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22881. 题目: Biochar and metal-immobilizing Serratia liquefaciens CL-1 synergistically reduced metal accumulation in wheat grains in a metal-contaminated soil Biochar and metal-immobilizing bacteria play an important role in reducing the metal uptake of plants. However, little research has characterized the synergistic effects of biochar and metal-immobilizing bacteria on reducing metal accumulation in wheat grains and the underlying mechanisms. In this study, the effects of biochar, metal-immobilizing Serratia liquefaciens CL-1, and biochar + CL-1 on grain Cd and Pb uptake in wheat (Triticum aestivum L. Sumai-188) and the mechanisms involved under field conditions were characterized. Biochar, CL-1, and biochar + CL-1 reduced wheat grain Cd and Pb contents by 17–25%, 24–27%, and 45–55% and reduced the available Cd and Pb contents in the rhizosphere soils by 14–33%, 13–38%, and 27–57%, respectively, compared with the controls. Biochar, CL-1, and biochar + CL-1 increased soil pH values. CL-1 and biochar + CL-1 increased putrescine contents by 93% and 150% and bacterial aguA gene copy numbers by 30% and 44%, respectively, in the rhizosphere soils compared to the controls based on qPCR analysis. Furthermore, biochar + CL-1 reduced the Cd and Pb bioconcentration and translocation factors by 23–33% compared to the controls. CL-1 significantly increased the pH and reduced water-soluble Cd and Pb concentrations (18–44%) in the metal-contaminated soil solution compared to the controls. The results showed a synergistic effect of biochar and CL-1 on the reduction of Cd and Pb accumulation in wheat grains. These findings suggested that biochar plus CL-1 reduced wheat grain metal uptake by reducing metal availability and translocation from the roots to grains and increasing pH levels, putrescine production, and aguA gene abundance, and they highlight the possibility of developing an effective technique for reducing the metal uptake of wheat grains using biochar plus metal-immobilizing bacteria in metal-contaminated soils. | |||||
22882. 题目: Fe-modified biochar enhances microbial nitrogen removal capability of constructed wetland To improve the nitrogen removal capability of constructed wetlands, the biochar, produced from bamboo, activated with HCl and coated with Fe (FeCl3·6H2O), and then was added as a substrate into the systems. Three horizontal subsurface flow constructed wetlands (HSCWs) was established to treat the low C/N tailwater from the wastewater treatment plant: C-HSCW (quartz sand + soil), B-HSCW (quartz sand + soil + unmodified biochar), and FeB-HSCW (quartz sand + soil + Fe-modified biochar). Under different combinations of hydraulic retention time and nitrogen loading, the FeB-HSCW revealed extremely effective nitrogen removal, compared to the C-HSCW and B-HSCW. The highest removal efficiencies of NO3−-N (95.30%), TN (86.68%), NH4+-N (86.33%), NO2−-N (79.35%) and COD (63.36%) were obtained in FeB-HSCW with the hydraulic retention time of 96 h. and low influent nitrogen loading (C/N of 2.5). Nitrogen mass balance analysis showed that microbial processes played the most important role of nitrogen removal in HSCWs and the Fe-modified biochar significantly enhanced the microbial nitrogen removal. A total of 128.40 g nitrogen was removed by microorganisms in FeB-HSCW (average removal rate of 2.52 g N/(m3·d1)), much higher than that in other two HSCWs. The contributions of microorganisms, substrate storage and plant uptake on the total amount of nitrogen removal in the FeB-HSCW was 92.69%, 2.97% and 4.34%, respectively. Moreover, FeB significantly increased the abundances of genes involved in nitrogen removal. The copy numbers of bacterial 16S rRNA and amx, as well as of genes nirS, nirK, nosZ-I, nosZ-II, and hzsA were 1.3- to 27.8-fold higher in the FeB-HSCW than that in the other two HSCWs. Thus, Fe-modified biochar provides a feasible and effective amendment for constructed wetlands to improve the nitrogen removal, particularly nitrate-N, for low C/N wastewaters by enhancing the microbial nitrogen removal capacity (mainly of the denitrification). | |||||
