Oxidation Of Soil Organic Matter Research Articles

Enhancing Soil Organic Matter Transformation through Sustainable Farming Practices: Evaluating Labile Soil Organic Matter Fraction Dynamics and Identifying Potential Early Indicators

The growing global population and increasing demand for agricultural products have exerted significant pressure on agricultural systems. As a result, soil organic matter depletion and degradation have become prevalent issues, including in regions such as South Bohemia, Czech Republic, where conventional farming practices are predominant. Soil organic matter (SOM) plays a critical role in soil health, crop productivity, and the sustainability of agricultural systems, with changes occurring in both the total and labile fractions of the organic matter pools. However, changes in the total soil organic matter carbon pool (TOC) resulting from agricultural practices occur gradually and may become evident only after several years, posing challenges for timely management adjustments. Therefore, the identification of early indicators of SOM dynamics is crucial for implementing prompt corrective actions. The aim of this study was to evaluate the effects of sustainable management practices, such as cultivated crops (Pisum sativum and Lupinus albus), selected entomopathogenic and myco parasitic fungi (MEHA) (Trichoderma virens and Metarhizium brunneum), and lactic acid bacteria (LAB) on the labile fraction of the SOM pool (CLSOM) and identify potential early indicators. Our findings demonstrated that the type of crop and applied microorganisms (treatments) significantly affected the CLSOM in peas, and the crop growth stages affected the TOC in both pea and lupin. Growth stages also showed an impact on the CLSOM in lupin. Moreover, in both crops, the change in CLSOM correlated with changes in the SOM oxidation rate constant (k), carbon lability index (LI), carbon management index (CMI), and carbon enrichment ratio (ER). Conversely, changes in the TOC did not exhibit significant correlations, except for LI and CMI, which showed a positive correlation with the TOC in peas (p < 0.05). Furthermore, the separate application of MEHA and LAB on seeds or leaves resulted in increased SOM carbon pools compared with the combined application. The application of these beneficial microorganisms in pea and lupin crops showed potential in maintaining or increasing CLSOM, which can be assessed early through indicators such as k, LI, CMI, and ER. Contributing to the development of sustainable soil management strategies, future research should further investigate different crops and microorganisms—and the mechanisms underlying their observed relationships—and explore additional early indicators to refine and optimize sustainable agricultural practices.

One thousand soils for molecular understanding of belowground carbon cycling

While significant progress has been made in understanding global carbon (C) cycling, the mechanisms regulating belowground C fluxes and storage are still uncertain. New molecular technologies have the power to elucidate these processes, yet we have no widespread standardized implementation of molecular techniques. To address this gap, we introduce the Molecular Observation Network (MONet), a decadal vision from the Environmental Molecular Sciences Laboratory (EMSL), to develop a national network for understanding the molecular composition, physical structure, and hydraulic and biological properties of soil and water. These data are essential for advancing the next generation of multiscale Earth systems models. In this paper, we discuss the 1000 Soils Pilot for MONet, including a description of standardized sampling materials and protocols and a use case to highlight the utility of molecular-level and microstructural measurements for assessing the impacts of wildfire on soil. While the 1000 Soils Pilot generated a plethora of data, we focus on assessments of soil organic matter (SOM) chemistry via Fourier-transform ion cyclotron resonance-mass spectrometry and microstructural properties via X-ray computed tomography to highlight the effects of recent fire history in forested ecosystems on belowground C cycling. We observed decreases in soil respiration, microbial biomass, and potential enzyme activity in soils with high frequency burns. Additionally, the nominal oxidation state of carbon in SOM increased with burn frequency in surface soils. This results in a quantifiable shift in the molecular signature of SOM and shows that wildfire may result in oxidation of SOM and structural changes to soil pore networks that persist into deeper soils.

