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The Arctic is a critical region in terms of global warming. Environmental changes are already progressing steadily in high northern latitudes whereby, among other effects, a high potential of enhanced methane (CH4) emissions is induced. With CH4 being a potent greenhouse gas, additional emissions from Arctic regions may intensify global warming in the future by positive feedback. Various natural and anthropogenic sources are currently contributing to the Arctic's CH4 budget; however the quantification of those emissions remains challenging. Assessing the amount of CH4 emissions in the Arctic and their contribution to the global budget still remains challenging. This is on the one hand due to the difficulties in carrying out accurate measurements in such remote areas. Besides, high variations in the spatial distribution of methane sources and a poor understanding of the effects of ongoing changes in carbon decomposition, vegetation and hydrology also complicate the assessment. Therefore, the aim of this work is to reduce uncertainties on current bottom-up estimates of CH4 emissions as well as soil oxidation by implementing an inverse modeling approach in order to better quantify CH4 sources and sinks for the most recent years (2008 to 2019). More precisely, the objective is to detect occurring trends in the CH4 emissions and potential changes in seasonal emission patterns. The implementation of the inversion included footprint simulations obtained with the atmospheric transport model FLEXPART, various emission estimates from inventories and land surface models as well as data of atmospheric CH4 concentrations from 42 surface observation sites in the Arctic nations. The results of the inversion showed that the majority of the CH4 sources currently present in high northern latitudes are poorly constrained by the existing observation network. Therefore, conclusions on trends and changes in the seasonal cycle could not be obtained for the corresponding CH4 sectors. Only CH4 fluxes from wetlands are adequately constrained, predominantly in North America. Within the period under study, wetland emissions show a slight negative trend in North America and a slight positive trend in East Eurasia. Overall, the estimated CH4 emissions are lower compared to the bottom-up estimates but higher than similar results from global inversions. [ABSTRACT FROM AUTHOR]

Increasing the productivity of organic farming is a strategy to achieve sustainable agriculture. However, it is necessary to maintain soil redox potential (ORP) in continuously oxidized conditions and to promote bacterial metabolisms in soils to increase productivity. Previously, applying microbial fuel cell technology (MFCT) into sediment improved ORP and benthos survival in the sediment. It is thought that these positive effects of MFCT can also provide many benefits for soil cultivation in organic farming. This study aims to examine the changes in the biochemical properties of soil following MFCT application. In laboratory experiments, MFCT was applied to cow manure compost-mixed andosol. An anode (oxidation reaction) and a cathode (reduction reaction) were installed in the soil, and a 1.5-V solar cell was used to produce an electric current between the two electrodes. Three months after MFCT application, the chemical properties and adenosine triphosphate (ATP) of the soil were measured. Our results showed an electric potential distribution in the soil, and the soil located within 20 cm of the electrode was strongly affected by the electrode reaction. This suggests that applying MFCT to soil can change the soil's redox conditions. The ATP and ammonium concentrations increased, suggesting bacterial activation and enhanced organic matter decomposition in the soil. It is recommended that farmers should apply MFCT into soils for enhancing bacterial metabolism and increasing organic matter decomposition in soils. [ABSTRACT FROM AUTHOR]

Soil chemical environment (SCE) affects soil degradation and productivity, thus understanding of the temporal changes of SCE is important for obtaining higher soil productivity. Widely used indices of SCE included ion concentration, pH, and redox potential (ORP), but these cannot monitor SCE continuously. Previously, a study proved that continued potential measurement can represent temporal changes in the water quality at the sea floor. However, no report related to monitoring the SCE with continued potential measurement has been found. Therefore, this study proposes a method for evaluating soil ORP using continued potential measurement, and examine the method’s validity in representing changes in SCE due to soil reduction, bacteria activation, and soil oxidation. Laboratory experiments were conducted using soils from rice paddy fields. A brush-type carbon electrode was installed in the soil layer that then connected to a reference electrode for measurement of the soil ORP. Different soil conditions were created by mixing the paddy soil with cow manure compost or potassium sulfate. The soil ORP was automatically recorded every 15 min using a voltage meter. The ORP of paddy soil decreased temporally and stabilized at 50 days after the start of the experiment, suggesting that soil reduction occurred over those 50 days. When testing the potassium sulfate-paddy soil mixture, the soil ORP rapidly decreased during the first day after the experiment started. When testing cow manure compost-paddy soil mixture, a larger decrease in soil ORP was observed compared to that in the paddy soil alone. These findings suggest that soil reduction is promoted by adding potassium sulfate or cow manure compost. Among the soil samples tested, there was a range of soil ORPs and trends in the potential decreases. Based on the results of this study, it was found that continued potential measurement is effective in evaluating soil ORP, which represents temporal changes in SCE due to redox reactions after the addition of cow manure compost or potassium sulfate. In addition, the effects of bacteria activation are revealed during continued potential measurement of soil ORP. [ABSTRACT FROM AUTHOR]

Dependencies of temperature and injection level on carrier lifetimes in 50 μm thick p-type and n-type 4H-SiC epilayers have been investigated. The carrier lifetimes have been measured by differential microwave photoconductance decay measurements at various injection levels and temperatures. In both p-type and n-type epilayers, the carrier lifetimes gradually increased with increasing the injection level, which were naturally expected from the Shockley-Read-Hall (SRH) model, and after taking a maximum, the lifetimes dropped at the very high-injection level. In contrast, the carrier lifetimes exhibited continuous increase with elevating the temperature for both epilayers. In addition, the impact of thermal oxidation process on the carrier lifetimes has been also investigated. The thermal oxidation process, by which the Z1/2 and EH6/7 centers were remarkably reduced that had been observed in n-type 4H-SiC in our previous work, led to the improvement of the carrier lifetimes especially for n-type epilayers. The carrier lifetime reached 4.1 μs in p-type and 6.1 μs in n-type epilayers at 250 °C with an injection level of 1.8×1016 cm-3 through the thermal oxidation processing. [ABSTRACT FROM AUTHOR]

Environmental changes can alter the interactions between biotic and abiotic ecosystem components in tidal wetlands and therefore impact important ecosystem functions. The objective of this study was to determine how saltwater intrusion affects wetland nutrient biogeochemistry, with a specific focus on the soil microbial communities and physicochemical parameters that control nitrate removal. Our work took place in a tidal freshwater marsh in South Carolina, USA, where a 3.5-year saltwater intrusion experiment increased porewater salinities from freshwater to oligohaline levels. We measured rates of denitrification, soil oxygen demand, and dissimilatory nitrate reduction to ammonium (DNRA) and used molecular genetic techniques to assess the abundance and community structure of soil microbes. In soils exposed to elevated salinities, rates of denitrification were reduced by about 70% due to changes in the soil physicochemical environment (higher salinity, higher carbon:nitrogen ratio) and shifts in the community composition of denitrifiers. Saltwater intrusion also affected the microbial community responsible for DNRA, increasing the abundance of genes associated with this process and shifting microbial community composition. Though rates of DNRA were below detection, the microbial community response may be a precursor to increased rates of DNRA with continued saltwater intrusion. Overall, saltwater intrusion reduces the ability of tidal freshwater marshes to convert reactive nitrogen to dinitrogen gas and therefore negatively affects their water quality functions. Continued study of the interrelationships between biotic communities, the abiotic environment, and biogeochemical transformations will lead to a better understanding of how the progressive replacement of tidal freshwater marshes with brackish analogues will affect the overall functioning of the coastal landscape. [ABSTRACT FROM AUTHOR]

