoui, John W. Valley
更新时间: 2018-10-23
摘要: The extreme 13C-depletions recorded in Neoarchean organic matter (OM) have commonly been interpreted as markers of methanotrophy. This methane oxidation metabolism could have been performed using oxidants such as dioxygen, sulfate, nitrite/nitrate, and/or Fe3+- and Mn4+-minerals. Acetogenesis using acetyl-CoA metabolism may produce similar 13C-depletions. We investigated δ13C and S/C values of OM in 2.72 Ga old lacustrine stromatolites of the Tumbiana Formation (Australia) using Secondary Ion Mass Spectrometry (SIMS), coupled with X-ray spectroscopy. Type-A OM is embedded in quartz and/or chlorite. We show that mixtures of chlorite bias negatively the δ13Corg of associated OM measured by SIMS, likely through recombination of hydrogen from chlorite with carbon from OM during analysis. Type-A OM, associated with quartz or interleaved with chlorites (but remote enough to avoid H-recombination), displays δ13Corg between –56.1 and –50.6 ‰ VPDB (mean: –53.5 ‰, SD ±1.8 ‰). The intimate association of Type-A OM with Fe-rich chlorite and its main occurrence in pyritic layers coupled with 13C-depletions is most parsimoniously interpreted as anaerobic methanotrophy using Fe3+-minerals and/or oxidized S. Type-B OM comprises <2-µm organic globules embedded in calcite. A mass balance correction using the δ13C values measured on Type-B globules mixed with calcite and those measured on pure calcite yielded corrected δ13C∗org values for the globules ranging between –65.2 and –52.5 ‰ (mean –58.8 ‰, SD ±3.6 ‰). In a context where Fe and S reduction could outcompete acetogenesis for a fraction of any available H2, these extremely low δ13Corg values are difficult to explain with chemoautotrophic acetogenesis. Atomic S/C ratios in Type-B globules reach up to 0.042, i.e. up to tenfold the values (0.003–0.004) in Type A-OM. These organic S concentrations, combined with the extremely low δ13C∗org values, support anaerobic oxidation of methane coupled to sulfur oxidation. Finally, Type-C OM, interpreted as migrated pyrobitumen nodules, displays δ13Corg of –48 to –39.1 ‰. The most extreme low-δ13Corg values of the Precambrian are thus best interpreted as the result of lacustrine methanotrophy fueled by oxidized S and/or Fe species, which likely derived from oxygenic and/or anoxygenic photosynthesis. Photosynthesis, followed by methanogenesis and methanotrophy may have been important in lakes at a time of supercontinent growth and eruption of large subaerial igneous provinces. In this context, anaerobic methanotrophy could have played a part in regulating atmospheric methane.
28051. 题目: Enhancement of coal waste slurry flocculation by CTAB combined with bioflocculant produced by Azotobacter chroococcum
文章编号: N18102305
期刊: Separation and Purification Technology
作者: Zhichao Yang, Shengyu Liu, Wenbing Zhang, Quanbao Wen, Yongjie Guo
更新时间: 2018-10-23
摘要: A bioflocculant produced by Azotobacter chroococcum, a natural polymer containing sugar and protein, can be used to flocculate coal waste slurry, but electrostatic repulsion impacts the flocculation of quartz attached to the solid coal particles. In this work, cetyltrimethylammonium bromide (CTAB) combined with this bioflocculant were used to flocculate coal waste slurry. The adsorption and zeta potential of CTAB on quartz, kaolinite, and organic matter were investigated in aqueous media. The results show that the data for CTAB adsorption fit the typical Langmuir adsorption model, and that the CTAB adsorption level is higher in an alkaline medium than in an acidic medium. The electrostatic interaction and formation of π-complexes contributed to the adsorption of CTAB on minerals and organic matter. Zeta potential measurements demonstrated that the point of zero charge values shifted to higher pH values after CTAB adsorption on mineral and organic matter surfaces. Furthermore, the behavior of the bioflocculant with the addition of CTAB was investigated to determine the effect of CTAB on the flocculation of coal waste slurry; quartz, kaolinite, and organic matter were used for comparison. Flocculation tests indicated that the optimum CTAB dosage for obtaining higher flocculation rates and clearer suspension of organic matter, quartz, and kaolinite was 50, 100, and 40 mg/L, respectively. A higher flocculation rate and clearer suspension of quartz were obtained in a very acidic medium, while organic matter suspension continued to increase in the pH range of 2.2–6.2 and remained almost constant in an alkaline medium. In addition, there were no significant changes in the flocculation rate or turbidity of kaolinite with an increase in pH. CTAB exhibited significant enhancement in terms of flocculation of coal waste slurry when the bioflocculant was used as a flocculant. Finally, surface tension measurements were taken to confirm the interaction between the bioflocculant and CTAB. The results show that CTAB could bind to the bioflocculant and form complexes.