Efficient oriented interfacial oxidation of petroleum hydrocarbons by functionalized Fe/N co-doped biochar-mediated heterogeneous Fenton for heavily contaminated soil remediation

In this study, a novel alkylbenzenized Fe/N co-doped biochar (ABD-Fe/N@BC) catalyst was successfully fabricated by sequential pyrolysis and hydrothermal methods. Compared with traditional heterogeneous Fenton catalysts, this catalyst presented a higher adsorptive and catalytic activity to alkanes (11689 mg/kg) and polycyclic aromatic hydrocarbons (PAHs: 8554 mg/kg) in two soil with different contents of soil organic matter (SOM) (S1:10.38%; S2: 4.14%). Therefore, macro-alkanes and PAHs could be simultaneously adsorbed on ABD-Fe/N@BC surface through hydrophobic and π-π interactions to form a highly efficient oriented interfacial oxidation system. As a result, the ABD-Fe/N@BC/H2O2 system exhibited the most effectiveness for total petroleum hydrocarbons (TPHs) removal with 18505.74 and 19610.55 mg/kg oxidation amounts in S1 and S2, equal to 91.42 and 96.88% oxidation efficiencies, respectively. Thus, the “adsorption - oxidation” mode contributed to settling the inhibitory effect of SOM on TPHs oxidation. By contrast, only 35.39 and 46.86% TPHs oxidation efficiencies were reached in the EDTA-Fe2+/H2O2 system, while the SOM oxidation efficiencies were up to 50.11 and 69.43% in S1 and S2, respectively, which was around 3.4-fold than that of ABD-Fe/N@BC/H2O2 system. Furthermore, compared to EDTA-Fe2+/H2O2 system, the ABD-Fe/N@BC/H2O2 system characterized stronger anti-interference ability to other coexisting substances. Additionally, the •OH formed on the surface of ABD-Fe/N@BC by activating H2O2 predominantly induced the oxidation of alkanes and PAHs. Besides, O2•− was another critical reactive oxygen species responsible for PAHs oxidation. This study provided a promising novel heterogeneous Fenton catalyst to efficiently remediate heavily multicomponent petroleum hydrocarbons contaminated soil, especially rich in SOM.

Soil carbon consequences of historic hydrologic impairment and recent restoration in coastal wetlands

Coastal wetlands provide key ecosystem services, including substantial long-term storage of atmospheric CO2 in soil organic carbon pools. This accumulation of soil organic matter is a vital component of elevation gain in coastal wetlands responding to sea-level rise. Anthropogenic activities that alter coastal wetland function through disruption of tidal exchange and wetland water levels are ubiquitous. This study assesses soil vertical accretion and organic carbon accretion across five coastal wetlands that experienced over a century of impounded hydrology, followed by restoration of tidal exchange 5 to 14 years prior to sampling. Nearby marshes that never experienced tidal impoundment served as controls with natural hydrology to assess the impact of impoundment and restoration. Dated soil cores indicate that elevation gain and carbon storage were suppressed 30–70 % during impoundment, accounting for the majority of elevation deficit between impacted and natural sites. Only one site had substantial subsidence, likely due to oxidation of soil organic matter. Vertical and carbon accretion gains were achieved at all restored sites, with carbon burial increasing from 96 ± 33 to 197 ± 64 g C m−2 y−1. The site with subsidence was able to accrete at double the rate (13 ± 5.6 mm y−1) of the natural complement, due predominantly to organic matter accumulation rather than mineral deposition, indicating these ecosystems are capable of large dynamic responses to restoration when conditions are optimized for vegetation growth. Hydrologic restoration enhanced elevation resilience and climate benefits of these coastal wetlands.

Seasonal Variation in Soil and Herbage CO2 Efflux for a Sheep-Grazed Alpine Meadow on the North-East Qinghai-Tibetan Plateau and Estimated Net Annual CO2 Exchange.

The Qinghai-Tibetan Plateau is a vast geographic area currently subject to climate warming. Improved knowledge of the CO2 respiration dynamics of the Plateau alpine meadows and of the impact of grazing on CO2 fluxes is highly desirable. Such information will assist land use planning. We measured soil and vegetation CO2 efflux of alpine meadows using a closed chamber technique over diurnal cycles in winter, spring and summer. The annual, combined soil and plant respiration on ungrazed plots was 28.0 t CO2 ha−1 a−1, of which 3.7 t ha−1 a−1occurred in winter, when plant respiration was undetectable. This suggests winter respiration was driven mainly by microbial oxidation of soil organic matter. The winter respiration observed in this study was sufficient to offset the growing season CO2 sink reported for similar alpine meadows in other studies. Grazing increased herbage respiration in summer, presumably through stimulation of gross photosynthesis. From limited herbage production data, we estimate the sustainable yield of these meadows for grazing purposes to be about 500 kg herbage dry matter ha−1 a−1. Addition of photosynthesis data and understanding of factors affecting soil carbon sequestration to more precisely determine the CO2 balance of these grasslands is recommended.

