17401. 题目: Pollution-induced slowdown of coarse woody debris decomposition differs between two coniferous tree species
期刊: Forest Ecology and Management
作者: Olesya V. Dulya, Igor E. Bergman, Vladimir V. Kukarskih, Evgenii L. Vorobeichik, Georgii Yu. Smirnov, Vladimir S. Mikryukov
摘要: Boreal forests store a large portion of the planet’s terrestrial carbon. A significant portion of this carbon is stored in coarse woody debris (CWD). Industrial pollution greatly inhibits organic matter decomposition and thus enhances carbon sequestration in the soil. However, little is known about the decomposition of CWD in polluted areas. In this work, by means of dendrochronological cross-dating, we determined the death dates of 90 downed Siberian spruce (Picea obovata Ledeb.) and Siberian fir (Abies sibirica Ledeb.) logs in the latest stages of decay in an undisturbed boreal forest and in two industrially polluted forests with 10-fold and more than 100-fold higher copper content in the soil. We found that, in the unpolluted area, the mean halftime of fir and spruce decomposition was 26 years and 23 years, respectively. In polluted areas, this time increased by approximately 16 years for fir and 5 years for spruce. Based on an exponential decay model, pollution caused a 16–60% decrease in the wood decomposition rate constant. Copper concentrations in CWD were similar between tree species and were about 10–20 times lower than in the surrounding soil. These values are comparable with the concentrations tolerated by fungi in laboratory tests, indicating that heavy metal excess cannot be considered a primary inhibitor of wood decomposer activity. The greater pollution-induced delay in the decomposition of fir trees, which are lighter and smaller in size than spruce trees, suggests that dead tree leaning is an important factor in the wood decomposition slowdown in polluted areas where stand density increases due to intensive forest regeneration because of the reduced competition of tree seedlings with toxically inhibited herbaceous vegetation.We also evaluated dynamic probing as a rapid, low-cost, and nondestructive surrogate of wood density measuring. Dynamic probing performed in the field on heavily decayed CWD explained about 40% of wood density variability and about 70% of variability when taking into account the gravimetrically measured wood moisture content. With negligible modifications, this method can be applied in the field monitoring of wood density loss. For the purpose of between-study comparisons, we recommend transforming the widely used measure of penetration depth to specific resistance to penetration and encourage the elaboration of reference tables that relate specific resistance to penetration and wood density for different tree species across distinct ecological zones.
17402. 题目: Are the combined effects of warming and drought on foliar C:N:P:K stoichiometry in a subtropical forest greater than their individual effects?
期刊: Forest Ecology and Management
作者: Qiufang Zhang, Jiacong Zhou, Xiaojie Li, Zhijie Yang, Yong Zheng, Jian Wang, Weisheng Lin, Jinsheng Xie, Yuehmin Chen, Yusheng Yang
摘要: Carbon (C), nitrogen (N), phosphorus (P), and, more recently, potassium (K) have been examined in ecological stoichiometry because they are the most abundant elements in organic matter. An increasing number of studies are investigating the potential responses of plants to future global climate change scenarios, and although warming and drought may greatly influence ecosystem function and services, their combined effects on C:N:P:K stoichiometry remain unknown. In the present study, we assessed the stoichiometry of a major subtropical tree species Cunninghamia lanceolata (Lamb.) Hook, in southern China in terms of its responses to warming and drought stresses. To measure C, N, P, and K concentrations, C:N:P:K stoichiometric ratios, and stable isotope abundance, we sampled C. lanceolata needles from seedlings subject to four treatments: control (CT), warming (W, with 5 °C increase in temperature), drought (D, with 50% decrease in precipitation), and the abovementioned warming and drought conditions combined (WD). The warming and drought conditions applied simulated the climate changes predicted for the next decades in southern China. We found that variations in foliar C:N:P:K stoichiometric ratios were driven by changes in nutrient concentration, season, and treatment. Unexpectedly, differences in foliar intrinsic water use efficiency across sampling seasons were not significant. The WD conditions increased foliar N concentration (57%) and the δ15N value (111%) across the different seasons, and significant interactive effects between warming and drought on foliar N concentration and δ15N were clearly demonstrated. The N cycle is likely to accelerate in subtropical forests, with more of the “heavier” N being mobilized for plant use, and thus the combination of warming plus drought may alleviate plant N restrictions in the future. Thus, foliar δ15N might be used as an indicator of the changes in N cycling in C. lanceolata forests.