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28052. 题目: Selective removal of dissolved organic matter affects the production and speciation of disinfection byproducts
文章编号: N18102304
期刊: Science of The Total Environment
作者: Clayton J. Williams, Dan Conrad, Dolly N. Kothawala, Helen M. Baulch
更新时间: 2018-10-23
摘要: The heterogeneity of dissolved organic matter (DOM) in natural and human impacted waters and the variety of drinking water treatment processes employed has made a mechanistic understanding of disinfection byproduct (DBP) formation challenging. In this study, we examined the formation of the regulated DBPs (Trichloromethanes, THM, and Haloacetic acids, HAA) during full-scale water treatment operations both with prechlorination treatment (normal operations for the drinking water plant) and without (altered operations); followed by coagulation, flocculation, filtration, and chlorination. The source water DOM concentration ranged 6.4 to 7.3 mg-C/L. DOM composition was moderately humic and degraded with a mix of microbial- and terrestrial-like characteristics. Removal of raw water prechlorination caused an average reduction in total THM and HAA concentrations of 52.7% and 40.0%, respectively, with the greater reduction noted for chlorinated-DBPs rather than brominated-DBPs. Prechlorination treatment resulted in a higher relative production of Cl3CH and BrCl2CH associated with aromatic, humic, and terrestrial-like DOM. Without prechlorination, the DBP pool had higher proportions of brominated-DBPs (Br3CH, Br2ClCH, Br2CHCOOH, BrClCHCOOH, and BrCH2COOH) associated with microbial-like, processed humic-like, and protein-like DOM. These observed patterns could not be explained by chloride demand and DOM concentration, indicating that DOM composition played an important role in DBP formation.
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28053. 题目: Real cover crops contribution to soil organic carbon sequestration in sloping vineyard
文章编号: N18102303
期刊: Science of The Total Environment
作者: Agata Novara, Mario Minacapilli, Antonino Santoro, Jesus Rodrigo-Comino, Alessandra Carrubba, Mauro Sarno, Giacomo Venezia, Luciano Gristina
更新时间: 2018-10-23
摘要: The research focused on the evaluation of the effect of soil erosion processes on SOC sequestration rate after 5 years of cover crop soil management in Mediterranean vineyards (Sicily, Italy). Two paired sites, one in a sloping area and another one in a contiguous flat area, were chosen. The vineyard soils of the two plots of each paired site were managed with conventional soil tillage (CT) and Vicia faba cover crop (CC) the preceding 5 years. SOC was measured in three points along the slope (top, middle and foot parts) and in the flat area. Results showed that in the slope area the highest SOC content was found in CC management, with an average value of 9.52 ± 0.34 g kg−1, whereas the SOC content under CT was 8.74 ± 0.20 g kg−1. In the flat vineyard, the SOC ranged from 9.88 ± 0.11 g kg−1 to 10.47 ± 0.20 g kg−1 under CT and CC, respectively.The SOC increase was 6% in the flat area and 9% in the sloping vineyard after five years since CC management adoption. The higher C sequestration rates in the sloping vineyard in comparison to the flat area could be attributed to the role of CC to prevent sediment and nutrient erosion. These results were compared with those by reference works and with the results of 39 vineyards paired-sites. Findings demonstrated that C sequestration rate is strongly correlated to slope gradient and the C sequestration per se due to the effect of added C input by the cover crop is overestimated.