Multivariate analysis of images in spectrophotometric methods: Quantification of soil organic matter

Soil organic matter (SOM) is usually quantified by Walkley-Black titration method or using a spectrophotometric method. This study proposes an alternative method for quantification of SOM using digital image from scanner and mathematical algorithms to replace titration and spectrophotometry procedures. For this, after SOM oxidation by potassium dichromate, digital images were acquired. Posteriorly, extraction of RGB color histograms from images have occurred, followed by the use of multivariate calibration method: partial least squares (PLS). Six soil samples were analyzed. We used the Walkley-Black method as reference. SOM was estimated by images using the PLS tool. The new method, besides being a fast, low cost, and more operational alternative, presented statistically equal results in relation to the reference method, as assessed by the Student t-test and F-test at 95 % confidence.

Fractionation of Soil Organic Matter into Labile and Stable Fractions

The present study aims to test and evaluate the efficiency of a new modified method of organic matter evaluation. It allows the assessment of the quality and quantity of the primary soil organic matter and the stable organic fractions separately. The new method was tested in six soil samples of different localities in the Czech Republic. This method is based on observing reaction kinetics during the oxidation of soil organic matter and measuring the cation-exchange capacity of stable organic fractions. The results were compared with classical methods, which rely on the isolation of humic substances, determination of the content of humic acids and fulvic acids and their ratio CHA:CFA, quotient E4/6, and fractionation of soil organic matter according to resistance to oxidation. It turned out that the results of the new modified method are more sensitive in comparison with the results obtained by classical procedures. The linear regression demonstrated the dependence between the amounts of soil organic matter determined by the classical method compared with the modified method. Moreover, the new modified method was found to be faster and not demanding on laboratory equipment. The new method has been improved to be easily repeatable, and some shortcomings of the previous method were eliminated. Based on our results and other recent studies, the modified method may be recommended for the practical evaluation of soil organic matter conditions.

Impact of siltation on the stability of organic matter in drained peatlands

Peatlands are unique ecosystems but when they are drained for agriculture or peat mining, stored carbon is released to the atmosphere as CO2. The aim of the study was to assess the influence of siltation on secondary humification basing on humification indicators (C/N ratio, humification degree, humification index, E4/E6 ratio). It is essential to examine to what extent siltation hampers soil organic matter (SOM) oxidation. The study revealed that after drainage the amount of humus fractions, both acid and alkali soluble, were increasing at the expense of non-soluble carbon pool (residuum). Siltation hampered the transformation of organic matter and the quantities of OC and N in humus fractions were lower in silted soil samples than in not silted ones. The carbon extracted in acid-soluble fraction was not related to the state of siltation and was associated with the depth. The nitrogen content in this fraction did not change after drainage or siltation. The siltation did not affect C/N ratios. In unaltered peats these ratios were typical for fen soils (lowland peats) but in other studied soil samples the values of the C/N ratios suggested secondary transformation. The humification indicators (HI, HD and E4/E6) also revealed that secondary humification was more advanced in strongly silted soils, i.e. the stability of SOM in these soils is lower and the values of these indicators were dependent on the state of siltation. The study revealed that both drainage and siltation of soils changed the relations in SOM fractions. Drainage of peatlands resulted in initiation of the secondary humification of SOM and increase of chemically extractable humus fractions as well as increase of the humification degree. Stable SOM, which can have a mean residence time of centuries, became a potential source of CO2. However, siltation which led to a 50% decrease in SOM, hampered oxidation of SOM and had a stabilizing effect on SOM quality. These findings provide new insights into possibilities of mitigation of C losses from agricultural areas and may serve as a guidance for soil C management.