22883. 题目: Global Measurements of Brown Carbon and Estimated Direct Radiative Effects Brown carbon (BrC) is an organic aerosol material that preferentially absorbs light of shorter wavelengths. Global‐scale radiative impacts of BrC have been difficult to assess due to the lack of BrC observational data. To address this, aerosol filters were continuously collected with near pole‐to‐pole latitudinal coverage over the Pacific and Atlantic basins in three seasons as part of the Atmospheric Tomography Mission. BrC chromophores in filter extracts were measured. We find that globally, BrC was highly spatially heterogeneous, mostly detected in air masses that had been transported from regions of extensive biomass burning. We calculate the average direct radiative effect due to BrC absorption accounted for approximately 7 to 48% of the top of the atmosphere clear sky instantaneous forcing by all absorbing carbonaceous aerosols in the remote atmosphere, indicating that BrC from biomass burning is an important component of the global radiative balance. | |||||
22884. 题目: Relative importance of greenhouse gases, sulfate, organic carbon, and black carbon aerosol for South Asian monsoon rainfall changes The contribution of individual aerosol species and greenhouse gases to precipitation changes during the South Asian summer monsoon is uncertain. Mechanisms driving responses to anthropogenic forcings need further characterization. We use an atmosphere‐only climate model to simulate the fast response of the summer monsoon to different anthropogenic aerosol types and to anthropogenic greenhouse gases. Without normalization, sulfate is the largest driver of precipitation change between 1850 and 2000, followed by black carbon and greenhouse gases. Normalized by radiative forcing, the most effective driver is black carbon. The precipitation and moisture budget responses to combinations of aerosol species perturbed together scale as a linear superposition of their individual responses. We use both a circulation‐based and moisture budget‐based argument to identify mechanisms of aerosol and greenhouse gas induced changes to precipitation, and find that in all cases the dynamic contribution is the dominant driver to precipitation change in the monsoon region. | |||||
22885. 题目: Decadal shifts in soil pH and organic matter differ between land uses in contrasting regions in China Soil organic matter (SOM) and pH are critical soil properties strongly linked to carbon storage, nutrient cycling and crop productivity. Land use is known to have a dominant impact on these key soil properties, but we often lack the ability to examine temporal trajectories across extensive spatial scales. Large-scale monitoring programmes provide the data to evaluate these longer-term changes, and under different climatic conditions. This study used data from Chinese soil surveys to examine changes in soil pH and SOM across different land uses (dry farmland, paddy fields, grassland, woodland, unused land), with surface soil (0–20 cm) collected in the periods 1985–90 (Survey 1; 890 samples) and 2006–10 (Survey 2; 5005 samples) from two contrasting areas. In the southern part of China the mean pH of paddy soils fell sharply over the two decades between surveys - from pH 5.81 to 5.19 (p < 0.001), while dry farmlands in the northern sampling area fell slightly (from pH 8.15 to 7.82; p < 0.001). The mean SOM content of dry farmland soil rose in both areas and the mean SOM of paddy fields in the southern area also rose (all p < 0.001). Woodland soil pH in the south showed an increase from 4.71 to 5.29 (p < 0.001) but no significant difference was measured in the woodlands of the northern area, although the trend increased. The SOM content of woodland top soils rose in the northern (p = 0.003) and southern (p < 0.001) study areas. The implications and potential causes of these changes over the two decade timespan between surveys are discussed and suggestions made as to how large scale soil sampling campaigns can be designed to monitor for changes and potential controlling factors. | |||||
22886. 题目: The effect of methane seeps on the bacterial tetraether lipid distributions at the Okinawa trough A recent study indicated that branched glycerol dialkyl glycerol tetraethers (brGDGTs) can also be produced in situ under methanotrophic/hypoxic conditions in lakes (Weber et al., 2018). However, the effect of dynamic methanotrophic activities in the widely-distributed seafloor methane seeps on brGDGTs distributions in global continent margins remains enigmatic. In this study, we firstly report the occurrence of in situ produced brGDGTs in cold seep environments, based on the analysis of tetraether lipid distributions in the authigenic carbonates collected from the northern section of the Okinawa Trough (OT). The abundance ratio of isoGDGTs to brGDGTs (Ri/b) was much lower in the authigenic carbonates (0.94 to 2.25) than that in their neighboring sediments (>10) and suspended particulate matter (>60). Such significant higher bacterial branched GDGTs