17403. 题目: Digital soil mapping algorithms and covariates for soil organic carbon mapping and their implications: A review
作者: Sushil Lamichhane, Lalit Kumar, Brian Wilson
摘要: This article reviews the current research and applications of various digital soil mapping (DSM) techniques used to map Soil Organic Carbon (SOC) concentration and stocks following a systematic mapping approach from 2013 until present (18 February 2019). It is intended that this review of relevant literature will assist prospective researchers by identifying knowledge clusters and gaps in relation to the digital mapping of SOC. Of 120 studies, most were clustered in some specific countries such as China, Australia and the USA. The highest number publications were in 2016 and 2017. Regarding the predictive models, there was a progression from Linear Models towards Machine Learning (ML) techniques, and hybrid models in Regression Kriging (RK) framework performed better than individual models. Multiple Linear Regression (MLR) was the most frequently used method for predicting SOC, although it was outperformed by other ML techniques in most studies. Random Forest (RF) was found to perform better than MLR and other ML techniques in most comparative studies. Other common and competitive techniques were Cubist, Neural Network (NN), Boosted Regression Tree (BRT), Support Vector Machine (SVM) and Geographically Weighted Regression (GWR). Due to the inconsistency in various comparative studies, it would be advisable to calibrate the competitive algorithms using specific experimental datasets. This review also reveals the environmental covariates that have been identified as the most important by RF technique in recent years in regard to digital mapping of SOC, which may assist in selecting optimum sets of environmental covariates for mapping SOC. Covariates representing organism/organic activities were among the most frequent among top five covariates, followed by the variables representing climate and topography. Climate was reported to be influential in determining the variation in SOC level at regional scales, followed by parent materials, topography and land use. However, for mapping at a resolution that represents smaller areas such as a farm- or plot-scale, land use and vegetation indices were stated to be more influential in predicting SOC. Furthermore, unlike a previous review work, all recent studies in this review incorporated validation and 41% of them estimated spatially explicit prediction of uncertainty. Only 9.16% studies performed external validation, whereas most studies used data-splitting and cross-validation techniques which may not be the best options for datasets obtained through non-probability sampling.
17404. 题目: Perspectives on provenance and alteration of suspended and sedimentary organic matter in the subtropical Pearl River system, South China
期刊: Geochimica et Cosmochimica Acta
作者: Baozhi Lin, Zhifei Liu, Timothy I. Eglinton, Selvaraj Kandasamy, Thomas M. Blattmann, Negar Haghipour, Gert J de Lange
摘要: Large river systems accumulate, process, and transport huge quantities of organic matter (OM) from their catchments, part of which is exported to the ocean. Although this suite of processes comprises an important component of the global carbon cycle, integrated studies examining the nature and extent of OM processing on a basin-wide scale remain rare. Here, we provide an overview of provenance and composition of OM in suspended and deposited sediments within the Pearl River watershed in South China. We present new data on the organic carbon (OC) and total nitrogen (TN) contents, stable carbon and radiocarbon isotopic compositions of OC (δ13C and Fm), as well as grain size distribution and mineral-specific surface area of Pearl River sediments. These results are combined with published data on suspended particulate matter (SPM) and soil profiles in the Pearl River watershed in order to determine the provenance and transformation of OM in this large subtropical fluvial system.We find that the low 14C contents, expressed as fraction modern (Fm) values, in suspended (Fm: 0.58–0.87) and sedimentary OM (Fm: 0.38–0.82) are attributed to contributions from 14C-depleted soils, bedrock, as well as riverine primary productivity (Rpp) that utilizes 14C-depleted sources of dissolved inorganic carbon (DIC). For SPM, soil OM (Fm: 0.87±0.13) is inferred to be the dominant fraction during the wet season, whereas the contributions of Rpp (Fm: 0.86±0.04) and petrogenic OC (devoid of 14C) are enhanced during the dry season. This manifests itself in differences in OCsoil, OCRpp, and OCpetro contributions in SPM between wet and dry seasons (1.05±0.18 vs. 1.20±0.50%, 0.16±0.03 vs. 0.32±0.15% and 0.21±0.07 vs. 0.38±0.19%). During erosion and transport, the most labile OM in the top soil is rapidly degraded, as indicated by a stronger contribution from soil CO2 into riverine DIC during the wet season and flood event (39±1% and 45±3%) compared to the dry season (31±2%). River sediments are primarily accumulated during the wet season when suspended sediment fluxes are high. Refractory deep soil OM (Fm: 0.74±0.07) dominate in these sediments, whereas moderately labile soil OM components are further degraded during settling and storage. This sedimentary OM is predominantly composed of aged soil (92±4%), with a minor contribution from bedrock (7±4%) and negligible input from Rpp (0.2±0%). The longitudinal changes in the composition of suspended and sedimentary OM are mainly controlled by input of Rpp and ongoing degradation processes in the river system. The riverine particulate OC flux to the Pearl River estuary and ocean thus contains a mixture of soil, petrogenic and Rpp OM, all exhibiting relatively low Fm values. The riverine OM transformation and dynamics are important for the short-term carbon cycle, whereas the remaining signature and fate of the extensively processed, refractory OM has implications for the long-term carbon cycle.
