Organic Matter Carbon 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.

A stable isotopic approach for quantifying aquaculture-derived organic matter deposition dynamics in the sediment of a coastal fish farm

The stable carbon and nitrogen isotopic compositions (δ13C and δ15N) of sedimentary organic matter (OM) in fish farms (FFs) were investigated to quantify the aquaculture-derived OM deposition dynamics in the sediment. The dual isotopic compositions of mixed OMs in surface sediments at FFs differed significantly (p < 0.05) from those at reference sites, indicating an increased deposition of fish feces or uneaten feed in the sediments. Furthermore, OM source apportionments revealed that the quantitative contribution of fish feces (23.3 mg g−1 dw) during farming activities was significantly higher than that of other natural OM sources (C3 plants and phytoplankton). After the disassembly of fish cages, the deposited fish feces may be preferentially degraded through processes that require a large amount of oxygen consumption (<0.1 kg C m−2 yr−1). Our isotopic approach may be helpful for assessing the impact of FF wastes and for taking measures to minimize environmental deterioration.

Updating the dual C and O isotope-Gas-exchange model: A concept to understand plant responses to the environment and its implications for tree rings.

The combined study of carbon (C) and oxygen (O) isotopes in plant organic matter has emerged as a powerful tool for understanding plant functional responses to environmental change. The approach relies on established relationships between leaf gas exchange and isotopic fractionation to derive a series of model scenarios that can be used to infer changes in photosynthetic assimilation and stomatal conductance driven by changes in environmental parameters (CO2 , water availability, air humidity, temperature, nutrients). We review the mechanistic basis for a conceptual model, in light of recently published research, and discuss where isotopic observations do not match our current understanding of plant physiological response to the environment. We demonstrate that (1) the model was applied successfully in many, but not all studies; (2)although originally conceived for leaf isotopes, the model has been applied extensively to tree-ring isotopes in the context of tree physiology and dendrochronology. Where isotopic observations deviate from physiologically plausible conclusions, this mismatch between gas exchange and isotope response provides valuable insights into underlying physiological processes. Overall, we found that isotope responses can be grouped into situations of increasing resource limitation versus higher resource availability. The dual-isotope model helps to interpret plant responses to a multitude of environmental factors.

Diversifying with grain legumes amplifies carbon in management-sensitive soil organic carbon pools on smallholder farms

Crop diversification with grain legumes has been advocated as a means to increase agroecological resilience, diversify livelihoods, boost household nutrition, and enhance soil health and fertility in cereal-based cropping systems in sub-Saharan Africa and around the world. Soil organic carbon (SOC) is a primary indicator of soil health and there is limited data regarding SOC pools and grain legume diversification on smallholder farms where soils are often marginal. In Malawi, a range of legume diversification options are under investigation, including rotations and a doubled-up legume rotation (DLR) system in which two compatible legumes are intercropped and then rotated with a cereal. The impact of the DLR system on SOC has not yet been determined, and there is a lack of evidence regarding SOC status over a gradient of simple to complex grain legume diversified systems. We address this knowledge gap by evaluating these systems in comparison to continuous sole maize (Zea mays L.) at three on-farm trial sites in central Malawi. After six years of trial establishment, we measured SOC in bulk soils and aggregate fractions and in faster cycling SOC pools that respond more rapidly to management practices, including water extractable organic carbon (WEOC), particulate organic matter carbon (POM-C), potentially mineralizable carbon (C), and macroaggregate C. Cropping treatment differences were not seen in bulk SOC or total N, but they were apparent in SOC pools with a shorter turnover time. The DLR system of intercropped pigeonpea (Cajanus cajan (L.) Millsp.) and groundnut (Arachis hypogaea L.) rotated with maize had higher WEOC, POM-C, potentially mineralizable C, macroaggregate and microaggregate C values than continuous maize. Of the single legume rotations, the pigeonpea-maize rotation had more mineralizable C and microaggregate C compared to continuous maize, while the groundnut-maize rotation had similar C values to the maize system. Overall, this study shows the potential for crop rotations diversified with grain legumes to enhance C in management sensitive SOC pools, and it is one of the first reports to show this effect on smallholder farm sites.