ratios in the authigenic carbonates indicate its additional sources besides terrestrial and/or water column inputs. Specifically, the brGDGT (Ia), brGDGT (IIa) and brGDGT (IIa') appear to form in situ, and influenced by the methane flux significantly. Furthermore, the in situ formed brGDGTs are associated with anaerobic oxidation of methane (AOM)-related microbiotas based on the analysis of the undirected network. Our study highlights that the distributions of seafloor methane seeps could impact on the bacterial tetraether lipid distributions in ocean, which would hamper the universal application of brGDGT-based proxies for terrigenous organic carbon tracing and paleoclimate reconstruction in marine environments. | |||||
22887. 题目: Stimuli Responsive Mixed Matrix Polysulfone Ultrafiltration Membrane for Humic Acid and Photocatalytic Dye Removal Applications Current work discusses the synthesis and characterization of a pH and thermo-responsive poly (N-vinylcaprolactam-TiO2-acrylic acid) (VCL-TiO2-AA) polymer nanocomposite in various compositions of TiO2 and application of these nanocomposites for the modification of polysulfone (PSF) membranes. The stimuli responsive nanocomposite was directly blended to the membrane casting solution and this casting solution was used to synthesize membranes by phase inversion method. The modified membranes were analyzed for their hydrophilic, photocatalytic, pH, and thermo-responsive behavior. The membranes were characterized for their morphology by using FESEM. FTIR and FESEM-EDX analysis were carried out to analyze their elemental analysis. Furthermore, the effect of the synthesized stimuli responsive VCL-TiO2-AA polymer nanocomposite was analyzed on the membrane performance in terms of fouling, temperature and pH responsiveness, and photocatalytic removal of MB dye under dark and UV light conditions at different pH values. Furthermore, the ultrafiltration performance and antifouling nature of the modified membranes were investigated and analyzed. | |||||
22888. 题目: Has the formation of disinfection by-products been overestimated? Membrane leakage from syringe filter heads serves as unexpected precursors Syringe filters are widely used for sample pretreatments in laboratories. This study found that, surprisingly, these filters can leak dissolved organic carbon (DOC) that can potentially serve as precursors of disinfection by-products (DBPs). Nine common types of syringe filters were assessed. The results showed that the DOC of ultrapure water increased after syringe filtration. The DOC shed from filter membranes was characterized, whose spectra showed that the main compounds exhibited a low apparent molecular weight. Five classes of DBPs were investigated including trihalomethanes, haloacetaldehydes, haloacetonitriles, haloacetamides and halonitromethanes, among which trichloromethane (TCM), dichloroacetaldehyde (DCAL), trichloroacetaldehyde (TCAL), dichloroacetonitrile (DCAN), and trichloronitromethane (TCNM) were principally detected. The DBP formation was affected by chlorination time and membrane types. In general, the use of the poly vinylidene fluoride membrane resulted in the highest formation of TCM and TCAL, whereas nylon and mixed cellulose esters membranes contributed significantly to the formation of DCAN and TCNM, respectively. The shedding DOC and the formation of TCM, DCAL and TCAL from filter membranes were mitigated effectively by pre-washing; however, the contribution of membrane leakage to DCAN and TCNM formation was still notable, even with a pre-wash volume of 50 mL. When unwashed syringe filters were used for a real water sample, the DBP formation increased by up to 73.2% compared to the pre-washed ones; particularly for TCNM it was always over 15%. Therefore, for better quality control in laboratories, more attention should be paid to the syringe filters during sample pre-treatments, particularly when DBP formation is being investigated. | |||||