17405. 题目: Distribution of copper-complexing ligands in Canadian Arctic waters as determined by immobilized copper(II)-ion affinity chromatography
期刊: Marine Chemistry
作者: Richard L. Nixon, Sarah L. Jackson, Jay T. Cullen, Andrew R.S. Ross
摘要: Complexation by dissolved organic ligands affects the bioavailability and distribution of copper and other bioactive trace metals in seawater. However, relatively little is known about the origin and identity of marine copper-complexing ligands, particularly in Arctic waters. We used immobilized copper(II)-ion affinity chromatography (IMAC) to isolate dissolved (< 0.2 μm) copper ligands from seawater samples collected during the 2015 Canadian Arctic GEOTRACES expedition. UV detection at 254 nm was employed to monitor elution of the compounds retained by IMAC. The areas of the resulting peaks were used to generate depth profiles that show, for the first time, how copper ligands are distributed across the Canadian Arctic. Copper ligand concentrations ranged from 0.9 to 4.8 nM, the depth of highest ligand concentration often coinciding with the chlorophyll maximum depth. Correlations between ligand concentration and in situ chlorophyll-a fluorescence suggest that marine phytoplankton or cyanobacteria could be an important source of copper ligands. A correlation was also observed between copper ligand and dissolved copper concentrations in Baffin Bay. Comparison of these results with published data for humic substances and other dissolved organic matter suggests that terrestrial input contributes to the pool of ligands captured by IMAC, particularly in the Canada Basin and Canadian Arctic Archipelago.
17406. 题目: Radiocarbon age of different photoreactive fractions of freshwater dissolved organic matter
期刊: Organic Geochemistry
作者: Naoto F. Ishikawa, David Butman, Peter A. Raymond
摘要: Dissolved organic carbon (DOC) plays a major role in aquatic carbon cycling. In order to determine if DOC photolability was related to DOC age, we tested the effect of oxidation time using UV irradiation on natural radiocarbon concentrations (Δ14C) of DOC in six US rivers. The most photo-labile DOC was 14C youngest. After a 100 min UV irradiation, most DOC (> 93%) was oxidized in two out of the six rivers studied. On the other hand, the other four rivers still had a considerable amount (> 20%) of DOC resistant to UV oxidation, which showed lower Δ14C values than those of bulk DOC. We also found that the concentration and Δ14C value of bulk DOC are controlled by the photochemically intermediate fraction. The results suggest that 14C age of organic matter is not homogeneous within DOC, the degree of which may depend on the characteristics unique to rivers.
17407. 题目: Treatability of hexabromocyclododecane using Pd/Fe nanoparticles in the soil-plant system: Effects of humic acids
期刊: Science of The Total Environment
作者: Thao Thanh Le, Hakwon Yoon, Min-Hui Son, Yu-Gyeong Kang, Yoon-Seok Chang
摘要: Hexabromocyclododecane (HBCD) is a persistent organic pollutant that accumulates in soil and sediments, however, it has been difficult to degrade HBCD with developed remediation technologies so far. In this study, degradation of HBCD by bimetallic iron-based nanoparticles (NPs) under both aqueous and soil conditions considering the effects of humic acids (HAs) and tobacco plant was investigated. In the aqueous solution, 99% of the total HBCD (15 mM) was transformed by Pd/nFe (1 g L−1) within 9 h of treatment and the HBCD debromination by Pd/nFe increased with the addition of HAs. In the soil system, 13%, 15%, 41% and 27% of the total HBCD were removed by treatments consisting of plant only, plant with HAs, plant with NPs and plant + NPs + HAs, respectively, compared to the HBCD removal in an unplanted soil. The 221–986 ng/g of HBCD were detected inside the plant after the treatments, and HAs showed considerable influence on the selective bioaccumulation of HBCD stereoisomers in the plant. Overall, this approach represents a meaningful attempt to develop an efficient and eco-friendly technology for HBCD removal, and it provides advantages for the sustainable remediation of recalcitrant emerging contaminants in soils.