Investigation on the Mineral Catalytic Graphitization of Anthracite during Series High Temperature Treatment

Graphite can be artificially converted from anthracites under high temperatures; however, the exact mechanism through which inorganic minerals contribute to the graphitization process is still unknown. In light of this, several selected minerals in different amounts were added to demineralized anthracite coal. The anthracite–mineral mixtures were subjected to artificial graphitization experiments under temperatures ranging from 1700 to 2900 °C in the laboratory. The obtained series of coal-based graphites with various levels of graphitization were characterized by X-ray diffraction (XRD), and the derived structural parameters, such as d002 and FWHM (002), La, and Lc were used to compare the carbon structural evolution during the high temperature treatment and mineral catalytic graphitization. Moreover, the amorphous carbon of anthracite is eventually transformed into the highly ordered crystalline carbon of coal-based graphite. The five added minerals show interesting structural variation during the graphitization process, in which pyrite is decomposed into iron (Fe), illite, quartz, and kaolinite, which can react with disordered carbon in organic matter to form moissanite (SiC), while dolomite seems to react with sulfur to form oldhamite (CaS). At temperatures less than 2300 °C, the minerals could significantly enhance the catalytic effect. There is a clear difference in the catalytic effect of different minerals on graphitization. Kaolinite exhibits the strongest catalytic effect. The minerals dolomite, illite, and quartz only show a certain degree of catalysis. Pyrite, however, only has a limited effect on improving the degree of graphitization at a temperature of 1700 °C. However, once the temperature exceeds 2300 °C, the dominant factor controlling the graphitization of anthracite appears to be the temperature. According to the growth pattern at microcrystalline sizes (La and Lc), the minerals’ catalytic effects can be classified into three groups. The first group includes minerals that preferentially promote La growth, such as pyrite, illite, and quartz. The second group includes minerals that preferentially promote Lc growth, such as dolomite. Finally, kaolinite is in a separate group that promotes microcrystal growth in both the lateral and vertical directions simultaneously. The mechanisms of the minerals’ catalytic graphitization are discussed in this paper. The promotion role of minerals in the artificial graphitization process may help to optimize the graphitization process and reduce the process cost in the future.

Limited impacts of occasional tillage on dry aggregate size distribution and soil carbon and nitrogen fractions in semi-arid drylands

Tillage management that minimizes the frequency and intensity of soil disturbance can increase soil carbon (C) and nitrogen (N) sequestration and improve the resilience of dryland cropping systems, yet the impact of occasional disturbance on soil aggregate formation and the soil organic carbon (SOC) storage within aggregates has not been studied well. We evaluated the effect of four tillage management practices on soil dry aggregate size distribution, aggregate-protected C and N, mineral-associated organic matter carbon (MAOM-C), particulate organic matter carbon (POM-C), and corn (Zea mays L.) and sorghum (Sorghum bicolor (L.) Moench) yields in a semi-arid dryland cropping system. Treatments included conventional tillage (CT), strip-tillage (ST), no-tillage (NT), and occasional tillage (OT) management in a corn-sorghum rotation. Soil macro-aggregates were 51–54% greater under ST, NT, and OT, while small and micro-aggregates were greater in CT. Conventional tillage reduced soil aggregate-associated C by 28–31% in macro-aggregates and 47–53% in small aggregates at 26 months (M) sampling compared to ST, NT, and OT. In clay + silt fraction, CT had 14–16%, 21–26%, and 36–43% less SOC at 7, 14, and 26M samplings, respectively, than ST, NT, and OT. Aggregate associated N was generally similar under ST, NT, and OT, which was greater on average than CT. Soil MOAM-C and POM-C under ST, NT, and OT were generally greater than respective SOC fractions under CT at 19 and 26 M after OT implementation. Corn and sorghum yields were similar among tillage systems in 2020, but greater under ST, NT, and OT than CT in 2021. Our results suggest that while frequent intensive tillage can lower SOC and N storage, a single stubble mulch occasional tillage after several years of NT does not lead to soil C and N losses and soil structural instability in semi-arid drylands.