22889. 题目: Global variations and controlling factors of soil nitrogen turnover rate Soil nitrogen (N) availability, which is crucial to plant growth, largely relies on the turnover of soil organic N into inorganic N through mineralization. However, the patterns and drivers of global soil N turnover rates (NTR) have not been carefully examined so far. We compiled a dataset that consists of 1175 observations from 159 published articles across various terrestrial ecosystems in the world. Our analysis of this dataset showed that changes in soil NTR successfully predicted global NH4+–N content, a key indicator of soil N availability. Our analysis also revealed a clear latitudinal pattern of soil NTR, which was high in low latitude but low in high latitude. Soil NTR was greater in croplands than grasslands and wetlands. The dominant driving variables were mean annual temperature which accounted for 23% of the total variation in soil NTR. Soil clay content explained 15% of the total variation and it strongly inhibited soil NTR. However, the key driver in soil NTR differed with ecosystem type, i.e. soil microbial biomass in croplands, clay content in forests and grasslands, and soil C:N ratio in wetlands. This study highlights the importance of climatic factors and soil properties on soil NTR, which should be integrated into biogeochemical models to better predict the changes of soil N availability at the global scale. | |||||
22890. 题目: Soil aggregation and soil aggregate stability regulate organic carbon and nitrogen storage in a red soil of southern China Soil aggregation plays a critical role in the maintenance of soil structure, as well as in its productivity. Fertilization influences soil aggregation, especially by regulating soil organic carbon (SOC) and total nitrogen (TN) contents in aggregate fractions. The present study evaluated the influence of three contrasting fertilizer regimes (unfertilized control –CK-, mineral fertilization –NPK- and manure combined with NPK –NPKM) on soil aggregate stability, aggregate-associated organic carbon and total nitrogen sequestration and mineralization of SOC. Soil samples from (20 cm) depth were collected from a long-term fertilization experiment and analysed for size distribution ranging (>250 μm, 250-53 μm and <53 μm sizes), SOC and TN contents, as well as for mineralization of bulk and aggregate associated-SOC. Both NPK and NPKM fertilizations significantly enhanced SOC and TN contents in bulk soil and its constituent aggregates of >250 μm, 250-53 μm and <53 μm sizes, as compared to CK. Long-term NPK and NPKM increased SOC and TN stock in bulk soil by 45 and 98%, and by 70 and 144%, respectively, as compared to CK. Similarly, higher values of SOC and TN stock in all aggregate fractions was observed with the application of NPKM. Application of NPK and NPKM for 26 years significantly increased aggregate stability, which was positively correlated with total SOC contents in terms of mean weight diameter (MWD) (Adj. R2 = 0.689, p < 0.03) and geometric mean diameter (GMD) (Adj. R2 = 0.471, p < 0.24). Moreover, higher scores regarding cumulative mineralization for bulk soil and aggregate associated OC were observed with the application of NPK and NPKM. Irrespective of treatments, higher cumulative C-mineralization was observed for macro-aggregates (>250 μm size) followed by 250-53 μm and <53 μm size aggregates. Interestingly, a highly positive correlation was observed between aggregate stability and the cumulative amount of mineralization for bulk soil and aggregate fractions, with R2 ranging from 0.84 to 0.99. This study evidenced that long-term fertilization of NPK and NPKM can improve soil aggregation, stability and associated OC and TN stock in aggregates, as well as aggregate-associated OC mineralization, which was further governed by aggregate size. | |||||
22891. 题目: Winter rye does not increase microbial necromass contributions to soil organic carbon in continuous corn silage in North Central US There is insufficient evidence for how cover crop-driven changes to the soil microbial community affect soil organic carbon (SOC) accumulation. One mechanism by which enhanced microbial activity can contribute to SOC accrual is through the conversion of plant inputs to microbial biomass and ultimately necromass that may form organo–mineral associations with soil particles. Here we investigated the effects of winter rye as a cover crop and winter rye harvested as a forage double crop on SOC, chemically labile and complex C fractions, microbial necromass biomarkers (amino sugars), and potential extracellular enzyme activities following a seven–year continuous corn silage trial in southern Wisconsin, North Central US. Whereas SOC increased when winter rye was used as a cover crop compared to no cover, there were no changes to SOC when winter rye was harvested as a forage crop. A positive relationship between chemically labile aliphatic soil–C and total SOC indicates that higher SOC stocks may result from persistence of simple compounds rather than chemically complex, aromatic materials. However, the accumulation of microbial necromass, as inferred from amino sugar biomarker concentrations, was largely unaffected by winter rye use, despite a positive relationship between SOC and amino sugar residue concentrations. Greater potential extracellular enzyme activities indicates increased microbial activity with winter rye. Together, these results suggest that despite some microbial stimulation and potential soil health benefits, winter rye did not increase the contribution of microbial necromass to SOC accrual in this seven–year continuous corn silage field trial. | |||||