Abstract The isolation of acid-adapted ammonia-oxidizing bacteria (AOB) has suggested the functional importance of AOB in acidic soils. However, there is, currently, no convincing evidence that links AOB activity to nitrification in acidic paddy soils. Here we demonstrated the incorporation of 13CO 2 into the genomes of ammonia-oxidizing archaea (AOA), AOB and nitrite-oxidizing bacteria (NOB) following urea application by using stable isotope probing (SIP) in three acidic terrace paddy soils with altitudes of 200 m (E200), 600 m (E600) and 1100 m (E1100), respectively. Nitrification activity increased from E200 to E600 and then to E1100, accompanied with significant growth of AOB over the 56-day incubation, while the abundance of archaeal amoA gene declined significantly in all soils after incubation. DNA-SIP demonstrated that active AOB outnumbered AOA and were much more heavily labeled than AOA and NOB, implying their more significant contributions to nitrification in these soils. Phylogenetic analysis indicated that Nitrosospira cluster 3-like AOB predominantly catalyzed bacterial ammonia oxidation. 13C-labeled NOB was dominated by Nitrospira moscoviensis in E1100, while in E200 and E600, Nitrospira marina and Nitrospira japonica were as prevalent as Nitrospira moscoviensis , respectively. Canonical correlation analysis and the Mantel test indicated the importance of soil physiochemical properties (e.g., pH, available phosphorus (AP) and soil oxidation capacity (OXC)) in determining the composition of the active nitrifying populations. These results suggest a greater functional importance of AOB in ammonia oxidation in the tested acidic paddy soils and the existence of a broader ecological niche for AOB than previously considered. Highlights • Nitrification activity increased with the elevated altitudes. • AOB rather than AOA dominated nitrification activity in the acidic paddy soils. • Phylogenetically distinct NOB groups dominated nitrite oxidation in terrace soils. • Soil properties played a vital role in shaping the composition of active nitrifiers. [ABSTRACT FROM AUTHOR]

In West Sumatra, Indonesia, a high-yield perennial rice cropping method called SALIBU was recently reported, in which the most unique feature is double cutting (DC) at harvest and after harvest. The objective of this study was to verify the ratooning rice yield under the SALIBU system in Myanmar. Two cultivation trials consisting of two cutting and three moisture treatments were conducted in 2019 and 2020. We concluded that double cutting had no positive effect on grain yield and regeneration rate compared with single cutting (SC). For the cutting regime, significant results were detected in the ratoon crops on yield components, but all of these were negative effects of DC, and were statistically lower than those of SC. On the other hand, a significant positive effect of moisture regime on grain yield in all ratoons was observed. The grain yield of the dry regime was significantly increased by 69% compared with that of the saturated regime. Soil oxidation conditions during the initial growth period of ratoons could contribute to the improved yield performance of the ratoons.

Rice paddies are considerable sources of methane because of the highly reduced soil oxidation–reduction conditions during rice cultivation. In this ecosystem, active methane-oxidizing bacteria are important, because they consume methane while reducing the overall emissions from rice paddy soils. However, the biogeographic distribution of active methanotrophs in paddy soils across Taiwan remains poorly understood. We used DNA-based stable isotope probing (DNA-SIP) to show that phylogenetically distinct type I and type II methanotrophs dominated methane oxidation in geographically different paddy soils across Taiwan. High-throughput sequencing of soil 16S rRNA and pmoA genes under field conditions revealed that a type II methanotroph, Methylocystis , was predominant in rice paddy soils. In addition, an uncultured novel type I methanotroph cluster (Rice Paddy Clusters) was detected with the closest relatedness to Methylocaldum 16S rRNA genes in all rice field soils tested. SIP microcosm incubation, however, suggested that the type I methanotrophs Methylosarcina and Methylobacter were significantly stimulated during the consumption of high-concentration methane in five paddy soils with pH > 6.07, whereas the Methylosinus -like microorganisms of type II methanotrophs dominated aerobic methane-oxidizing communities in acidic soil with pH = 5.17. Furthermore, high-throughput sequencing of 13 C- pmoA genes indicated the presence of novel methanotrophs that are phylogenetically distantly related to the type I methanotrophs Methylosarcina in four out of five non-acidic paddy soils studied, and the high proportions in the 13 C-DNA suggested that these uncultured methanotrophs play an important role in methane oxidation. These results provide strong evidence for the environmental selection of phylogenetically distinct methanotrophs under field conditions. Moreover, community shifts in active methanotrophs likely occurred in response to environmental variations with fluctuating methane concentrations. [ABSTRACT FROM AUTHOR]

Lithospheric organic carbon ( “ petrogenic ” ; OC petro ) is oxidized during exhumation and subsequent erosion of mountain ranges. This process is a considerable source of carbon dioxide (CO2) to the atmosphere over geologic time scales, but the mechanisms that govern oxidation rates in mountain landscapes are poorly constrained. We demonstrate that, on average, 67 ± 11% of the OC petro initially present in bedrock exhumed from the tropical, rapidly eroding Central Range of Taiwan is oxidized in soils, leading to CO2 emissions of 6.1 to 18.6 metric tons of carbon per square kilometer per year. The molecular and isotopic evolution of bulk OC and lipid biomarkers during soil formation reveals that OC petro remineralization is microbially mediated. Rapid oxidation in mountain soils drives CO2 emission fluxes that increase with erosion rate, thereby counteracting CO2 drawdown by silicate weathering and biospheric OC burial. [ABSTRACT FROM AUTHOR]

Net methane (CH4) flux across the ecosystem-atmosphere boundary is governed by two counteracting processes, CH4 oxidation and production. Recent research on CH4 cycling has focused on net CH4 fluxes, however, the separate processes of CH4 oxidation and production may vary at local scales and respond differently to environmental change. Here, we separate CH4 oxidation and production, measured as emission, in situ using CH4 oxidation inhibition combined with a novel in situ 13CH4 labeling experiment to determine the rate of soil oxidation of atmospheric CH4. The study was conducted in a subarctic heath ecosystem with three characteristic plant community types: moist mixed species heath, dry Carex-dominated heath, and wet Eriophorum-dominated fen. We further explored the projected climate change effects of increased temperature and enhanced leaf litter input. The CH4 oxidation inhibition experiment revealed significant potential CH4 emission despite net CH4 uptake. Total CH4 oxidation and potential CH4 emission rates differed significantly between plant communities, demonstrating high local-scale variation in CH4 fluxes. Climate treatments did not affect CH4 oxidation rates, however, warming tended to increase potential CH4 emission, indicating that climate change may affect oxidation and production rates asymmetrically. Near-surface soil oxidation of atmospheric CH4 was successfully traced using 13C stable isotope labeling in situ. CH4 oxidation rates ranged widely, yet preliminarily suggested some degree of substrate limitation. Accounting for the local-scale variation in CH4 fluxes and the relative importance of the separate processes of CH4 oxidation and production will contribute importantly to predicting changes in landscape-scale CH4 budgets and climate feedbacks. [ABSTRACT FROM AUTHOR]

Purpose: This study investigates the effects of surface liming on soil attenuation radiation properties. For this, measurements of soil chemical attributes (pH, organic carbon, H+Al, Al3+, Ca2+, and Mg2+) and attenuation radiation parameters (mass attenuation coefficient, μm, atomic and electronic cross sections, σa and σe, effective atomic number and electron density, Zeff and Nel) were carried out. This aim was motivated by the fact that possible μm variation might cause as well variation in the determination of soil physical properties.Materials and methods: The studied soil, classified as a Dystrudept sity-clay, is located in South Brazil. The trial consisted of five stripes, one of them under pasture and the remaining under no-till system (NTS). Lime rates of 0, 10, 15, and 20 t ha−1 were broadcast on the NTS soil surface. Disturbed soil samples were collected 30 months after liming at the top (0-10 cm) and subsoil (10-20 cm) layers. Soil chemical attributes were characterized following standard experimental procedures. The soil oxide composition, obtained by EDXRF analysis, was used to calculate μm for 241Am and 137Cs photon energies with XCOM computer code. μm values were employed to calculate σa, σe, Zeff, and Nel and to predict variations in soil bulk density (ρ) and total porosity (φ).Results and discussion: Surface liming notably increased contents of soil pH, Ca2+, and Mg2+ while reduced H+Al and Al3+ at the top soil layer, where μm, σa, σe, and Zeff were also increased with the lime rates. However, at the subsoil layer, liming neither lessened soil acidity nor induced remarkable changes in the attenuation parameters. When using 137Cs photon energy, incoherent scattering totally dominated over the radiation interaction processes whereas photoelectric absorption and coherent scattering substantially contributed when 241Am photon energy was used. Therefore, the increasing in soil attenuation parameters at the top soil layer was more accentuated considering 241Am than 137Cs photon energy. Variation in μm caused considerable variation in ρ and φ only for 241Am photon energy.Conclusions: The findings regarding the effect of μm variation induced by liming on the determination of soil physical properties are extremely relevant because traditionally, in the soil science area, μm values are calculated without considering any chemical modification to which the soil can be submitted. Bearing in mind that ρ and φ are important parameters from the agricultural and environmental points of view, not representative measurements of μm can lead to biased values of ρ and φ. [ABSTRACT FROM AUTHOR]