17408. 题目: Changes in soil microbial biomass with manure application in cropping systems: A meta-analysis
期刊: Soil and Tillage Research
作者: Fengling Ren, Nan Sun, Meng Xu, Xubo Zhang, Lianhai Wu, Minggang Xu
摘要: Soil microbial biomass carbon (SMBC) and nitrogen (SMBN) are important indices of soil bio-fertility. While intensively managed cropping systems can reduce microbial biomass, application of manure is a potential way to rebuilt microbial biomass and improve soil functions. However, the responses of SMBC and SMBN to manure application relative to mineral fertilizers (NPK) in Chinese cropping systems remains unclear. We conducted a meta-analysis based on 103 peer-reviewed publications with 1448 paired observations to identify the degree to which climate types, soil properties and agricultural managements regulate the responses of microbial biomass to manure amendment relative to NPK. The results indicated that manure application increased SMBC, SMBN, SMBC/soil organic carbon (SOC) and SMBN/soil total nitrogen (TN) by 40%, 55%, 16% and 21%, respectively, across all the observations compared to NPK. SMBC/SMBN under manure amendment (6.58 in average) was lower than that in NPK (7.86 in average). Manure-related factors, e.g. manure types, duration of application, manure-C and N input rates, were the strongest regulators of the response of microbial biomass. Soil properties and climates also contributed to considerable degrees of variation in microbial biomass response based on variance partitioning analysis (VPA). Results of the random forest (RF) models showed that manure type, application rate (manure-C and N input) as well as soil initial properties (SOC, TN and clay contents) were likely the predominant factors controlling the response of microbial biomass to manure application. Our study indicates that manure application can be an effective way to restore the loss of microbial biomass due to intensive application of NPK, yet variations in response are determined by specific manure type, application rate, as well as local conditions of climate and inherent soil properties.
17409. 题目: Soil fauna promote litter decomposition but do not alter the relationship between leaf economics spectrum and litter decomposability
期刊: Soil Biology and Biochemistry
作者: Dunmei Lin, Fang Wang, Nicolas Fanin, Mei Pang, Pengpeng Dou, Hongjuan Wang, Shenhua Qian, Liang Zhao, Yongchuan Yang, Xiangcheng Mi, Keping Ma
摘要: The leaf economics spectrum (LES) describes co-variation in leaf functional traits relevant to carbon and nutrient economics across plant species. It has been proposed that LES can be a useful predictor of litter decomposability, thereby influencing ecosystem carbon and nutrient cycling. However, the role of soil fauna in mediating the LES-decomposability relationship is largely unexplored. We evaluated leaf litter decomposability of 21 co-occurring tree species in a subtropical forest in China. We used litterbags with different mesh sizes to control litter accessibility to meso- and macrofauna. We quantified 9 leaf functional traits and 12 litter traits, and investigated how these traits were related to the losses of litter mass, carbon and nitrogen under different fauna treatments. Litter mass loss varied from 32.3 to 80.6% after 400 days of decomposition in the field. Meso- and macrofauna presence increased on average litter mass loss by 8.4%, carbon loss by 11% and nitrogen loss by 14.4%. Litter nutrient contents and stoichiometry generally had no significant effect on decomposition rates. Instead, structure-related traits such as toughness, lignin and labile compounds were generally strongly related to decomposition rates, suggesting that decomposition processes are strongly limited by energy availability. We found significant linear relationships between LES and litter mass or carbon loss, but not nitrogen loss. However, meso- and macrofauna presence did not significantly alter the regression slopes of these relationships, suggesting that meso- and macrofauna exert similar effects on decomposition of litter originating from tree species characterized by different life strategies. This study advances our understanding of the soil fauna in driving litter decomposition in subtropical forests.
17410. 题目: Biomarker evidence for the occurrence of anaerobic ammonium oxidation in the eastern Mediterranean Sea during Quaternary and Pliocene sapropel formation
作者: Darci Rush, Helen M. Talbot, Marcel T. J. van der Meer, Ellen C. Hopmans, Ben Douglas, Jaap S. Sinninghe Damsté
摘要: The eastern Mediterranean Sea sedimentary record is characterised by intervals of organic-rich sapropel sediments, indicating periods of severe anoxia triggered by astronomical forcing. It has been hypothesised that nitrogen fixation was crucial in injecting the Mediterranean Sea with bioavailable nitrogen (N) during sapropel events. However, the evolution of the N biogeochemical cycle of sapropels is poorly understood. For example, the role of the complementary removal reactions like anaerobic ammonium oxidation (anammox) has not been investigated because the traditional lipid biomarkers for anammox, ladderane fatty acids, are not stable over long periods in the sedimentary record. Using an alternative lipid biomarker for anammox, bacteriohopanetetrol stereoisomer (BHT isomer), we present here for the first time N removal throughout the progression, e.g. formation, propagation, and termination, of basin-wide anoxic events. BHT isomer and ladderanes were analysed in sapropel records taken from three eastern Mediterranean sediment cores, spanning S1 to Pliocene sapropels. Ladderanes were rapidly degraded in sediments, as recently as the S5 sapropel. BHT isomer, however, was present in all sapropel sediments, as far back as the Pliocene, and clearly showed the response of anammox bacteria to marine water column redox shifts in high-resolution records. Two different N removal scenarios were observed in Mediterranean sapropels. During S5, anammox experienced Black Sea-type water column conditions, with the peak of BHT isomer coinciding with the core of the sapropel. Under the alternative scenario observed in the Pliocene sapropel, the anammox biomarker peaked at onset and termination of said sapropel, which may indicate sulfide inhibition of anammox during the core of sapropel deposition. This study shows the use of BHT isomer as a biomarker for anammox in the marine sediment record and highlights its potential in reconstructing anammox during past anoxic events that are too old for ladderanes to be applied, e.g. the history of oxygen minimum zone expansion and oceanic anoxic events.