Contribution of the Fenton reaction and ligninolytic enzymes to soil organic matter mineralisation under anoxic conditions

Mechanisms of carbon dioxide (CO2) release from soil in the absence of oxygen were studied considering the Fenton process, which encompasses the reaction of H2O2 with Fe(II) yielding a hydroxyl radical (OH), in combination with manganese peroxidase (MnP) and lignin peroxidase (LiP). This study aimed to explain the high rate of soil organic matter (SOM) mineralisation and CO2 release from humid temperate rainforest soils under oxygen-limited conditions. The investigated mechanisms challenge the traditional view that SOM mineralisation in rainforest is slow due to anaerobic (micro)environments under high precipitation and explain intensive CO2 release even under oxygen limitation. We hypothesised that the Fenton reaction (FR) greatly contributes to the CO2 released from SOM mineralised under anaerobic conditions especially in the presence of ligninolytic enzymes. We used a novel technique that combines labelled H218O2 and Fe(II) to induce the FR and measured CO18O, Fe(II) solubilisation, and peroxide consumption in a closed gas circulation system for 6 h. Maximal CO2 amount was released when the FR was induced in combination with LiP addition. The CO2 efflux with LiP was 10-fold that of abiotic FR reactions without enzymes, or in soils amended with MnP. This was consistent with i) the contribution of 18O from peroxide to CO2 release, ii) peroxide consumption, and iii) Fe(II) solubilisation by FR. The amount of consumed peroxide was closely correlated with the CO18O derived from soil without enzyme addition or with LiP addition. Concluding, abiotic Fenton Reaction coupled with oxidative enzymes, such as LiP, are crucial for SOM oxidation under anaerobic conditions, e.g. in temperate rainforest soils.

Synergy effect of peroxidase enzymes and Fenton reactions greatly increase the anaerobic oxidation of soil organic matter

In temperate rainforest soils of southern Chile (38 °S), there are high rates of soil organic carbon (SOC) mineralization under oxygen (O2) limitation. We study the combined effects of Fenton reactions and the activity of two enzymes manganese peroxidase (MnP) and lignin peroxidase (LiP), which was hypothesised potentiate SOC mineralization under anoxic conditions leading to carbon dioxide (CO2) release. Both mechanisms produce free radicals when competing for SOC oxidation in the absence of microorganisms. We quantify the CO2 release by induced Fenton reactions in combination with MnP and LiP under aerobic and anaerobic conditions (20 °C, 36 h) in temperate rainforest soils. CO2 levels released by Fenton reactions and enzyme activity were eight times higher than those released by Fenton reaction and peroxidase enzymes in individual treatment. Approximately 31% of the CO2 released under aerobic soil incubation was found to be abiotic (sterilized), while 69% was biotic (non-sterilized soils), and respective values of 17% and 83% were recorded under anaerobic conditions. The relative fluorescence intensity clearly shows ·OH radicals production from Fenton reactions. In conclusion, levels of MnP and LiP coupled with Fenton reactions strongly increase SOC mineralization under long periods of O2 limitation in temperate rainforest soils.

Oriented oxidation of all alkanes in soils

In order to investigate the mechanism of the oriented oxidation of all alkanes by regulating organic functional groups, Fenton oxidation was performed in two soils (S1 and S2: total petroleum hydrocarbons (TPH) are 26,281 mg/kg and 12,668 mg/kg). The higher the proportion of hydroxyl radicals (OH) transferred (41 %–58 %), the more the number of oriented oxidation of alkanes, which realized the oriented oxidation of all alkanes. Meanwhile, high oriented oxidation of long alkanes and short alkanes (58 %: 3405 mg/kg and 1729 mg/kg) was observed. Protein Ⅰ in soil organic matter (SOM) was reduced by regulating CH and carboxyl group OH, which indicated that protein Ⅰ was inactive. Protein Ⅰ oxidation after regulation was decreased significantly. Protein Ⅰ was the main active organic matter to capture OH. When the relative reactivity coefficient KTPH/SOM (the ratio of TPH oxidation to SOM oxidation) and KTPH/protein I (the ratio of TPH oxidation to protein Ⅰ oxidation) were higher than 1, low oxidation of SOM and protein Ⅰ was obtained. It indicated that for the oriented oxidation of all alkanes, the high coefficient of relative reactivity for petroleum was the key for the transfer of OH from oxidizing SOM to oxidizing alkanes.

Biomass crops as a soil amendment in cultivated histosols: Can we reach carbon equilibrium?