The impact of remediation combining chemical oxidation followed by biological treatment on soil matrix and microbial community was studied, of a chronically hydrocarbon contaminated soil sourced from a landfarming treatment. Oxidation by ammonium persulfate produced a significant elimination of polycyclic aromatic hydrocarbons (PAHs) and an increase in PAH bioavailability. Organic-matter oxidation mobilized nutrients from the soil matrix. The bacterial populations were affected negatively, with a marked diminution in the diversity indices. In this combined treatment with oxidation and bioremediation working in tandem, the aliphatic-hydrocarbon fractions were largely eliminated along with additional PAHs. The chemical and spectroscopic analyses indicated a change in soil nutrients. In spite of the high residual-sulfate concentration, a rapid recovery of the cultivable bacterial population and the establishment of a diverse and equitable microbial community were obtained. Pyrosequencing analysis demonstrated a marked succession throughout this twofold intervention in accordance with the chemical and biologic shifts observed. These remediation steps produced different effects on the soil physiology. Spectroscopic analysis became a useful tool for following and comparing those treatments, which involved acute changes in a matrix of such chronically hydrocarbon-contaminated soil. The combined treatment increased the elimination efficiency of both the aliphatic hydrocarbons and the PAHs at the expense of the mobilized organic matter, thus sustaining the recovery of the resilient populations throughout the treatment. The high-throughput–DNA-sequencing techniques enabled the identification of the predominant populations that were associated with the changes observed during the treatments. [ABSTRACT FROM AUTHOR]

Soil microbial fuel cells (MFCs) are a sustainable technology that degrades organic pollutants while generating electricity. However, there have been no detailed studies of the mechanisms of pollutant degradation in soil MFCs. In this study, the effects of external resistance and electrode effectiveness on atrazine and hexachlorobenzene (HCB) degradation were evaluated, the performance of soil MFCs in the degradation of these pollutants under different soil redox conditions was assessed, and the associated microorganisms in the anode were investigated. With an external resistance of 20 Ω, the degradation efficiencies of atrazine and HCB were 95% and 78%, respectively. The degradation efficiency, degradation rate increased with decreasing external resistance, while the half-life decreased. There were different degradation trends for different pollutants under different soil redox conditions. The fastest degradation rate of atrazine was in the upper MFC section (aerobic), whereas that of HCB was in the lower MFC section (anaerobic). The results showed that electrode effectiveness played a significant role in pollution degradation. In addition, the microbial community analysis demonstrated that Proteobacteria, especially Deltaproteobacteria involved in current generation was extremely abundant (27.49%) on soil MFC anodes, although the percentage abundances of atrazine degrading Rhodocyclaceae (8.77%), Desulfitobacterium (0.64%), and HCB degrading Desulfuromonas (0.73%), were considerably lower. The results of the study suggested that soil MFCs can enhance the degradation of atrazine and HCB, and bioelectrochemical reduction was the main mechanism for the pollutants degradation. [ABSTRACT FROM AUTHOR]

Pollution in urban environments has raised concerns about the consumer safety of food produced by urban horticulture. Could a solid by-product of drinking water treatment provide the answer? Soil amendment with drinking water treatment residuals (DWTRs) has been shown to limit the uptake of metal contaminants, effectively immobilizing these elements within the soil; however, DWTRs possess a strong specific affinity for P and soil amendment with DWTRs can reduce P availability, thereby inducing plant P deficiencies and restricting growth. We conducted a glasshouse pot experiment to investigate the effect of alum-based DWTR amendment rate and P fertilizer placement method on Brassica pekinensis growth and As, Cd and P uptake under controlled conditions. Amendment of sandy loam soil A with 2–4 wt% DWTRs significantly (p < 0.001) reduced the Cd content of B. pekinensis tissues relative to untreated controls, with no significant difference in the P content of B. pekinensis tissues. Across all DWTR application rates examined (2–6 wt%), banded P fertilizer application resulted in 30–47% greater aboveground tissue P concentration compared to broadcast P fertilizer treatments (p < 0.05). Both the As and Cd content of B. pekinensis tissues were significantly (p < 0.001) reduced following 2–6 wt% amendment of sandy loam B with DWTRs. Results showed that a DWTR amendment rate of 2 wt% coupled with banded P fertilizer application resulted in the greatest B. pekinensis aboveground tissue biomass, along with a reduction in plant tissue Cd or As concentrations not significantly different from higher rates of DWTR amendment. Tissue P concentrations of B. pekinensis grown in soils amended with 2 wt% DWTRs were adequate for uninhibited plant growth. The use of DWTRs as an amendment to urban horticultural soils may provide a low-cost means of immobilizing trace metals without limiting plant uptake of applied fertilizer P. Additional study is required to quantify trace element release from DWTR-amended soils as a function of soil oxidation-reduction status. [ABSTRACT FROM AUTHOR]

Soddy-podzolic soils are widely distributed in European Russia, but their role as a sink for atmospheric methane is poorly documented and there is no information on the methanotroph diversity. We analysed the potential CH 4 -oxidation rates in soil samples and showed that the rate was significantly higher in forest soil than in arable soil, 1.21 and 0.40 ng CH 4 g soil −1 day −1 , respectively. PCR-DGGE and clone library analysis indicated the distinct methanotrophic communities in these soils. The pmoA sequences associated with uncultured soil methanotrophs, referred to as NUSC, dominated forest soil, while in agricultural soil, type I ( Methylobacter, Methylocaldum ) and type II ( Methylocystis, Methylosinus ) methanotrophs were dominant. A newly developed primer set was applied in qPCR analysis and revealed that the copy number of pmoA genes of NUSC methanotrophs in forest soil was (9.2 ± 0.87) × 10 4 g soil −1 , whereas the transcript number was (1.33 ± 0.31) × 10 6 g soil −1 . We concluded that differences between the CH 4 oxidation rates between forest and agriculture soils were driven by the structure of the methane-oxidizing community and that a novel group of methanotrophs may be an active participant in this process. [ABSTRACT FROM AUTHOR]

Unless properly managed, acid sulphate soils can exert a range of negative environmental impacts, including soil acidification and mobilization of metals and metalloids. Incorporation of organic matter in the form of plant mulches can substantially neutralize sulphuric soils and prevent the oxidation of sulphidic soils. These positive effects of dead plants are largely mediated by bacterial reduction of sulphates to sulphides, using the organic matter as a microbial nutrient source. However, very little is known about the effects of live plants on acid sulphate soils. In this study, we compared pH, Eh and sulphate content of sulphidic and sulphuric soils that were not planted (i.e. unplanted) with those soils planted with the following three common wetland plants: Phragmites, Melaleuca and Typha. Each of these plants is capable of growth in aerobic and flooded soils. In all our experiments, the presence of plants correlated with an increase in soil acidification rather than neutralizing soil acidity when compared to unplanted controls. The mechanism for this appears to be transport of oxygen down the soil profile by aerenchymatous tissue formed in these species, and the release of oxygen into the rhizosphere. [ABSTRACT FROM AUTHOR]

Thermal treatments prior or during chemical oxidation of aged polycyclic aromatic hydrocarbon (PAH)-contaminated soils have already shown their ability to increase oxidation effectiveness. However, they were never compared on the same soil. Furthermore, oxygenated polycyclic aromatic hydrocarbons (O-PACs), by-products of PAH oxidation which may be more toxic and mobile than the parent PAHs, were very little monitored. In this study, two aged PAH-contaminated soils were heated prior (60 or 90 °C under Ar for 1 week) or during oxidation (60 °C for 1 week) with permanganate and persulfate, and 11 O-PACs were monitored in addition to the 16 US Environmental Protection Agency (US EPA) PAHs. Oxidant doses were based on the stoichiometric oxidant demand of the extractable organic fraction of soils by using organic solvents, which is more representative of the actual contamination than only the 16 US EPA PAHs. Higher temperatures actually resulted in more pollutant degradation. Two treatments were about three times more effective than the others: soil heating to 60 °C during persulfate oxidation and soil preheating to 90 °C followed by permanganate oxidation. The results of this study showed that persulfate effectiveness was largely due to its thermal activation, whereas permanganate was more sensitive to PAH availability than persulfate. The technical feasibility of these two treatments will soon be field-tested in the unsaturated zone of one of the studied aged PAH-contaminated soils. [ABSTRACT FROM AUTHOR]