22892. 题目: Characterisation of dissolved organic matter to optimise powdered activated carbon and clarification removal efficiency | |||||
22893. 题目: Biochar-driven reduction of As(V) and Cr(VI): Effects of pyrolysis temperature and low-molecular-weight organic acids Batch experiments were conducted to examine the differential effects of biochar pyrolysis temperature and low-molecular-weight organic acids on the reduction of As(V) and Cr(VI) driven by Pennisetum hydridum biochar. The results showed that pyrolysis temperature significantly affected the reducing strength of the biochar. Biochar produced at 500 °C had a stronger electron-donating capacity than did the biochars produced at 300 and 700 °C. In the co-presence of the biochar and a low-molecular-weight organic acid, arsenic and chromium behaved differently. Oxalic acid and malic acid tended to have better effects on enhancing biochar-driven Cr(VI) reduction, as compared to citric acid while the opposite was observed for biochar-driven As(V) reduction. Biochar produced at 300 °C was more favourable for Cr(VI) reduction, as compared to the higher-temperature biochars while the opposite was observed for As(V) reduction in the presence of low-molecular-weight organic acids. This may make the lower-temperature biochar ideal for remediating contaminated soils containing both As(V) and Cr(VI) since it could maximize Cr(VI) reduction while minimizing As(V) reduction. | |||||
22894. 题目: Disentangling the drivers of Microcystis decomposition: Metabolic profile and co-occurrence of bacterial community In aquatic ecosystems, water microbial communities can trigger the outbreak or decline of cyanobacterial blooms. However, the microbiological drivers of Microcystis decomposition in reservoirs remain unclear. Here, we explored the bacterial community metabolic profile and co-occurrence dynamics during Microcystis decomposition. The results showed that the decomposition of Microcystis greatly altered the metabolic characteristics and composition of the water bacterial community. Significant variations in bacterial community composition were observed: the bacterial community was mainly dominated by Proteobacteria, Actinobacteria, Planctomycetes, and Bacteroidetes during Microcystis decomposition. Additionally, members of Exiguobacterium, Rhodobacter, and Stenotrophomonas significantly increased during the terminal stages. Dissolved organic matters (DOM) primarily composed of fulvic-like, humic acid-like, and tryptophan-like components, which varied distinctly during Microcystis decomposition. Additionally, the metabolic activity of the bacterial community showed a continuous decrease during Microcystis decomposition. Functional prediction showed a sharp increase in the cell communication and sensory systems of the bacterial communities from day 12 to day 22. Co-occurrence networks showed that bacteria responded significantly to variations in the dynamics of Microcystis decomposition through close interactions between each other. Redundancy analysis (RDA) indicated that Chlorophyll a, nitrate nitrogen (NO3−-N), dissolved oxygen (DO), and dissolved organic carbon (DOC) were crucial drivers for shaping the bacterial community structure. Taken together, these findings highlight the dynamics of the water bacterial community during Microcystis decomposition from the perspective of metabolism and community composition, however, further studies are needed to understand the algal degradation process associated with bacteria. | |||||