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28054. 题目: Photo-transformation of atrazine in aqueous solution in the presence of Fe3+-montmorillonite clay and humic substances
文章编号: N18102302
期刊: Science of The Total Environment
作者: Ran Hong, Lin Zhang, Wei Zhu, Cheng Gu
更新时间: 2018-10-23
摘要: As one of the most troublesome herbicides, the natural behavior of atrazine has drawn great attentions. Currently, most studies investigated the adsorption of atrazine on clay minerals and humic substances (HSs), whereas, the transformation of atrazine catalyzed by clay and HSs was still unknown. In the present study, photo-degradation of atrazine in the presence of Fe3+-montmorillonite and Suwannee river fulvic acid (SRFA) in aqueous solution was systematically studied. In the Fe3+-montmorillonite system, the hydroxyl radical (OH) induced removal of atrazine was strongly pH-dependent and the reaction rate increased with the decrease of pH. The presence of SRFA suppressed the atrazine degradation by Fe3+-montmorillonite at pH 3 but promoted its removal rate in the pH range of 4–6. Our results demonstrated that both OH and singlet oxygen are responsible for the degradation process in the Fe3+-montmorillonite/SRFA hybrid system. The degradation of atrazine followed the cleavage of the CN bonds in aliphatic chains of atrazine, and three major products, desethylatrazine, desisopropylatrazine and desethyldesisopropylatrazine were detected. The toxicity assessment showed that the toxicity of the reaction solution significantly decreased after the radical reactions, indicating that the transformation of atrazine on natural clay minerals with/without HSs could be considered as a detoxification pathway, which might be important to evaluate the environmental risk of atrazine in a natural system.
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28055. 题目: Carbon and nitrogen inputs differentially affect priming of soil organic matter in tropical lowland and montane soils
文章编号: N18102301
期刊: Soil Biology and Biochemistry
作者: Lettice C. Hicks, Patrick Meir, Andrew T. Nottingham, Dave S. Reay, Andrew W. Stott, Norma Salinas, Jeanette Whitaker
更新时间: 2018-10-23
摘要: Microbial decomposition of soil organic matter (SOM) can be accelerated or reduced by the combined effects of carbon (C) and nutrient inputs through a phenomenon known as ‘priming’. Tropical lowland and montane soils contain large stores of C and may undergo substantial future changes in C and nutrient inputs due to global change, yet how these inputs might interact to influence priming is poorly understood in these ecosystems. We addressed this question using soils from a 3400 m tropical elevation gradient which vary strongly in nitrogen (N) and phosphorus (P) availability. To determine how existing nutrient availability in different tropical soils regulates microbial activity, and whether microbial demand for nutrients leads to priming, soils were amended with simple and more complex 13C-labelled substrates in combination with inorganic N, P and N + P. Isotopic partitioning (13C in CO2 and in phospholipid fatty acids; PLFA) was used to identify sources of C (substrate- or SOM-derived) in respiration and in microbial communities. Nutrient treatments did not influence the amount of substrate-respired C for any of the soils, but did affect the direction and magnitude of priming effects. For the upper montane forest and grassland soils, C addition had a relatively minor influence on the turnover of SOM, but N addition (with or without C) reduced SOM mineralisation (negative priming), suggesting reduced microbial N-mining from SOM when N was externally supplied. By contrast, in the lower montane and lowland forest soils, C addition increased SOM mineralisation (positive priming), but the response was unaffected by nutrient additions. The assimilation of 13C substrates into functionally active microorganisms revealed that C substrate complexity, but not added nutrients, strongly affected C-use within the microbial community: in both lowland and montane forest soils, fungi assimilated a greater proportion of the simple C substrate, while gram-positive bacteria assimilated a greater proportion of the more complex C substrate. Overall, our results have contrasting implications for the response of soil C cycling in montane and lowland tropical ecosystems under future global change.
28056. 题目: Photo-biochemical transformation of dissolved organic matter on the surface of the coastal East Antarctic ice sheet
文章编号: N18102216
期刊: Biogeochemistry
作者: Runa Antony, Amanda S. Willoughby, Amanda M. Grannas, Victoria Catanzano, Rachel L. Sleighter, Meloth Thamban, Patrick G. Hatcher
更新时间: 2018-10-22
摘要: Recent studies have highlighted the composition and complexity of dissolved organic matter (DOM) in glacial environments. Climate-induced changes to glacier runoff are projected to be an important source of DOM to coastal ecosystems. Photochemical and microbial (termed photo-biochemical) degradation of DOM would determine its fate on the glacier surface and in recipient coastal ecosystems. In order to understand the molecular imprints of photo-biochemical alteration of DOM, in situ field experiments were conducted over a period of 35 days in a coastal Antarctic site and DOM molecularly characterised using ultrahigh-resolution mass spectrometry. We show that the biogeochemistry of DOM is highly complex and intimately connected with microbial and photochemical processes operating individually or in combination. Photo-biochemical processes resulted in shifts in the nitrogen, sulfur, and phosphorous content of the DOM. These processes are also an important mechanism for transforming refractory DOM, like dissolved black carbon and carboxylic rich alicyclic molecules from the snow surface. This study is unique, as it provides new molecular-level information on compounds that comprise the photo- and bio-labile, photo- and bio-refractory, as well as photo- and bio-produced fractions of the supraglacial DOM pool. These insights into the interactions between microbes, light, and specific components of the DOM pool highlight the need for studies focused on the biogeochemistry of supraglacial carbon and its response to a changing climate.