O 2 and CO 2 , the two essential reactants in weathering along with water and minerals, are important in deep regolith development because they diffuse to weathering fronts at depth. We monitored the dynamics of these gas concentrations in the hand-augerable zone on three ridgetops—one on granite and two on diabase—in Virginia (VA) and Pennsylvania (PA), U.S.A. and related the gas chemistry to regolith development. The VA granite and the PA diabase protoliths were more deeply weathered than the VA diabase. We attribute this to high protolith fracture density. The pO 2 and pCO 2 measurements of these more fractured sites displayed the characteristics of aerobic respiration year round. In contrast, the relation of pO 2 versus pCO 2 on the more massive VA diabase is consistent with seasonal changes in the dominant electron acceptor from O 2 to Fe(III), likely regulated by the expansion/contraction of nontronite in the soil BC horizon. These observations suggest that the fracture density is a first order control on deep regolith gas chemistry. However, fractures can be present in protolith but also can be caused by oxidation of ferrous minerals. We propose that subsurface pO 2 and weathering-induced fracturing can create positive feedbacks in some lithologies that cause regolith to thicken while nonetheless maintaining aerobic respiration at depth. In contrast, in the absence of weathering-induced fracturing and depletion of pO 2 , a negative feedback that may be modulated by soil micro-biota ultimately results in thin regolith. These feedbacks may have been important in weathering systems over much of earth's history. [ABSTRACT FROM AUTHOR]

Acid sulfate soil (ASS) is sensitive to redox fluctuations induced by climate change and human activities. Oxidation of sulfur and sulfide in ASS leads to the release of acid and consequently metals, posing severe hazards to coastal environment, while microbial contribution and response to oxidation is poorly understood. Here we used metagenomic sequencing to delineate the shift in microbial community structures and functional genes in ASS upon exposure to aerobic conditions. Aerobic incubation resulted in significant shifts in microbial communities in both topsoil and parent material. Archaea decreased significantly in the parent material after aerobic incubation. The relative abundance of sulfur cycling genes in the parent material layer was significantly higher than those in the topsoil, and multiple sulfide oxidation genes increased after aerobic oxidation. Metagenomic assembly enabled construction of eight key draft genomes from ASS. Three of them (GS3, GS6 and GT3) are novel strains of Thermoplasmatales , Acidothermales ( Acidothermus ) and Acidimicrobiales , respectively. Functional gene annotation of these population genomes revealed a dominance of sulfur cycling genes and acid tolerant genes. These findings highlight the microbial response to environmental change and identify the ecological adaptation and survival strategies of microbial communities in acid sulfate soils. [ABSTRACT FROM AUTHOR]

Decabromodiphenyl ether (BDE209) poses a significant threat to human health. Most research so far has focused on BDE209 debromination by the reduction, which will produce more toxic products and further cause more serious environmental problems. In this study, we focused on thermally activated persulfate oxidation of BDE209. Various factors have been investigated, such as initial persulfate (0.05, 0.1, 0.2 and 0.5 M) or BDE209 content, temperature, pH and inorganic ion. The results show the of BDE209 removal rate constants ( k 1 ) indicated quadratic curve relationship with initial persulfate concentrations ( k 1 = −0.293 × [PS] 0 2 + 0.267×[PS] 0 + 0.046, R 2 = 0.917, [PS] 0 = 0.05–0.5 M) and a good linear relationship with initial BDE209 contents ( k 1 = −0.004 × [BDE209] 0 + 0.312, R 2 = 0.994). At the test pH range of 3–9, the highest degradation efficiency occurred at pH 5. However, inhibitory effects were observed in the presence of bicarbonate (HCO 3 − ), and chloride (Cl − ) exhibited either positive or inhibitive effect on the BDE209 degradation. The addition of an appropriate level of Cl − (e.g., [Cl − ] 0 /[PS] 0 = 0.1/1) could significantly enhance the BDE209 decomposition, while higher contents of Cl − (e.g., [Cl − ] 0 /[PS] 0 = 2/1) resulted in totally inhibitory effect. [ABSTRACT FROM AUTHOR]

The long-term impact of biochar on soil properties and agronomic outcomes is influenced by changes in the physical and chemical properties of biochars that occur with time (aging) in soil environments. Fresh biochars, however, are often used in studies because aged biochars are generally unavailable. Therefore, a need exists to develop a method for rapid aging of biochars in the laboratory. The objectives of this study were to compare the physicochemical properties of fresh, laboratory-aged (LA), and field-aged (FA) (≥3 yr) biochars and to assess the appropriateness of a laboratory aging procedure that combines acidification, oxidation, and incubations as a mimic to field aging in neutral or acidic soil environments. Twenty-two biochars produced by fast and slow pyrolysis, and gasification techniques from five different biomass feedstocks (hardwood, corn stover, soybean stover, macadamia nut shells, and switchgrass) were studied. In general, both laboratory and field aging caused similar increases in ash-free volatile matter (% w/w), cation and anion exchange capacities, specific surface area, and modifications in oxygen-containing surface functional groups of the biochars. However, ash content increased for FA (18-195%) and decreased for LA (22-74%) biochars, and pH decreased to a greater extent for LA (2.8-6.7 units) than for FA (1.6-3.8 units) biochars. The results demonstrate that the proposed laboratory aging procedure is effective for predicting the direction of changes in biochar properties on field aging. However, in the future we recommend using a less aggressive acid treatment. [ABSTRACT FROM AUTHOR]

Villarrica (Chile) is a basaltic stratovolcano, currently in an open-conduit condition. It now has relatively frequent Strombolian and effusive eruptions, but it had large explosive eruptions in prehistoric times. Among them, the most recent eruption was Chaimilla, which occurred about 3100 years ago and produced deposits that indicate complex, multiphase eruptive dynamics. Significant differences in mineralogy and glass compositions of the erupted scoria suggest the eruption was fed by two distinct magma batches with similar bulk compositions but distinct crystallization and degassing histories. The lower sequence scoria has a complex crystal assemblage with several crystal populations produced by mixing between a relatively degassed magma containing Fo olivine, normally or reversely zoned plagioclase (An) and augite (type 1 magma), and a subordinate volume of more-primitive and more volatile-rich magma rising from depth (type 2 magma) and carrying normally zoned plagioclase and higher-Mg (Fo) olivine crystals. Type 2 magma was the main component emitted during the larger and more explosive eruptive phase that deposited the upper sequence. The Chaimilla eruption occurred under closed-vent conditions and was fed by water-rich magmas. When compared with the petrological features of the magma currently erupted at Villarrica, which has slightly more-evolved bulk compositions, lower crystal content and lower water content, these results suggest that the evolution in eruptive style of the volcano from highly explosive to a lava lake/Strombolian activity corresponds to significant changes in the shallow plumbing system (which is now at much shallower depths); these plumbing-system changes were not associated with significant changes in the parental magma compositions. [ABSTRACT FROM AUTHOR]

The potential effects of persulfate in situ chemical oxidation (ISCO) on metals and on long-term groundwater quality is an important issue because of the potential risks to public health and to the environment. Application of persulfate and its activation amendments to soil and groundwater can lead to complex interactions, altering geochemical conditions and processes, thereby affecting metals mobility. The mobility of cadmium sorbed on three soils varying in physical-chemical properties was investigated after chemical oxidation by unactivated and activated persulfate using mixed batch reactors. Each of the three soils was treated with two different concentrations of persulfate, 2.1 mM and 42 mM, and different activation amendments that included Fe(II), Fe(II)-EDTA, and high pH. Resulting solutions were analyzed for soluble cadmium after 48 h and 6 months. Results show that cadmium mobilization varied with the persulfate activation method and the soil type. The maximum amount of cadmium was mobilized with Fe(II)-EDTA activation and the least amount of cadmium was mobilized with high pH activation. In addition to Fe(II)-EDTA activation, cadmium was more mobile in soil with low soil organic carbon and low mineral content. Enhanced cadmium desorption at low pH and formation of soluble cadmium-EDTA complexes are the main mechanisms of cadmium mobilization from soils with persulfate ISCO. [ABSTRACT FROM AUTHOR]