AbstractPeatlands are known to perform essential economical, societal and regulating functions. Once they are drained to provide optimal crop growth conditions, however, a series of degradation processes is generated. Wind and water erosion, subsidence and soil organic matter oxidation are the main causes of degradation observed in cultivated histosols. This study evaluated the decomposition dynamics and chemical changes of three biomass crops during an in‐situ incubation in a cultivated histosol. The decomposition dynamics characterized in the field study were then used in a simulation to determine if sustainability could be reached by using biomass crops as a soil amendment. The results showed that an exponential decay fitting curve best represented the weight loss of sorghum [Sorghum bicolor (L.) Moench] in the in‐situ bags over time, while a logistic fitting curve best represented that of miscanthus (Miscanthus X giganteus) and willow (Salix miyabeana). The quality of the crop determined the initial and overall decomposition dynamics observed. The loss of carbon from the crushed biomass crop was much more important in sorghum than in miscanthus and willow. The long‐term simulation of histosol amendment revealed that using miscanthus and willow at input rates of 7.5 and 10 T of carbon per year, respectively, would be sufficient to ensure sustainability. Improving knowledge on carbon loss in cultivated histosols as related to soil and crop management would help in developing a soil amendment program at the farm scale. In addition, more knowledge is needed to determine the impact of long‐term and successive amendment with biomass crops on the physical and biochemical properties of histosols.

Impacts of tillage practices on soil carbon stocks in the US corn-soybean cropping system during 1998 to 2016

Tillage alters the thermal and wetness conditions in soil, which facilitates soil organic matter oxidation and water transportation, leading to rapid depletion of soil carbon (C). Little is known about tillage intensity change (TIC) and its impacts in the US corn-soybean rotation system over the past two decades. Using time-series tillage maps developed from a private survey and a process-based land ecosystem model, here we examined how tillage intensity has changed across the nation and affected soil organic carbon (SOC) storage from 1998 to 2016. Results derived from the combination of tillage survey data and cropland distribution maps show that total corn-soybean area consistently increased from 62.3 Mha in 1998 to 66.8 Mha in 2008 and to 73.1 Mha in 2016, among which the acreage under no-till system increased from 16.9 Mha in 1998 to 28.9 Mha in 2008, while conservation and conventional tillage decreased by 3.8 and 3.9 Mha, respectively. The extent of no-till practice in corn-soybean lands shrank by 2.6 Mha from 2008 to 2016, while conservation and conventional tillage increased by 2.8 and 6.1 Mha in the same period. Modeling simulations reveal that historical tillage practices led to a soil C loss of 10.3 (spring till only) to 15.2 (tilled in both spring and fall) Tg C yr−1 in the study area from 1998 to 2016. In addition, reduced tillage intensity in corn-soybean cropland contributed to SOC accumulation at 1.0 Tg C yr−1 (1.6 g C m−2 yr−1) from 1998 to 2008, but the SOC gain was offset by SOC reduction at 2.4 Tg C yr−1 (3.4 g C m−2 yr−1) from increased tillage intensity during the period 2008–2016. For both periods, TIC-induced hydrological C loss accounted for 15% of the SOC change, while the rest was attributed to gaseous-C loss.

Distribution of methane and carbon dioxide concentrations in the near-surface zone over regional fault zones and their genetic characterization in the Pszczyna-Oświęcim area (SE part of the Upper Silesian Coal Basin, Poland)