28057. 题目: Distinct responses of ammonia-oxidizing bacteria and archaea to green manure combined with reduced chemical fertilizer in a paddy soil
文章编号: N18102215
期刊: Journal of Soils and Sediments
作者: Yu Fang, Fei Wang, Xianbo Jia, Jichen Chen
更新时间: 2018-10-22
摘要: Purpose: Ammonia oxidation is the rate-limiting step in nitrification. Ammonia-oxidizing bacteria (AOB) and archaea (AOA) are the key drivers of the nitrogen cycle. Chinese milk vetch (MV) has the potential to substitute for part of chemical fertilizer, but it remains unclear how MV is able to replace N fertilizer. The purpose of this study was to investigate the rice yield, soil properties, potential nitrification activity (PNA), abundances, and community structures of ammonia oxidizers in a paddy soil under MV combinations of different rates of chemical fertilizer. Materials and methods: This study was conducted at a long-term Experimental Station of the Fujian Academy of Agricultural Sciences, Fuzhou, China. The treatments included a control (without fertilization), NPK (chemical fertilizer), MF80 (MV plus 80% NPK), MF60 (MV plus 60% NPK), and MF40 (MV plus 40% NPK). Soil samples were collected after the rice harvest. We determined the soil physico-chemical properties and PNA. The abundances and community structures of AOB and AOA were assessed using their ammonia monooxygenase (amoA) genes. Quantitative PCR was used to determine the gene abundance, and Illumina Miseq sequencing was used to explore the diversity of AOB and AOA. Results and discussion: MV significantly increased the soil organic matter and PNA in comparison to the NPK. The available nitrogen content was higher in the MV treatments than in the control and NPK. Compared to the NPK, the application of MV increased the AOB abundance but decreased that of AOA. The abundance of AOA was higher in the control and NPK, but lower in the MV treatments than that of AOB. PNA was significantly positively correlated with the AOB abundance. The primary dominant OTU of the AOB group was Nitrosospira. MV significantly affected the AOB community, while no impact on the AOA community was observed. Principal coordinate analysis showed that the MV treatments were significantly distinct from those of the control and NPK. Redundancy analysis indicated that the soil OM, TN, AN, pH, and PNA were significantly correlated to the AOB community structure. Conclusions: This study demonstrated that MV combined with reduced chemical fertilizer would contribute to the improvement of soil fertility and PNA, resulting in rice yield comparable to that of the NPK. MV had a stronger effect on the AOB community than did chemical fertilizer. AOB played a more important role than AOA in the ammonia oxidation in this soil.
28058. 题目: The Structural Arrangement and Relative Abundance of Aliphatic Units May Effect Long-Wave Absorbance of Natural Organic Matter as Revealed by 1H NMR Spectroscopy
文章编号: N18102214
期刊: Environmental Science & Technology
作者: I. V. Perminova, E.A. Shirshin, A. I. Konstantinov, A. Zherebker, V. A. Lebedev, I. V. Dubinenkov, N. A. Kulikova, E.N. Nikolaev, E. Bulygina, R. M. Holmes
更新时间: 2018-10-22
摘要: The objective of this study was to shed light on structural features which underlay intensity of long wave absorbance of natural organic matter (NOM) using 1H NMR spectroscopy. For this purpose, a set of the NOM samples was assembled from arctic and nonarctic sampling sites (the Kolyma river basin and Moscow region, respectively). It was to ensure a substantial difference in the humification degree of the isolated organic matter—the biogeochemical proxy of the long-wave absorbance of NOM. The assembled NOM set was analyzed using solution-state 1H NMR spectroscopy. The distribution of both backbone and exchangeable protons was determined using acquisition of spectra in three different solvents. The substantially higher contribution of nonfunctionalized aliphatic moieties CHn (e.g., materials derived from linear terpenoids, MDLT) in the arctic NOM samples was revealed as compared to the nonarctic ones. The latter were characterized with the higher content of CHα protons adjacent to electron-withdrawing groups which belong to carboxyl rich alicyclic moieties (CRAMs) or to aromatic constituents of NOM. We have calculated a ratio of CHn to CHα protons as a structural descriptor which showed significant inverse correlation to intensity of long wave absorbance assessed with a use of E4/E6 ratio and the slope of absorption spectrum. The steric hindrance of aromatic chromophoric groups of the NOM ensemble by bulky nonfunctionalized aliphatic moieties (e.g., MDLT) was set as a hypothesis for explanation of this phenomenon. The bulky aliphatics might increase a distance between the interacting groups resulting in inhibition of electronic (e.g., charge-transfer) interactions in the NOM ensemble. The obtained relationships were further explored using Fourier transform mass spectrometry as complementary technique to 1H NMR spectroscopy. The data obtained on correlation of molecular composition of NOM with 1H NMR data and optical properties were very supportive of our hypothesis that capabilities of NOM ensemble of charge transfer interactions can be dependent on structural arrangement and relative abundance of nonabsorbing aliphatic moieties.