The integrated effects of environmental factors on soil nitrification are largely unknown. Here, we performed a microcosm experiment to investigate the interactive effects of pH and NH 4 + on nitrification activity in two acidic soils with different land use patterns (Anhui soil, a forest soil; Jiangxi soil, a brush land soil). Both soils were incubated under native pH and CaCO 3 -manipulated pH in the presence or absence of added ammonium for 60 days. The addition of CaCO 3 alone did not change the nitrification activity of either soil. Ammonium addition stimulated nitrification in Anhui soil, but not in Jiangxi soil, and this stimulation was more pronounced with increased CaCO 3 . The ammonia monooxygenase ( amoA ) gene copy number of both ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) was much higher in Anhui soil than in Jiangxi soil. The amoA gene copy number of AOB in Anhui soil was more highly upregulated under CaCO 3 + NH 4 + than NH 4 + during incubation. In Anhui soil, changes in the denaturing gradient gel electrophoresis (DGGE) fingerprint patterns of bacterial amoA genes were parallel to changes in the amoA gene copy number of AOB. In Jiangxi soil, DGGE could not be performed because the PCR for bacterial DGGE did not yield any products, while quantitative PCR revealed that the amoA gene copy number of AOB changed during incubation. These results suggest that AOB plays an important role in CaCO 3 -enhanced nitrification of Anhui soil with ammonium addition. The low nitrification rates of Jiangxi soil regardless of CaCO 3 with or without NH 4 + supply may be ascribed to the lower activity of both AOB and AOA, especially AOA. [ABSTRACT FROM AUTHOR]

The impact of goethite on air-oxidation of PAH-contaminated soils was studied through two sets of experiments. (i) Soil extractable organic matter (EOM) and (ii) whole coking plant soils were oxidized at 60 and 100 °C for 160 d, with/without goethite. Organic matter (OM) mineralization was monitored via CO 2 production and polycyclic aromatic compounds (PACs) oxidation was investigated by GC–MS analyses. The decrease in EOM and PAH contents, and the oxygenated-PAC production observed during EOM oxidation, were enhanced by the presence of goethite. PACs were likely transformed at the goethite surface through electron transfer process. Mass carbon balance revealed a transfer from EOM to the insoluble organic fraction indicating condensation/polymerization of organics. Soil oxidation induced a decrease in EOM, PAH but also in oxygenated-PAC contents, underscoring different oxidation or polymerization behavior in soil. The goethite addition had a lesser impact suggesting that indigenous minerals played an important role in PAC oxidation. [ABSTRACT FROM AUTHOR]

Dormant season inorganic nitrogen (N) leaching varies considerably among forested catchments with similar bedrock, forest cover and deposition history. Recent work has highlighted the importance of winter rain-on-snow (ROS) events as a source of winter nitrate (NO-N) export, but differences among streams are likely due to differences in baseflow NO-N concentrations, and thus soil N processes. The objective of this study was to investigate rates of N-mineralization and nitrification as well as their potential environmental controls throughout the year, but with particular focus on the winter season in south-central Ontario, Canada. Field incubations were utilized to assess differences in NO-N and ammonium production over time and across topographic positions in two catchments with contrasting patterns of N export. Rates of nitrification were similar to rates of total mineralization, and nitrification rates were significantly higher during the summer and spring compared with the winter and fall; however, winter nitrification was substantial, and ranged from 19 to 36 % of annual rates. Seasonal differences in nitrification were largely driven by temperature, soil moisture and inorganic N concentration in soil. Rain and melting snow infiltrated the soil during ROS events, which were associated with increased NO-N availability, particularly in well-drained soils, and ROS-induced increases in stream nitrate concentrations were largest at the catchment dominated by well-drained soil. Annual nitrification fluxes were almost two orders of magnitude greater than N deposition or NO-N leaching fluxes at either catchment. Similar rates of NO-N production within the two catchments suggest that consumption of NO-N within wet soils is responsible for the 10-fold difference in NO-N export between the two streams. Notably, these results suggest that consumption processes were important for reducing NO-N export even during winter ROS events. [ABSTRACT FROM AUTHOR]

Highlights: [•] We investigated CH4 oxidation in an afforested chronosequence in Denmark. [•] We linked CH4 oxidation with the abundance of methane oxidizing bacteria (MOB). [•] CH4 oxidation increased with time since afforestation. [•] The abundance of MOB also increased following afforestation. [•] Changes in soil organic carbon and bulk density were the main drivers. [ABSTRACT FROM AUTHOR]

Highlights: [•] Increasing nutrient loads and soil pH selected distinct groups of AOA and AOB. [•] AOB was the most abundant and diverse group in highly impacted areas. [•] Changes on AOB community structure were mainly driven by ammonium concentrations. [•] AOA was dominant in less impacted areas and reacted to changes on pH and nitrogen. [ABSTRACT FROM AUTHOR]

Abstract: In periodically flooded soils, interactions of Cu with biogenic sulfide formed during soil reduction lead to the precipitation of sparingly soluble Cu-sulfides. In contaminated soils, however, the amounts of Cu can exceed the amount of sulfate available for microbial reduction to sulfide. In laboratory batch experiments, we incubated a paddy soil spiked to ∼4.4mmolkg-1 (280mgkg−1) Cu(II) to monitor temporal changes in the concentrations of dissolved Cu and the speciation of solid-phase Cu during 40days of soil reduction and 28days of reoxidation as a function of initially available reducible sulfate (0.06, 2.09 or 5.92mmolkg−1). Using Cu K-edge EXAFS spectroscopy, we found that a large fraction of Cu(II) became rapidly reduced to Cu(I) (23–39%) and Cu(0) (7–17%) before the onset of sulfate reduction. Combination with results from sequential Cu extraction and chromium reducible sulfur (CRS) data suggested that complexation of Cu(I) by reduced organic S groups (Sorg) may be an important process during this early stage. In sulfate-depleted soil, Cu(0) and Cu(I)–Sorg remained the dominant species over the entire reduction period, whereas in soils with sufficient sulfate, initially formed Cu(0) and (remaining) Cu(II) became transformed into Cu-sulfide during continuing sulfate reduction. The formation of Cu(0), Cu(I)–Sorg, and Cu-sulfide led to an effective decrease in dissolved Cu concentrations. Differences in Cu speciation at the end of soil reduction however affected the dynamics of Cu during reoxidation. Whereas Cu(0) was rapidly oxidized to Cu(II), more than half of the S-coordinated Cu fraction persisted over 14days of aeration. Our results show that precipitation of Cu(0) and complexation of Cu(I) by reduced organic S groups are important processes in periodically flooded soils if sulfide formation is limited by the amount of available sulfate or the duration of soil flooding. The speciation changes of Cu described in this study may also affect the speciation and solubility of other chalcophile metals in redox-dynamic wetland soils. [Copyright &y& Elsevier]

Soil manganese oxides are highly reactive and can strongly influence soil chemical transformations even when present in relatively minor concentrations. The continued reactivity of these oxides is dependent on regeneration, yet the mechanisms of Mn(II) oxidation in soils are not completely understood. We examined oxidation of added Mn(II) in four soils with a reducible Mn content ranging from 9.1 to 319 mmol kg-1 (0.05-1.75%). The Mn in these soils was concentrated in manganiferous oxide coatings or concretions ~50-100 µm in diameter. The progress of oxidation of Mn(II) was measured by both Mn K-edge XANES spectroscopy and the ability of the soil to oxidize added Cr(III)Cl3 to Cr(VI) (Standard Net Cr Oxidation Test). Addition of Mn(II) to a soil sample caused an initial decrease in the energy position of the main absorption edge in XANES spectra collected from areas of high Mn concentration, showing sorption of the added Mn(II). Repeated scans over 30-50 h showed movement of the main edge to a higher energy, close to that of the soil before treatment, demonstrating oxidation. Chromium oxidation initially decreased due to blockage of reactive sites by sorbed Mn(II). It then increased linearly over the same time period to values higher than the untreated soil, confirming the oxidation of the added Mn(II) and an increase in overall Mn oxide reactive sites. Oxidation continued even after exposure to strongly ionizing X-rays, suggesting a coupled biotic/abiotic pathway. [ABSTRACT FROM AUTHOR]