17411. 题目: Enrichment of Lignin-Derived Carbon in Mineral-Associated Soil Organic Matter
期刊: Environmental Science & Technology
作者: Wenjuan Huang, Kenneth E. Hammel, Jialong Hao, Aaron Thompson, Vitaliy I. Timokhin, Steven J. Hall
摘要: A modern paradigm of soil organic matter proposes that persistent carbon (C) derives primarily from microbial residues interacting with minerals, challenging older ideas that lignin moieties contribute to soil C because of inherent recalcitrance. We proposed that aspects of these old and new paradigms can be partially reconciled by considering interactions between lignin decomposition products and redox-sensitive iron (Fe) minerals. An Fe-rich tropical soil (with C4 litter and either 13C-labeled or unlabeled lignin) was pretreated with different durations of anaerobiosis (0–12 days) and incubated aerobically for 317 days. Only 5.7 ± 0.2% of lignin 13C was mineralized to CO2 versus 51.2 ± 0.4% of litter C. More added lignin-derived C (48.2 ± 0.9%) than bulk litter-derived C (30.6 ± 0.7%) was retained in mineral-associated organic matter (MAOM; density >1.8 g cm–3), and 12.2 ± 0.3% of lignin-derived C vs 6.4 ± 0.1% of litter C accrued in clay-sized (<2 μm) MAOM. Longer anaerobic pretreatments increased added lignin-derived C associated with Fe, according to extractions and nanoscale secondary ion mass spectrometry (NanoSIMS). Microbial residues are important, but lignin-derived C may also contribute disproportionately to MAOM relative to bulk litter-derived C, especially following redox-sensitive biogeochemical interactions.
17412. 题目: Impact of a short heating event followed by rewetting on soil respiration and nutrient availability is not only due to soil drying during heating
期刊: Biology and Fertility of Soils
作者: Mihiri Seneviratne, Ashlea Doolette, Petra Marschner
摘要: Little is known about the impact of short-term heating to 50–100 °C as it may occur in fast-moving low-intensity fires on microbial activity and nutrient availability. Heating of soils usually induces drying, but it is unclear if the effect of heating is only due to this water loss or if other factors are also important. Two experiments were carried out where soils were heated to 60 °C. The experiments included constantly moist controls and air-dried soils which were dried at 30 °C to the same water content as the heated soils. After heating/air-drying, the soils were rapidly rewet and incubated for 2 weeks at a constant water content optimal for microbial activity. The aim of the first experiment was to assess the effect of water content before heating and heat duration on soil respiration and nutrient availability. Soil was incubated for 14 days at 33, 82, and 165 g water kg−1 (referred to as W33, W82, and W165, corresponding to 10, 30, and 50% maximum water-holding capacity) where 165 g water kg−1 is optimal for microbial activity in this soil. The soils were then heated to 60 °C and maintained at this temperature for 30 or 90 min. Heat duration had little effect on the measured properties. In heated soils, cumulative respiration after rewetting was about threefold higher than in the constantly moist control. Two days after heating, available N in heated soils was twofold higher than in the constantly moist control and 0.3 to twofold higher than the corresponding air-dried soils. Two weeks after heating, available N differed little between the constantly moist control and heated soils that were at W33 and W82 before heating, but it was about twofold higher in heated soil that was at W165 before heating. Available P 2 days after heating was highest in heated soils, but 2 weeks after heating, available P was lower in heated soils than the constantly moist control. In the air-dried controls which were dried at 30 °C to the same water content as in heated soils prior to rewetting, cumulative respiration, available N and P after rewetting differed little from the constantly moist soil. The aim of the second experiment was to determine the effect of soil nutrient content on soil respiration and nutrient availability after heating. Two soils differing in organic matter, total N, and total P content were used either separately or as mixes with different proportions of the soils. Soils were heated and maintained at 60 °C for 30 min. Before and after heating/air-drying, the soils were maintained at optimal water content (180 g water kg−1). Two and 7 days after heating, available N was 10–30% higher in heated soils than the constantly moist control and air-dried soils. It can be concluded that the effect of short-term heating followed by rewetting on soil respiration and available N and P is not only due to soil drying, but possibly also heating-induced changes in soil organic matter composition and availability as well as soil P sorption capacity.