The objective of this paper was to characterize the variability of methane (CH4) and carbon dioxide (CO2) concentrations in the near-surface zone, measured along 4 selected sampling lines positioned perpendicularly to regional fault zones, in the SE part of the Upper Silesian Coal Basin (USCB), Poland. This way it was possible to check the migration activity of these gases to the surface through low-permeable Miocene strata. It was also possible to evaluate the applicability of surface geochemical survey methodology to the identification of potential accumulations of free natural gas in the topmost parts of the Carboniferous formations in the USCB. The results of 319 soil-gas samples were supported by stable isotope analyses and related to the geological setting and the distribution of methane potential at various depths. Moreover, the sampling included the area of the closed and remediated Andrzej VII mining shaft, where 5 soil-gas samples were taken. Additionally, gas flux was evaluated at 3 measurement points at which increased gas concentrations were detected. The maximum concentrations of CH4 and CO2 in soil gases were 15.4 and 9.39 vol%, respectively. Soil gases contain both thermogenic and microbial CH4 and CO2 that migrated from secondary and primary gas zones within the Pennsylvanian coal-bearing strata. In some sites, CO2 was also generated by the oxidation of soil organic matter and/or CH4 in a near-surface zone. Anomalous CH4 concentrations were generally found over elevated fragments of erosional structures of Carboniferous coal-bearing formations. This indicates the presence of free CH4 accumulations beneath the Miocene overburden. However, the surface anomalies did not always correlate with the zones of CH4 secondary accumulations. Anomalous concentrations of CH4 and CO2 correlated with the regional fault zones that cut through the Carboniferous formations. This indicates the potential presence of fault traps saturated with free CH4 in the upper parts of Carboniferous formations. Relatively low values were observed for both CH4 and CO2 emissions (maximum: 25 and 4320 mg m−2 d−1, respectively). This suggests relatively low dynamics of gas migration from the depth to the soil zone.

A benchmark for soil organic matter degradation under variably saturated flow conditions

Soil contains the largest terrestrial pool of organic matter, and the cycling of organic carbon in soils plays a crucial role in controlling atmospheric carbon dioxide (CO2) and global climate change. Although considerable progress has been made in previous modeling studies on the fate of soil organic matter (SOM), only a few models used a process-based approach for investigating these strongly coupled and complex soil systems, which involve SOM oxidation, transient water flow, and mass transport processes in aqueous and gaseous phases. Typically, physically based models for water flow, as well as solute and gas transport, are not coupled with state-of-the-art SOM degradation models. Reactive transport models (RTMs) provide a flexible framework for implementing different SOM degradation concepts and integrating biogeochemical processes with water flow and mass transport. Given the complex nature of carbon cycling in soils coupled with flow and mass transport, code intercomparison using well-defined benchmarks is in many cases the only practical method of model verification. The benchmark presented in this manuscript focuses on SOM oxidation under variably saturated flow conditions. The benchmark consists of three problems characterized by increasing complexity. The problems were solved using two different reactive transport codes, namely HP1 and MIN3P-THCm. The first supporting problem introduces a batch-type simulation to assess kinetic networks of SOM degradation. In the second supporting problem, transient water flow, solute transport, gas generation, and diffusive gas transport are considered. The principal problem combines the kinetic networks of SOM degradation with reactive transport under variably saturated flow conditions, including CO2 transport from soils to the atmosphere. Simulation results for the benchmark problems demonstrate an overall excellent agreement between the two codes, building confidence in the ability of RTMs to simulate complex C-cycling in dynamic environments.

Microbial Activity and Decomposition of Soil Organic Matter in Roadside Soils Contaminated With Petroleum Hydrocarbons

Petroleum hydrocarbons (PHs) are the most widespread organic pollutants of roadside soils, the reclamation of which is costly due to large areas affected, and natural PHs biodegradation is the only way of mitigating negative ecological consequences. This study aimed to investigate the microbial response to PHs in roadside soils and to identify soil organic matter (SOM) and PHs involved in biodegradation processes. To address this aim, soil respiration is related to light (chain‐length ≤C14) medium (C15–C27), and heavy fractions (≥C28) of total PHs, and to SOM components: carbohydrates, proteins, lignin, aliphates, carbonyl/carboxyl, and char amounts of soils sampled at distances of up to 100 m from three roads in Kharkiv, Ukraine. A close relation between soil respiration and ratio of the light fraction to the sum of medium and heavy alkane fractions indicate the preferential mineralization of more biodegradable light PHs fractions. A positive relation between soil respiration and carbohydrate C, as well as negative correlation with aliphatic C, indicate preferred degradation of carbohydrates compared to more recalcitrant aliphates. Carbohydrate content increased and aliphatic C decreased with distance from the roads, and carbohydrates decreased with PHs concentration, indicating increased degradation of carbohydrates at high PHs concentrations (positive priming). It is concluded that microorganisms generate the energy required for PHs degradation by enhanced oxidation of native SOM where carbohydrates were of paramount importance.