The 14C contents and the carbon ( C) pool sizes for Rothamsted Carbon ( RothC) model pools and soil fractions determined by physical separation and subsequent chemical oxidation were directly compared for an agricultural topsoil ( Dystric Cambisol) from a long-term experimental field in central Japan. The RothC model was run from 1975 to 2009 and the C concentration and Δ14C value of each pool and for the bulk soil were compared with the physical fractions that have been, according to literature, suggested as corresponding with model pools. When compared with the default estimate of the inert organic matter ( IOM) pool size derived from an exponential dependency on total organic carbon ( TOC), direct estimation of IOM pool size determined from the C remaining after chemical oxidation of the silt plus clay (< 63 µm) fraction improved the model performance for TOC changes over the 34-year experimental period. The size of each model pool matched that of the physical fractions well, whereas the Δ14C values clearly differed between modelled pools and corresponding physical fractions. The physical fractions showed more negative Δ14C values with 50-190‰ (indicating slower turnover rates) compared with the active pools in RothC, whereas using the oxidation residue generated more positive Δ14C values with 700‰ (faster turnover) than the original RothC IOM pool. These results suggest that (i) the proposed physical fractionation scheme improves the model performance in simulating TOC changes at the temporal scale of decades under the current climate and (ii) long-term predictions should be interpreted carefully because of the large discrepancy in 14C-based turnover rate between the physical fractions and RothC model pools. [ABSTRACT FROM AUTHOR]

Nitrous oxide ( N2O) is emitted to the atmosphere as a by-product of nitrification and denitrification by soil microbial processes. Differences in climate, soil and management regulate these processes, causing N2O emissions to vary in space and time. This study aimed to identify and rank the soil properties that control N2O emissions in non-tilled soils under different crops. Over a period of 2 years, gas samples were taken from closed chambers and soil properties were determined once per season. N2O emission rates were highly variable (from −15 to 314 µg N2O-N m−2 hour−1). A regression tree analysis allowed us to classify soil N2O emissions into three groups, separated by topsoil temperature (primary factor) and water-filled pore space ( WFPS, secondary factor). N2O emissions were small (mean 4.22 µg N2O-N m−2 hour−1) with topsoil temperature less than 14°C (Group 1), large (mean 61.87 µg N2O-N m−2 hour−1) with topsoil temperature between 14 and 23°C and WFPS more than 58.5% (Group 2) and moderate (mean 21.4 µg N2O-N m−2 hour−1) with topsoil temperature more than 23°C and WFPS less than 58.5% (Group 3). These emission groups allow for more efficient sampling of N2O emissions in the field: in winter, when topsoil temperatures are less than 14°C and N2O emissions are expected to be small or even negligible, sampling frequency can be reduced; in autumn and spring, when topsoil temperatures are more than 14°C and WFPS is more than 60-70%, sampling frequency should be increased. [ABSTRACT FROM AUTHOR]

Selenium ( Se) is an essential trace element for animals and displays a narrow range between dietary deficiency and toxicity. The toxicity of Se depends on its bioavailability, which is directly related to its oxidation states, of which four occur in the environment ( SeVI, SeIV, Se0 and SeII−). Microbial communities drive the cycling of Se between these oxidation states. In order to investigate the effect of microbial activity on Se cycling in the environment, a field site in County Meath, Ireland, was identified with anomalously large concentrations of Se as a result of weathering of black shales within the Lucan formation, leading to cases of Se toxicity in farm animals. Soil cores were extracted from the site for Se speciation and microbial community analysis prior to microcosm experiments to assess Se stability and microbial Se transformations. Selenium was present as a recalcitrant, reduced organic phase that was strongly coordinated with carbon, concordant with suggested hypotheses of Se phyto-concentration within a clay-lined, postglacial marshland. Selenium was not mobilized in microcosm experiments, and supplementation with SeVI resulted in rapid reduction and removal from solution as Se0. Additional electron donors did not affect Se stability or removal from solution, although nitrate did hinder SeVI reduction. Terminal restriction fragment length polymorphism analysis indicated a significant shift in microbial community after amendment with SeVI. This work extends the current knowledge of Se cycling in the environment, and provides information on the bioavailability of Se in the soil, which determines Se content of foodstuffs. [ABSTRACT FROM AUTHOR]

Aims and Methods Vascular plants are known to influence the production, transport and oxidation of methane in wetland soils, but these processes are not well understood. Using plants grown in intact peat cores, we compared the influence upon methane emissions of 20 forb and graminoid species from European wetlands. We measured plant-mediated transport of methane (conduit or chimney effect) using a novel agar-sealing technique that prevented methane exchange from the bare soil to the atmosphere. Important Findings The plant-mediated transport (chimney effect) represented between 30% and almost 100% of the total methane flux, with graminoids exhibiting greater internal transport than forbs. In general, plants with less dense root tissues and a relatively larger root volume exhibited a larger chimney effect. Most species (12 out of 20) significantly reduced methane emissions compared to bare soil and only one species, Succisa pratensis, increased them. We suggest that characterising vegetation in terms of plant functional traits and plant processes offers an effective method for estimating methane emissions from wetlands. However, we found no correlation between the magnitude of the chimney effect and the overall influence of different plant species on methane emissions. Besides introducing a useful tool to study plant-mediated transport, this work suggests that characterising vegetation in terms of functional traits could improve estimates of methane emissions from wetlands, which in turn could help in designing mitigation strategies. [ABSTRACT FROM PUBLISHER]

Background and aims: We studied the response of lignin oxidation in soils of a beech/oak forest to changes in litter fall. Additionally we considered possible factors in lignin oxidation, including altered (i) input of fresh organic matter and (ii) fungi-to-bacteria ratios. Methods: The field-based experiment included (i) doubling and (ii) exclusion of litter fall and (iii) controls with ambient litter fall. Soil (0-20 cm depth) was sampled after 8 years. We analyzed (i) lignin using the CuO oxidation method, (ii) stocks of free and mineral-bound organic carbon (OC), (iii) the response of soil organic matter (SOM) decomposition to addition of labile organic compounds in laboratory incubations, and (iv) ratios of fungal- vs. bacterial-derived amino sugars (F/B ratios). Results: Litter exclusion increased stocks of free-light fraction OC, F/B ratios, the ability of the microbial community to use labile compounds for SOM decomposition, as well as acid-to-aldehyde ratios of vanillyl-type lignin phenols in A horizons. Litter addition had no such effects. We assume that litter exclusion caused enhanced transport of organic debris from lower forest floor horizons with rainwater into the A horizon. Enhanced input of organic debris might have increased (i) the availability of labile compounds and (ii) F/B ratios. Consequently, lignin oxidation increased. Conclusions: Enhanced input of organic debris from forest floors can increase lignin oxidation in mineral topsoils of the studied forest. The expected gradual changes in litter fall due to climate change likely will cause no such effects. [ABSTRACT FROM AUTHOR]