17413. 题目: Ionic speciation and risks associated with agricultural use of industrial biosolid applied in Inceptisol
期刊: Environmental Monitoring and Assessment
作者: Isabel Cristina de Barros Trannin, Adriana Guirado Artur, José Oswaldo Siqueira, Fátima Maria de Souza Moreira
摘要: The evaluation of the chemical leaching potential from soils amended with biosolid is of extreme importance for environmental safety of agricultural use of these residues. The objective of this study was to evaluate the polluting potential and possible risks associated with the agricultural use of biosolids generated by the polyethylene terephthalate (PET) fiber and resin industry through ionic speciation and analysis of the activity of chemical species present in the leached solution from Inceptisol treated with rates 0, 6, 12, 18, 24, 48, 96, and 144 Mg ha−1 on dry basis. The experiment was conducted in a lysimeter and the treatments with three replications were distributed at random. Chemical leaching was made by application of CaC12 0.01 mol L−1 solutions in a volume fourfold higher than the water retention capacity of the soil, divided into five leaching events: 210, 245, 280, 315, and 350 days of incubation. Chemical species concentrations in collected leachates were used for ionic speciation by geochemical software Visual MINTEQA2 version 4.0. Impact factor of chemical species was calculated as the ratio between maximum concentration in the leach solution in the treated soil and control. Dissolved organic carbon had strong influence on Pb+2 and Cu+2 leaching, but these elements in free or complexed forms presented low activities in solution. Leaching of NO3−, Zn+2, and Na+ represents the main environmental risk of agricultural use of this residue. However, these risks can be minimized if technical criteria and critical limits for the agronomic use of biosolids were observed.
17414. 题目: High bacterial organic carbon uptake in the Eastern Tropical South Pacific oxygen minimum zone
期刊: Biogeosciences Discussions
作者: Marie Maßmig, Jan Lüdke, Gerd Krahmann, Anja Engel
摘要: Oxygen minimum zones (OMZs) show distinct biogeochemical processes that relate to microorganisms being able to thrive under low or even absent oxygen. Microbial degradation of organic matter is expected to be reduced in OMZs, although quantitative evidence is low. Here, we present heterotrophic bacterial production (3H leucine-incorporation), extracellular enzyme rates (leucine aminopeptidase/ß-glucosidase) and bacterial cell abundance for various in situ oxygen concentrations in the water column of the Eastern Tropical South Pacific off Peru. Bacterial heterotrophic activity in the suboxic core of the OMZ (at in situ ≤ 5 µmol O2 kg−1) ranged from 0.6 to 160 µmol C m−3 d−1 and was not significantly lower than in waters of 5–60 µmol O2 kg−1. Moreover, bacterial abundance in the OMZ was slightly and leucine aminopeptidase activity even significantly higher in suboxic waters compared to the upper oxycline suggesting no impairment of bacterial organic matter degradation in the core of the OMZ. Nevertheless, high cell-specific bacterial production and extracellular enzyme rates were observed in samples from the upper or lower oxyclines corroborating earlier findings of highly active and distinct micro-aerobic bacterial communities. To assess the impact of bacterial degradation of dissolved organic matter for oxygen loss in the Peruvian OMZ, we compared diapycnal fluxes of oxygen and dissolved organic carbon (DOC) and their microbial uptake within the upper 60 m of the water column. Our data indicate bacterial growth efficiencies of 0.5–8.6 % at the upper oxycline, resulting in a high bacterial oxygen demand that can explain up to 33 % of the observed average oxygen loss over depth. Our study therewith shows that microbial degradation of DOM has a considerable share in sustaining the OMZ off Peru.