Mineral surface-reactive metabolites secreted during fungal decomposition contribute to the formation of soil organic matter.

Soil organic matter (SOM) constitutes the largest terrestrial C pool. An emerging, untested, view is that oxidation and depolymerization of SOM by microorganisms promote the formation of SOM-mineral associations that is critical for SOM stabilization. To test this hypothesis, we performed laboratory-scale experiments involving one ectomycorrhizal and one saprotrophic fungus that represent the two major functional groups of microbial decomposers in the boreal forest soils. Fungal decomposition enhanced the retention of SOM on goethite, partly because of oxidative modifications of organic matter (OM) by the fungi. Moreover, both fungi secreted substantial amounts (>10% new biomass C) of aromatic metabolites that also contributed to an enhanced mineral retention of OM. Our study demonstrates that soil fungi can form mineral-stabilized SOM not only by oxidative conversion of the SOM but also by synthesizing mineral surface-reactive metabolites. Metabolites produced by fungal decomposers can play a yet overlooked role in the formation and stabilization of SOM.

Resource Legacies of Organic and Conventional Management Differentiate Soil Microbial Carbon Use.

Long-term contrasts in agricultural management can shift soil resource availability with potential consequences to microbial carbon (C) use efficiency (CUE) and the fate of C in soils. Isothermal calorimetry was combined with 13C-labeled glucose stable isotope probing (SIP) of 16S rRNA genes to test the hypothesis that organically managed soils would support microbial communities with greater thermodynamic efficiency compared to conventional soils due to a legacy of lower resource availability and a resultant shift toward communities supportive of more oligotrophic taxa. Resource availability was greater in conventionally managed soils, with 3.5 times higher available phosphorus, 5% more nitrate, and 36% more dissolved organic C. The two management systems harbored distinct glucose-utilizing populations of Proteobacteria and Actinobacteria, with a higher Proteobacteria:Actinobacteria ratio (2.4 vs. 0.7) in conventional soils. Organically managed soils also harbored notable activity of Firmicutes. Thermodynamic efficiency indices were similar between soils, indicating that glucose was metabolized at similar energetic cost. However, differentially abundant glucose utilizers in organically managed soils were positively correlated with soil organic matter (SOM) priming and negatively correlated to soil nutrient and carbon availability, respiration, and heat production. These correlation patterns were strongly reversed in the conventionally managed soils indicating clear differentiation of microbial functioning related to soil resource availability. Fresh C addition caused proportionally more priming of SOM decomposition (57 vs. 51%) in organically managed soils likely due to mineralization of organic nutrients to satisfy microbial demands during glucose utilization in these more resource deprived soils. The additional heat released from SOM oxidation may explain the similar community level thermodynamic efficiencies between management systems. Restoring fertility to soils with a legacy of nutrient limitation requires a balanced supply of both nutrients and energy to protect stable SOM from microbial degradation. These results highlight the need to consider managing C for the energy it provides to ıcritical biological processes that underpin soil health.

Kinetics of soil dehydrogenase in response to exogenous Cd toxicity

Soil dehydrogenase plays a role in the biological oxidation of soil organic matter and can be considered a good measure of the change of microbial oxidative activity under environmental pollutions. However, the kinetic characteristic of soil dehydrogenase under heavy metal stresses has not been investigated thoroughly. In this study, we characterized the kinetic characteristic of soil dehydrogenase in 14 soil types, and investigated how kinetic parameters changed under spiked with different concentrations of cadmium (Cd). The results showed that the Km and Vmax values of soil dehydrogenase was among 1.4–7.3mM and 15.9–235.2μMh−1 in uncontaminated soils, respectively. In latosolic red soil and brown soil, the inhibitory kinetic mechanism of Cd to soil dehydrogenase was anticompetitive inhibition with inhibition constants (Ki) of 12 and 4.7mM, respectively; in other soils belonged to linear mixed inhibition, the values of Ki were between 0.7–4.2mM. Soil total organic carbon and Ki were the major factors affecting the toxicity of Cd to dehydrogenase activity. In addition, the velocity constant (k) was more sensitive to Cd contamination compared to Vmax and Km, which was established as an early indicator of gross changes in soil microbial oxidative activity caused by Cd contamination.