Permafrost-affected tundra soils are significant sources of the climate-relevant trace gas methane (CH4). The observed accelerated warming of the arctic will cause deeper permafrost thawing, followed by increased carbon mineralization and CH4 formation in water-saturated tundra soils, thus creating a positive feedback to climate change. Aerobic CH4 oxidation is regarded as the key process reducing CH4 emissions from wetlands, but quantification of turnover rates has remained difficult so far. The application of carbon stable isotope fractionation enables the in situ quantification of CH4 oxidation efficiency in arctic wetland soils. The aim of the current study is to quantify CH4 oxidation efficiency in perma-frost-affected tundra soils in Russia's Lena River delta based on stable isotope signatures of CH4. Therefore, depth profiles of CH4 concentrations and δCH4 signatures were measured and the fractionation factors for the processes of oxidation (αox) and diffusion (αdiff) were determined. Most previous studies employing stable isotope fractionation for the quantification of CH4 oxidation in soils of other habitats (such as landfill cover soils) have assumed a gas transport dominated by advection (αtrans = 1). In tundra soils, however, diffusion is the main gas transport mechanism and diffusive stable isotope fractionation should be considered alongside oxidative fractionation. For the first time, the stable isotope fractionation of CH4 diffusion through water-saturated soils was determined with an diff = 1.001 ± 0.000 (n = 3). CH4 stable isotope fractionation during diffusion through air-filled pores of the investigated polygonal tundra soils was αdiff 1.013 ±0.003 (n = 18). Furthermore, it was found that αox differs widely between sites and horizons (mean αox = 1.017 ± 0.009) and needs to be determined on a case by case basis. The impact of both fractionation factors on the quantification of CH4 oxidation was analyzed by considering both the potential diffusion rate under saturated and unsaturated conditions and potential oxidation rates. For a submerged, organic-rich soil, the data indicate a CH4 oxidation efficiency of 50 % at the anaerobic-aerobic interface in the upper horizon. The improved in situ quantification of CH4 oxidation in wetlands enables a better assessment of current and potential CH4 sources and sinks in permafrost-affected ecosystems and their potential strengths in response to global warming. [ABSTRACT FROM AUTHOR]

Background: Oxidation-reduction and acid-base reactions are essential for the maintenance of all living organisms. However, redox potential (Eh) has received little attention in agronomy, unlike pH, which is regarded as a master variable. Agronomists are probably depriving themselves of a key factor in crop and soil science which could be a useful integrative tool. Scope: This paper reviews the existing literature on Eh in various disciplines connected to agronomy, whether associated or not with pH, and then integrates this knowledge within a composite framework. Conclusions: This transdisciplinary review offers evidence that Eh and pH are respectively and jointly major drivers of soil/plant/microorganism systems. Information on the roles of Eh and pH in plant and microorganism physiology and in soil genesis converges to form an operational framework for further studies of soil/plant/microorganism functioning. This framework is based on the hypothesis that plants physiologically function within a specific internal Eh-pH range and that, along with microorganisms, they alter Eh and pH in the rhizosphere to ensure homeostasis at the cell level. This new perspective could help in bridging several disciplines related to agronomy, and across micro and macro-scales. It should help to improve cropping systems design and management, in conventional, organic, and conservation agriculture. [ABSTRACT FROM AUTHOR]

Abstract: To realistically understand spatial and temporal variations in the net ecosystem production (NEP) of rice paddies in Japan, we enhanced the existing diagnostic-type biosphere model with the addition of agricultural processes. Validated with a comparison of seasonal and annual variations over 5 years, the NEP estimations bore good agreement with the measurements. In regional-scale analyses, we targeted all rice paddy fields in Japan from January 2001 to December 2009. Before and after the model enhancement, the NEP showed very different spatial variations and absolute values, suggesting that the most effective improvements were the introduction of harvest and soil oxidation–reduction processes. In annual anomaly analyses covering a 9-year period, the NEP was found to be negative in 2003 and 2006 (−0.11 and −0.25TgC/year) and positive in 2004 and 2007 (+0.02 and +0.21TgC/year). We found that the negative values were caused by decreases in solar radiation and air temperature and the positive values were caused by increases in these two parameters and precipitation. In response to the NEP, our obtained harvested grain biomass values in 2003 and 2006 were lower than usual. The results were in good agreement with the results from reports of the Japan Meteorological Agency and the Ministry of Agriculture, Forestry, and Fisheries. [Copyright &y& Elsevier]

The potential and feasibility of treating soil contaminated with electrical insulating oil, Aroclor 1016, containing polychlorinated biphenyls (PCBs) with stabilized hydrogen peroxide were evaluated using columns packed with soils of two different matrixes. The column experiments showed that PCBs degraded by the stabilized hydrogen peroxide treatment in both soil matrixes, although the efficacy of the treatment depended strongly on the soil characteristics. The removal of PCB-containing oil was higher in sandy silt soil than in sandy soil. While a higher iron content promoted hydrogen peroxide oxidation of the contaminant in sandy silt soil, lower permeability and higher organic matter content contributed to an oxidation decrease as a function of depth. Dehydrogenase activity measurements indicated no substantial changes in microbial activity during the treatment of both sandy and sandy silt soils, thus offering opportunities to apply the hydrogen peroxide treatment to the remediation of PCB-contaminated soil. [ABSTRACT FROM PUBLISHER]

Abstract: Thirty very deep aquic spodosols in swales of the Bassendean Dune System, Western Australia were investigated for their potential to acidify due to their contents of acid-forming sulphur minerals. Pyrite commonly occurs in B, Bh, C and sometimes A and E horizons of these soils. Two morphologies of pyrite are present: single crystals of pyrite are euhedral cubic or octahedral (≤1μm) and framboidal pyrite aggregate grains range from 1 to 10μm. Elemental sulphur in the form of anhedral particles 10–500nm may occur in E, B and Bh horizons and is strongly associated with organic matter and jarosite sometimes occurred in the A horizon. Rare marcasite and mackinawite are other acid generating sulphide minerals and indicate the diverse redox and other chemical conditions that exist in these spodosols. Consequently drying and aeration of these soils due to drainage and possibly also to climate change acidifies both soil and groundwater. These spodosols are therefore acid sulphate soils. Acid buffering is mostly minor and is provided by organic matter and allophane. These observations of acid generating sulphides in spodosols may indicate that very acid nonaquic spodosols elsewhere were once saturated and contained pyrite before the profiles experienced permanent or episodic oxidising conditions. [Copyright &y& Elsevier]

Abstract: Soil science research has probably underestimated the significance that short-term, episodic cycles of reduction and oxidation has had on phosphorus (P) reactivity. Here, the effects of eleven pulsed reduction-oxidation (including wet-dry) cycles on soil P dynamics are compared for 12 soils having contrasting properties and all overfertilised with respect to P. The laboratory based incubation conditions attempted to simulate transient waterlogging of the soil profile and involved repeated sampling and analysis of both the solution and solid phase P forms. An initial increase in P concentration in solution that occurred up to and including the fourth full cycle was followed by a sharp decline in concentration for all but one soil. Accompanying changes in the main extractable forms of P, which appeared to be cumulative, could be summarised as a general decline in the organic P fraction and an overall increase in amorphous associated inorganic forms of P. The fact that up to 60% of the total soil P was demonstrated to change its sensitivity for a particular extractant suggests that these operationally defined P forms are susceptible to transformation as a consequence of changing environmental conditions. There was also a suggestion that certain of the changes in P forms were irreversible. While the laboratory conditions imposed do represent extreme conditions the soils only experienced cyclic changes in their moisture regime. If timing and frequency of intense precipitation events are likely to increase, as predicted in many climate change scenarios, then these results suggest that the effects of episodic redox pulses may have implications for P cycling in agricultural soils. [Copyright &y& Elsevier]

Abstract: A batch experiment was conducted to assess the impact of chemical oxidation using modified Fenton reaction on PAH content and on physico-chemical and biological parameters of an industrial PAH contaminated soil in unsaturated condition. Two levels of oxidant (H2O2, 6 and 65gkg−1) and FeSO4 were applied. Agronomic parameters, bacterial and fungal density, microbial activity, seed germination and ryegrass growth were assessed. Partial removal of PAHs (14% and 22%) was obtained with the addition of oxidant. The impact of chemical oxidation on PAH removal and soil physico-chemical and biological parameters differed depending on the level of reagent. The treatment with the highest concentration of oxidant decreased soil pH, cation exchange capacity and extractable phosphorus content. Bacterial, fungal, and PAH degrading bacteria densities were also lower in oxidized soil. However a rebound of microbial populations and an increased microbial activity in oxidized soil were measured after 5weeks of incubation. Plant growth on soil treated by the highest level of oxidant was negatively affected. [Copyright &y& Elsevier]