17415. 题目: Comparison With Global Soil Radiocarbon Observations Indicates Needed Carbon Cycle Improvements in the E3SM Land Model
期刊: Journal of Geophysical Research: Biogeosciences
作者: Jinsong Chen, Qing Zhu, William J. Riley, Yujie He, James T. Randerson, Susan Trumbore
摘要: We evaluated global soil organic carbon (SOC) stocks and turnover time predictions from a global land model (ELMv1‐ECA) integrated in an Earth System Model (E3SM) by comparing them with observed soil bulk and Δ14C values around the world. We analyzed observed and simulated SOC stocks and Δ14C values using machine learning methods at the Earth System Model grid cell scale (~200 km). In grid cells with sufficient observations, the model provided reasonable estimates of soil carbon stocks across soil depth and Δ14C values near the surface but underestimated Δ14C at depth. Among many explanatory variables, soil albedo index, soil order, plant function type, air temperature, and SOC content were major factors affecting predicted SOC Δ14C values. The influences of soil albedo index, soil order, and air temperature were primarily important in the shallow subsurface (≤30 cm). We also performed sensitivity studies using different vertical root distributions and decomposition turnover times and compared to observed SOC stock and Δ14C profiles. The analyses support the role of vegetation in affecting soil carbon turnover, particularly in deep soil, possibly through supplying fresh carbon and degrading physical‐chemical protection of SOC via root activities. Allowing for grid cell‐specific rooting and decomposition rates substantially reduced discrepancies between observed and predicted Δ14C values and SOC content. Our results highlight the need for more explicit representation of roots, microbes, and soil physical protection in land models.
17416. 题目: Sorption of iodine in soils: insight from selective sequential extractions and X-ray absorption spectroscopy
期刊: Environmental Science and Pollution Research
作者: Fabian Köhler, Beate Riebe, Andreas C. Scheinost, Claudia König, Alex Hölzer, Clemens Walther
摘要: The environmental fate of iodine is of general geochemical interest as well as of substantial concern in the context of nuclear waste repositories and reprocessing plants. Soils, and in particular soil organic matter (SOM), are known to play a major role in retaining and storing iodine. Therefore, we investigated iodide and iodate sorption by four different reference soils for contact times up to 30 days. Selective sequential extractions and X-ray absorption spectroscopy (XAS) were used to characterize binding behavior to different soil components, and the oxidation state and local structure of iodine. For iodide, sorption was fast with 73 to 96% being sorbed within the first 24 h, whereas iodate sorption increased from 11–41% to 62–85% after 30 days. The organic fraction contained most of the adsorbed iodide and iodate. XAS revealed a rapid change of iodide into organically bound iodine when exposed to soil, while iodate did not change its speciation. Migration behavior of both iodine species has to be considered as iodide appears to be the less mobile species due to fast binding to SOM, but with the potential risk of mobilization when oxidized to iodate.
17417. 题目: Insights into interactions between vanadium (V) bio-reduction and pentachlorophenol dechlorination in synthetic groundwater
期刊: Chemical Engineering Journal
作者: Baogang Zhang, Yutong Cheng, Jiaxin Shi, Xuan Xing, Yuling Zhu, Nan Xu, Jianxin Xia, Alistair G.L. Borthwick
摘要: Aquifer co-contamination by vanadium (V) and pentachlorophenol (PCP) involves complicated biogeochemical processes that remain poorly understood, particularly from the perspective of microbial metabolism. Batch experiment results demonstrated that V(V) and PCP could be competitively bio-reduced, with 96.0 ± 1.8% of V(V) and 43.4 ± 4.6% of PCP removed during 7 d operation. V(V) was bio-transformed to vanadium (IV), which could precipitate naturally under circumneutral conditions, facilitating the removal of up to 78.2 ± 3.1% dissolved total V. The PCP reductive dechlorination products were mainly 2,4,6-trichlorophenol and 4-monochlorophenol with lower toxicity. High-throughput 16S rRNA gene sequencing indicated that Pseudomonas, Soehngenia, and Anaerolinea might be responsible for the two bio-transformations, with detected functional genes of nirS and cprA. Extracellular reduction by cytochrome c and intracellular conversion by nicotinamide adenine dinucleotide (NADH) occurred for both V(V) and PCP. Extracellular proteins in microbial-secreted extracellular polymeric substances (EPS) might also be involved in these enzymatic bioprocesses. EPS could protect microbial cells through V(V) binding by the chemically reactive carboxyl (COO−), and hydroxyl (–OH) groups. These findings elucidate the metabolic processes during anaerobic V(V) and PCP biotransformation, advance understanding of their biogeochemical fates, and provide a foundation on which to develop novel strategies for remediation of co-contaminated aquifers.