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28059. 题目: Temporal controls on dissolved organic carbon biodegradation in subtropical rivers: Initial chemical composition versus stoichiometry
文章编号: N18102213
期刊: Science of The Total Environment
作者: Rong Mao, Siyue Li
更新时间: 2018-10-22
摘要: Dissolved organic carbon (DOC) plays an indispensable role in biogeochemical cycles and ecosystem services in rivers. However, little is known about the seasonal variations of DOC biodegradation in subtropical rivers. Here, we investigated the concentrations of DOC, dissolved total nitrogen (DTN), and dissolved total phosphorus (DTP), humification index (HIX), fluorescence index (FI), and DOC biodegradation in 57 rivers in the dry and wet seasons in the Three Gorges Reservoir area, China, and the aims were to clarify the temporal changes in DOC biodegradation and its driving factors in these subtropical rivers. Compared with dry season, DTN and DTP concentrations, and HIX value were greater, and FI value was lower in the wet season. However, DOC biodegradation remained unchanged across the two sampling seasons. Further, DOC biodegradation negatively correlated with DOC:DTP ratio, DTN:DTP ratio, and FI in the dry season, but only with HIX in the wet season. These findings emphasis that, despite unchanged DOC biodegradation, the key factors driving DOC biodegradation shift from C:N:P stoichiometry in the dry season to initial chemical composition in the wet season in subtropical rivers. Our results regarding the temporal patterns of DOC biodegradation and the underlying mechanisms bear important implications for a better understanding of C dynamics in subtropical river ecosystems.
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28060. 题目: The ratio of Gram-positive to Gram-negative bacterial PLFA markers as an indicator of carbon availability in organic soils
文章编号: N18102212
期刊: Soil Biology and Biochemistry
作者: Nicolas Fanin, Paul Kardol, Mark Farrell, Marie-Charlotte Nilsson, Michael J. Gundale, David A. Wardle
更新时间: 2018-10-22
摘要: Despite recent progress in understanding soil microbial responses to carbon (C) limitation, the functional shifts in microbial community structure associated with decreasing soil C availability and changes in organic matter chemistry remain poorly known. It has been proposed that Gram-negative (GN) bacteria use more plant-derived C sources that are relatively labile, while Gram-positive (GP) bacteria use C sources derived from soil organic matter that are more recalcitrant. Because these two groups may differ in how they influence the fate of different C forms in soils, it is important to understand how they vary across ecosystems that differ in their vegetation cover and ecosystem productivity or across environmental gradients. In this study, we used a 19-year plant functional group removal experiment across a long term post-fire chronosequence to assess how microbial community structure (assessed using phospholipids fatty acids; PLFAs) and the association of bacterial functional groups (specifically, the GP:GN ratio) responded to changes in organic matter chemistry (measured via nuclear magnetic resonance; NMR). We found that the GP:GN ratio increased upon removal of shrubs and tree roots and with decreasing ecosystem productivity along the chronosequence, thus showing the greater dependence of GN than GP bacteria on more labile plant-derived C. Overall, GN bacteria were associated with simple C compounds (alkyls) whereas GP bacteria were more strongly associated with more complex C forms (carbonyls). Therefore, we conclude that the GP:GN ratio has potential as a useful indicator of the relative C availability for soil bacterial communities in organic soils, and can be used as a coarse indicator of energy limitation in natural ecosystems.