Landfill leachate is one of the most recalcitrant wastes for biotreatment and can be considered a potential source of contamination to surface and groundwater ecosystems. In the present study, Fenton oxidation was employed for degradation of stabilized landfill leachate. Response surface methodology was applied to analyze, model and optimize the process parameters, i.e. pH and reaction time as well as the initial concentrations of hydrogen peroxide and ferrous ion. Analysis of variance showed that good coefficients of determination were obtained (R2 > 0.99), thus ensuring satisfactory agreement of the second-order regression model with the experimental data. The results indicated that, pH and its quadratic effects were the main factors influencing Fenton oxidation. Furthermore, antagonistic effects between pH and other variables were observed. The optimum H2O2 concentration, Fe(II) concentration, pH and reaction time were 0.033 mol/L, 0.011 mol/L, 3 and 145 min, respectively, with 58.3% COD, 79.0% color and 82.1% iron removals. [ABSTRACT FROM AUTHOR]

Abstract: Bench-scale experiments were conducted to investigate the potassium permanganate demand, a key parameter for in situ chemical oxidation (ISCO) system design, and its variation with depth in PAHs-contaminated site of a coking plant. The concentrations of permanganate decreased rapidly during the first 8 d of the reaction process. The reaction follows first order kinetics, with rate constant ranging from 0.01 to 0.3/h. The total oxidant demand (TOD) is significantly higher for clayey silt fill than for soils of other lithology. The typical TOD is about 50g MnO4 −/kg soil for clayey silt fill, 20–40g MnO4 −/kg soil for silt, silty clay and 1–7g MnO4 −/kg soil for fine sand. Statistical analysis revealed that TOD was positively correlated with total organic carbon (TOC) content, clay content and PAHs concentrations, besides sand content, meanwhile TOC was the parameter with the strongest influence on oxidant demand. After 32 d duration of oxidation, PAHs in all tested soils were effectively removed, with total removal percent ranging from 78% to 99%, and small molecular weight PAHs were removed to a greater extent than high molecular weight PAHs. Parameters obtained in this study, combined with soil bulk density, soil porosity and soil moisture, can be used for full-scale ISCO system design and application in coking contaminated site. [Copyright &y& Elsevier]

DNA-based stable-isotope probing was applied to identify the active microorganisms involved in syntrophic butyrate oxidation in paddy field soil. After 14 and 21 days of incubation with [U-13C]butyrate, the bacterial Syntrophomonadaceae and the archaeal Methanosarcinaceae and Methanocellales incorporated substantial amounts of 13C label into their nucleic acids. Unexpectedly, members of the Planctomycetes and Chioroflexi were also labeled with 13C by yet-unclear mechanisms. [ABSTRACT FROM AUTHOR]

Abstract: In field studies, various workers have observed a stimulation of organic matter breakdown by visible light and UV radiation. We aimed to confirm the involvement of UV radiation under controlled laboratory conditions and quantify the magnitude of any stimulation. Grass and pine foliage samples were oven-dried and continuously exposed to UV radiation at room temperature for up to 60 days. A range of UV flux densities was established using shading to different levels. After UV exposure under air-dry conditions, samples were rewetted and incubated in the dark with microbial inoculums to investigate whether UV exposure had rendered samples more susceptible to subsequent microbial decomposition. However, we found no weight loss associated with different UV flux densities. The same finding held true for grass and pine litter samples. Similarly, microbial decomposition of either grass or pine litter was not enhanced by prior UV exposure. These findings suggest that UV-induced photooxidation of dry materials cannot be responsible for the observed apparent enhancement of weight loss of litter samples under UV exposure in the field. [Copyright &y& Elsevier]

Abstract: The effects of repeated synthetic fertilizer or cattle slurry applications at annual rates of 50, 100 or 200m3 ha−1 yr−1 over a 38 year period were investigated with respect to herbage yield, N uptake and gross soil N dynamics at a permanent grassland site. While synthetic fertilizer had a sustained and constant effect on herbage yield and N uptake, increasing cattle slurry application rates increased the herbage yield and N uptake linearly over the entire observation period. Cattle slurry applications, two and four times the recommended rate (50m3 ha−1 yr−1, 170kgNha−1), increased N uptake by 46 and 78%, respectively after 38 years. To explain the long-term effect, a 15N tracing study was carried out to identify the potential change in N dynamics under the various treatments. The analysis model evaluated process-specific rates, such as mineralization, from two organic-N pools, as well as nitrification from NH4 + and organic-N oxidation. Total mineralization was similar in all treatments. However, while in an unfertilized control treatment more than 90% of NH4 + production was related to mineralization of recalcitrant organic-N, a shift occurred toward a predominance of mineralization from labile organic-N in the cattle slurry treatments and this proportion increased with the increase in slurry application rate. Furthermore, the oxidation of recalcitrant organic-N shifted from a predominant NH4 + production in the control treatment, toward a predominant NO3 − production (heterotrophic nitrification) in the cattle slurry treatments. The concomitant increase in heterotrophic nitrification and NH4 + oxidation with increasing cattle slurry application rate was mainly responsible for the increase in net NO3 − production rate. Thus the increase in N uptake and herbage yield on the cattle slurry treatments could be related to NO3 − rather than NH4 + production. The 15N tracing study was successful in revealing process-specific changes in the N cycle in relationship to long-term repeated amendments. [Copyright &y& Elsevier]

Abstract: A novel type of planar optodes for simultaneous optical analysis of pH and oxygen dynamics in the rhizosphere is introduced. The combination of the optical, non-invasive measurement of these parameters with sterile sampling of rhizosphere solution across and along growing roots by use of a novel type of rhizobox provides a methodical step forward in the investigation of the physicochemical dynamics of the rhizosphere and its underlying matter fluxes between roots and soil. In this study, this rhizobox was used to investigate the effect of oxygen releasing roots of three Juncus species on the amount and distribution of organic acids in reductive, oxygen-deficient soils of different pH (pH 3.9–pH 5.9). Pronounced diurnal variations of oxygen concentration and pH along the roots, particularly along the elongation zone were observed. Long-term records over more than eight weeks revealed considerable spatial and temporal patterns of oxygen over a range of almost 200 μmol O2 L−1 and pH dynamics of ±1.4 pH units in the rhizosphere. A strong effect of oxidative acidification due to oxygen release by the plant roots was clearly visible for Juncus effusus, whereas the roots of Juncus articulatus alkalinized the rhizosphere. In contrast, roots of Juncus inflexus induced no effects on rhizospheric pH. Only four different organic acids (oxalate, acetate, formate and lactate) were detectable in all soil solutions. Maximal concentration of all organic acids occurred at pH 3.9, whereas the lowest concentration of each organic acid was found at pH 5.9. Hence, considering the pH-dependence of the redox potential, the acid soil provided increased reductive conditions leading to slower anaerobic degradation of organic acids to CO2 or methane (CH4). The concentration of organic acids decreased by up to 58% within a distance of only 4 mm from the bulk soil to the root surface, i.e. reciprocal to the pronounced O2-gradient. The decreasing presence of organic acids toward the oxygen releasing roots is possibly due to a change in the composition of the microbial community from anaerobic to aerobic conditions. The present study highlights the dynamic interplay between O2 concentration, pH and organic acids as key parameters of the physicochemical environment of the rhizosphere, particularly for wetland plants growing in oxygen-deficient waterlogged soils. [Copyright &y& Elsevier]

• Vascular wetland plants may substantially increase methane emissions by producing root exudates and easily degradable litter, and by providing a low resistance diffusion pathway via their aerenchyma. However, model studies have indicated that vascular plants can reduce methane emission when soil oxygen demand is exceeded by oxygen released from roots. Here, we tested whether these conditions occur in bogs dominated by cushion plants. • Root–methane interactions were studied by comparing methane emissions, stock and oxygen availability in depth profiles below lawns of either cushion plants or Sphagnum mosses in Patagonia. • Cushion plants, Astelia pumila and Donatia fascicularis, formed extensive root systems up to 120 cm in depth. The cold soil (< 10°C) and highly decomposed peat resulted in low microbial activity and oxygen consumption. In cushion plant lawns, high soil oxygen coincided with high root densities, but methane emissions were absent. In Sphagnum lawns, methane emissions were substantial. High methane concentrations were only found in soils without cushion plant roots. • This first methane study in Patagonian bog vegetation reveals lower emissions than expected. We conclude that cushion plants are capable of reducing methane emission on an ecosystem scale by thorough soil and methane oxidation. [ABSTRACT FROM AUTHOR]