17418. 题目: Exploring the ecology of the mesopelagic biological pump
期刊: Progress in Oceanography
作者: E.L. Cavan, E.C. Laurenceau-Cornec, M. Bressac, P.W. Boyd
摘要: The oceans’ biological pump (BP) exports large amounts of particulate organic carbon (POC) to the mesopelagic zone (base of the euphotic zone – 1000 m depth). The efficiency at which POC is transferred through the mesopelagic zone determines the size of the deep ocean carbon store. Few observational BP studies focus on the mesopelagic, often leading to the need to oversimplify the representation of processes within this depth horizon in numerical models. In this review, we identify and describe three interlinked biological processes that act to regulate and control the transfer efficiency of POC through the mesopelagic zone; 1) direct sinking of phytoplankton cells and aggregates, 2) zooplankton community structure and 3) the microbial loop and associated carbon pump. We reveal previously unidentified relationships between planktonic community structure and POC transfer efficiency for specific regions. We also compare mesopelagic POC remineralisation depth (a proxy for POC transfer efficiency) with the permanent thermocline in different regions. Our analysis shows that even when mesopelagic POC transfer efficiency is low, such a transfer efficiency does not necessarily mean low carbon sequestration if the permanent thermocline is shallow, and we define a carbon sequestration ratio (Cseq, the remineralisation depth divided by the permanent thermocline) to highlight this. Low latitude regions typically have a higher Cseq than temperate and polar regions, and thus could be more important in transferring carbon on long timescales than previously thought. POC transfer efficiency should be regularly discussed in the context of the physical water properties such as the permanent thermocline, to truly assess an oceanic region’s ability to sequester carbon. Improved understanding of mesopelagic ecological processes and links to surface processes will better constrain ecosystem models and improve projections of the future global carbon cycle.
17419. 题目: Labile organic matter intensifies phosphorous mobilization in paddy soils by microbial iron (III) reduction
作者: Imran Khan, Shah Fahad, Lei Wu, Wei Zhou, Peng Xu, Zheng Sun, Abdus Salam, Muhammad Imran, Mengdie Jiang, Yakov Kuzyakov, Ronggui Hu
摘要: Iron (Fe) is one of the most abundant elements in the earth's crust and intensively interferes with the biogeochemical cycles of carbon (C) and phosphorous (P), especially in highly weathered tropical and subtropical soils. The strong affinity of phosphate to Fe oxides and hydroxides limits the P availability in paddy soils. Reductive dissolution of Fe(III) can release occluded and adsorbed P into solution and make it available for plant uptake. Such effects remain elusive, especially in highly weathered subtropical paddy soils with oscillating redox (Eh) conditions. Under submerged conditions, incomplete litter decomposition occurs and rice roots release large amounts of labile organic compounds as exudates. We investigated the role of acetate, formate, oxalate, and propionate on Fe(III) reduction, P mobilization, and CO2 efflux in two paddy soils (i.e. oxisol and ultisol) of varying organic C (OC) and Fe(II) contents. Microbial mineralization of added labile C decreased soil Eh and increased the rates of Fe(III) reduction followed by P mobilization. This indicated that microbially-mediated Fe(III) reduction was intensified by labile OC compounds, which acted as energy sources and electron donors. The release of available P via Fe reduction was accompanied by peaks in Fe(II), dissolved OC, and pH and was followed by a decrease in iron-bound P (FeP). This implied that FeP was the main source of available P in the paddy soils. The faster release of available P in the oxisol than the ultisol indicated that the higher OC and Fe(II) contents in the oxisol allowed a fast Eh decrease, leading to rapid microbial oxygen (O2) consumption and consequently faster and more intensive Fe(III) to Fe(II) reduction. This conclusion is supported by a faster Eh decrease in the oxisol than the ultisol corresponding to early P mobilization after input of labile C, and it suggests that Eh-driven Fe transformations and P mobilization are strongly modulated by labile OC mineralization.
17420. 题目: Effects of extracellular polymeric substances and microbial community on the anti-scouribility of sewer sediment
期刊: Science of The Total Environment
作者: Daizong Meng, Jun Wu, Keli Chen, Huaizheng Li, Wei Jin, Shuzhen Shu, Jin Zhang
摘要: Sewer sediment is the main source of overflow pollution, and the anti-scouribility of sewer sediment directly determines the amount of the discharged contaminants. In this study, sewer sediments of different depths were collected from combined and storm sewers in Shanghai, China. The anti-scouribility, represented by the shear stress of each layer of sewer sediment, was detected in situ. The microbial community and extracellular polymeric substances (EPS), including carbohydrates and proteins present in the sewer sediments were characterized. The results indicated that the distribution of the anti-scouribility of sewer sediment is regulated. There were positive correlations between the content of EPS, proteins, and carbohydrates, and the anti-scouribility of sediments (Pearson Corr. = 0.604, sig. = 0.219; Pearson Corr. = 0.623, sig. = 0.234; Pearson Corr. = 0.727, sig. = 0.359, respectively). Furthermore, the microbial community had a positive influence on anti-scouribility. In particular, the gram-positive bacterial phyla of Bacteroidetes and Firmicutes may be important and influential for the improvement of anti-scouribility of sediment owing to their production of cellulose.