22895. 题目: Addition of softwood biochar to contaminated soils decreases the mobility, leachability and bioaccesibility of potentially toxic elements Softwood-derived biochar (5% w/w) was added to two mining soils (S1 and S2) contaminated with Cd (4.8–74 mg kg−1), Pb (318–1899 mg kg−1) and Zn (622–3803 mg kg−1), to evaluate its immobilization capabilities towards such potentially toxic elements (PTEs). Biochar addition (S + B) increased soil pH, organic carbon content, extractable phosphorous and calcium. Sequential extractions showed that biochar reduced the labile pools of PTEs (e.g. −29, 55 and 79% of water-soluble and exchangeable Cd, Zn and Pb respectively in S1 + B compared to S1) and at the same time increased their most stable and less mobile fractions. Leaching experiments revealed a significant decrease of DOC, N-NO3−, P and PTEs in biochar-treated soils, and an increase of leached K. Kinetic equations derived from leaching data showed that PTEs in control soils were quickly mobilized, while those in biochar-treated soils needed longer time to leachate. In vitro tests showed that biochar was effective at reducing the bioaccessibility of Cd and Pb in the gastric phase of S2 and that of Zn and Pb in the intestinal phase of S1. The results obtained showed that biochar could be used as alternative amendment for the recovery of PTEs-contaminated soils. | |||||
22896. 题目: Source identification and component characterization of dissolved organic matter in an acid mine drainage reservoir Acid mine drainage (AMD) is one of the most serious environmental problems and extreme environments on the earth, with high concentrations of sulphate and dissolved metals. A comprehensive description of dissolved organic matter (DOM) in these reservoirs is lacking, and it can play an important role in AMD pollution treatment and ecosystem. Thus, the source, composition and property of DOM in an AMD reservoir in Ma'an shan, China were studied using Fourier transform ion cyclotron resonance mass spectrometry and three-dimension excitation emission matrix fluorescence spectroscopy. The results suggested that the autochthonous algal metabolites significantly contributed to the DOM pool in the AMD reservoir. Bioavailable substances with lower oxidation, unsaturation and aromaticity such as lipids and carbohydrates were lacking in the AMD reservoir especially in the deeper layers. In addition, the proportion of sulfur compounds was significantly higher than that in other waters, suggesting the potential formation of organic matter with sulfur atom in a sulfur-rich environment. These findings underscore that the investigation of DOM in AMD reservoirs may offer references for the AMD treatment with addition of organic matter and broaden the understanding of special carbon cycling in the extreme environment of AMD. | |||||
22897. 题目: Bioprocessing strategies to increase the protein fraction of Rhizopus oryzae biomass using fish industry sidestreams The sidestreams produced during fish processing end in a separation tank where the resulting fractions follow biogas production or wastewater treatment. These streams can alternatively be used for production of protein-rich fungal biomass for e.g. fish feed applications, a product in increasing demand. These streams and upper streams originated during fish processing were used in this study for production of biomass using the edible filamentous fungus Rhizopus oryzae. The COD of the streams varied between 11 and 54 kg/m3 and, after fungal conversion of organic matter into protein-rich biomass and separation, a reduction of 34–69% was achieved. The stream origin had an effect on the final production and composition of the fungal biomass: 480 kg of biomass containing 33% protein per ton of COD were produced after cultivation in the separation tank streams, while 220 kg of biomass containing 62% protein per ton of COD were produced in upper sidestreams with lower amounts of suspended solids. Changing the initial pH (6.1–6.5) to 5.0 had a negative influence on the amount of biomass produced while medium supplementation had no influence. Thus, fish processing sidestreams can be diverted from biogas production and wastewater treatment to the production of protein-rich biomass for feed applications. | |||||
22898. 题目: Enhanced sludge dewaterability with sludge-derived biochar activating hydrogen peroxide: Synergism of Fe and Al elements in boichar Reuse of sludge-derived Fe-rich biochar as sludge conditioner is an attractive route for management of waste activated sludge at source. Homogeneous and heterogeneous Fenton reactions have been proved in sludge conditioning with Fe-rich biochar activating H2O2 to enhance sludge dewaterability. The FeAl2O4 phase in Fe-rich biochar was first identified during pyrolysis of sewage sludge after adding both Fe2O3 and Al2O3, since Fe and Al elements are two of major metal elements in Fe-rich sludge. Compared with the Fe-rich biochar that did not comprise FeAl2O4 phase, the capillary suction time (CST) and specific resistance to filterability (SRF) of the sludge conditioned with the Fe-rich biochar comprising FeAl2O4 phase could be efficiently decreased by 23% and 44%, respectively. The results indicated that FeAl2O4 phase in Fe-rich biochar could improve sludge dewaterability by enhancing heterogeneous Fenton reaction. Synergistic effect between Fe and Al in FeAl2O4 contributed to weak the O–O bond in H2O2 and reduce the activation energy of H2O2 decomposition for enhancing ·OH generation, which could be explained by density functional theory (DFT) calculations for the first time. Thus, the decomposition rate of H2O2 and the amount of ·OH generation were obviously promoted by FeAl2O4 phase in sludge-derived biochar during sludge conditioning, attributing to the destruction of sludge flocs, the release of bound water, and the improvement of sludge dewaterability. | |||||