模拟火干扰对森林土壤微生物活性及氮矿化的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 模拟火干扰对森林土壤微生物活性及氮矿化的影响 DOI: 10.5846/stxb201512142483 作者: 作者单位: 中南林业科技大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（31470659） Simulating the effects of fire disturbance on microbial activity and nitrogen mineralization in forest soil Author: Affiliation: Central South University of Forestry Technology Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:火干扰产生热能从而诱导土壤有机质的化学氧化，改变碳和氮转换，对土壤的结构与功能产生严重影响，影响程度取决于火强度、火干扰持续时间和热渗透。在湖南省株洲市高枧林场选取马尾松次生林火烧迹地，按两种土壤、3个温度和3种土壤水势进行试验设计与方差分析，探讨火干扰对土壤微生物及氮矿化的影响。结果表明：无机氮的浓度与火强度和初始土壤有机质含量呈正相关关系；火干扰后短期内土壤碳和氮浓度较高，微生物生物量碳和潜在可矿化氮较低，温度和土壤水势对基础呼吸速率没有显著影响；当土壤温度达160℃时，未受火干扰土壤中潜在可矿化氮浓度迅速不稳定增加，温度达350℃时破坏90%的非微生物组织；土壤加热后水势对氮矿化过程有显著影响，水势越高，潜在可矿化氮损失越大，火干扰土壤的含水量与硝态氮之间呈正相关关系；培养14 d期间，土壤火灾历史、热处理和土壤水势对微生物活性、碳和氮矿化有显著影响，-1.5 MPa水势下加热到380℃后两种土壤的微生物生物量碳含量最高，土壤水势和可溶性糖呈负相关关系；水势和火干扰之间的交互作用显著影响微生物活性和氮转换，低水势土壤中的微生物生物量碳、可溶性糖和潜在可矿化氮浓度较高。 Abstract:Heat from fire disturbance induces chemical oxidation of soil organic matter that alters the conversion of carbon (C) and nitrogen (N), which seriously influences soil structure and functions. However, the extent of oxidation depends on the fire intensity and duration, and heat penetration. In the present study, a burned area of Pinus massoniana secondary forest located in the Gaojian State Forest Farm, Zhuzhou, Hunan Province, was selected to conduct an experiment of the effects of fire disturbance on microbial activity and N mineralization of forest soil. The experiment was conducted in a completely randomized design based on two kinds of soil, three different temperatures, and three soil water potentials, with each treatment replicated three times. A variance analysis was performed on the data. The results showed the concentration of inorganic N and initial soil organic matter content were positively correlated with fire intensity. Shortly after fire disturbance, soil C and N concentration were high, but microbial biomass C and potentially mineralized nitrogen (PMN) were low, and temperature and soil water potential had no significant effect on the basic respiration. PMN loss was observed in the unheated control soils of fire disturbance compared with soils not exposed to fire. When soil temperature reached 160℃, it resulted in only a modest increase in PMN concentrations in the soil not previously exposed to fire. If soil temperature exceeded 160℃, the PMN content fluctuated, and then increased rapidly. A soil temperature of 350℃ resulted in the destruction of 90% non-microbial tissues. The soil water potential after heating had a significant effect on N mineralization:the higher the soil water potential, the more the PMN loss. There was a positive correlation between the water content of fire disturbed soil and nitrate N. During the 14 day incubation, microbial activity and C and N mineralization were significantly influenced by soil fire history, initial heat treatment, and soil water potential. The release of soil available C and N from fire disturbance supported the recovery of microbial activity in low water potentials. When soil was heated to 380℃ at -1.5 MPa water potential, soil microbial biomass C was the highest in both soils. A negative correlation between soil water potential and soluble sugar was observed for both soils. The concentration of soluble anthrone reactive carbon (ARC) dropped significantly(P<0.05) in both soils over time, resulting from the microbial consumption of sugars released from the fire disturbance. The interaction between water potential and fire disturbance significantly affected the microbial activity and N conversion, and in low water potential soil, microbial biomass C, soluble sugar, and PMN were high. Newly formed labile N by fire disturbance was protected in soil with low water potential. Labile N remained lower in moist than in dry soils regardless of soil fire history. 参考文献 相似文献 引证文献