22899. 题目: Microbial assimilation dynamics differs but total mineralization from added root and shoot residues is similar in agricultural Alfisols Microbial transformation of crop residue is the key process of soil organic matter (SOM) formation and mineralization, which determines soil fertility and affects global climate change. However, utilization dynamics of residue-derived carbon (residue C) by various microbial communities is still not well understood, especially under different residue quality and soil fertility conditions over a long-term scale (i.e., >1 year). In this study, a 500-day in-situ field experiment was conducted using 13C-labeled maize (Zea mays L.) root and shoot (composed of both stem and leaf) to examine the role of microbial community composition on the C processing. Specifically, the mineralization of residue C and incorporation of residue C into microbial biomass in low fertility (LF) and high fertility (HF) soils were investigated. The abundance of 13C in soil samples and microbial phospholipid fatty acids (PLFAs) were measured after 60, 90, 150 and 500 days since the residues added. The results showed that the mineralization rate of residue C was significantly higher in the LF than that in the HF soil for the first 150 days, and the shoot-derived C was more susceptible to degradation than root-derived C, but the final mineralization rates (∼78%) were not significantly different among treatments on the day 500. Soil fertility significantly affected the relative composition of different microbial groups and distribution of residue C in microbial communities, but residue type did not do so. Furthermore, residue C contributed more to PLFA-C pool in the LF than HF treatments, and the proportion of root C in PLFA-C pool was higher than that of shoot C, indicating easier immobilization of root C by soil microbial anabolism. Accordingly, soil fertility and residue quality could both regulate the kinetics of the microbial immobilization of crop residue C, but overall the available residual quantity of applied (plant-derived) C to enhance or maintain soil C pool did not depend on them in a long term in the agricultural Alfisols. | |||||
22900. 题目: Organic fragments newly released from heat-treated peat soils create synergies with dissolved organic carbon to enhance Cr(VI) removal Surface fires occur naturally or anthropogenically and can raise the temperature at the soil surface up to 600 °C. The heat derived from the surface fire can be subsequently transferred into CO2-enriched subsoils. As a result, the chemical compositions of soil organic matter (SOM) may be altered in fire-impacted anaerobic environments, indirectly influencing the redox transformations of pollutants, such as Cr(VI). In this study, a peat soil was heated up to 600 °C with limited air flow to simulate the effects of heat on the SOM during surface fire events. Then, Cr(VI) removal, including reduction and sorption, by the heat-treated peat soils was determined in relation to changes in the soil organic components. The results showed that the amount of O-containing functional groups, –CH2/–CH3 units of aliphatic groups, and dissolved organic carbon (DOC) in the SOM gradually decreased with an increase in the heating temperature. The removal of 0.1932 mM Cr(VI) did not exhibit a consistent decline along with the changes in these soil components. The heating temperatures of 200 and 250 °C were the thresholds that led to the decomposition of temperature-sensitive soil organic components such as lignin and other labile SOM. Such newly released organic fragments synergized lignin-like substances and carboxyl groups, resulting in up to 99% removal of the initially added Cr(VI). As the heating temperatures were increased from 300 to 600 °C, Cr(VI) reduction decreased from 66% to 20%. The black carbon-like materials and/or aromatic-containing moieties were the major components responsible for Cr(VI) reduction in 600°C-treated peat soils. | |||||