Rapid increase of surface water pCO2 revealed by settling particulate organic matter carbon isotope time series during 2001–2009 in Sagami Bay, Japan

Rapid increase of surface water pCO2 revealed by settling particulate organic matter carbon isotope time series during 2001–2009 in Sagami Bay, Japan

Labile organic matter and fertility of chernozems

Soil organic matter can be divided into stable and labile, with the latter directly supporting plant growth and development during the growing season. To restore soil fertility and ensure high productivity of agrocenoses, a certain ratio between the labile and stable parts of humus must be maintained. The purpose of this study was to determine the content of labile organic matter under different tillage and fertilisation options and to establish the optimal ratio between their content and the content of total carbon, based on which to develop measures to restore and improve the fertility of chernozem soils. In stationary experiments, the study investigated the impact of the intensity of chernozem use, its cultivation and fertilisation systems on the humus state of the amount of labile organic matter and its ratio to humus carbon. Field research, laboratory method of soil sample analysis, systematisation, analysis, and generalisation were used in the study. The soil samples were analysed for humus content according to DSTU 4289:2004 and labile organic matter content according to DSTU 4732:2007. When chernozems are ploughed up, labile organic matter is mineralised the most and their share in humus decreases, while when arable land is converted to fallow land, it is restored the fastest. Minimising tillage systems and applying organic and mineral fertilisers increases the amount of labile organic matter in the humus of chernozems. The use of no-till for sixteen years resulted in a 0.13% increase in humus content, and a 0.53% increase over forty-two years compared to ploughing. The application of organo-mineral fertiliser increased the ratio of labile organic matter carbon content to total carbon content compared to the unfertilised variants. A strong correlation was found between the content of labile organic matter in chernozems and the yield of winter wheat and maize. The practical significance of the research results is to minimise the fertiliser rate and the C:N ratio to ensure gross crop yields and restore soil fertility

Assessment of the Impact of Industry-Related Air Emission of Arsenic in the Soils of Forest Ecosystems

The soils of forest ecosystems are often affected by the industrial activity of mining and metallurgical enterprises, and insufficiently investigated for the content of pollutants due to enterprise emissions. Some pollutants, such as arsenic, are transported over long distances by these emissions. To analyze this connection, the present study was conducted on the eastern slope of Mount Yurma, the Southern Urals, Russia, to determine the content of arsenic in the soils of mountain forest areas in the impact zone of the copper smelter (Karabash). The physical and chemical parameters, total content of arsenic, mineralogical composition of silt, and concentration of arsenic in the silty fraction in soils located at different altitudes were determined using atomic absorption spectroscopy (AAS) and X-ray diffraction (XRD) techniques. The soils under study are physico-chemically and chemically acidic in the upper horizons with a pH of 3.26 to 4.05. The carbon of organic matter decreases with depth from 7.98 to 0.06%. Exchangeable Ca and Mg cations in the range of 2.6–8.6 mg-eq per 100 g of soil were determined. The mineralogical composition of the silty fraction consists mainly of quartz and aluminosilicates. Following an analysis of the arsenic content in the above-ground leaf litter, the bioconcentration factor (BCF) was calculated. Arsenic exceeding Clarke concentrations was recorded. In all upper soil horizons, concentrations of total arsenic exceeded background values by 3.7–5.2 times, with maximum values in the horizons A—25.3 mg/kg, in the horizons O—64.4 mg/kg. The obtained BCF &gt; 1 data points to the biological arsenic accumulation by plants and, as a result, its input into the soil via industrial emissions from the smelter. It was found that the silty fraction plays a special role in the accumulation of arsenic in the studied soils. Accumulation of arsenic occurred mainly due to the secondary minerals of Ca and Mg. Differences in the accumulation of arsenic in the forest litter depending on the plant association were noted. The obtained results could serve as a guideline for monitoring the areas around the enterprise and enhancing the understanding of pollutants’ distribution in the soils of remote areas and mountain landscapes.

Carbon and nitrogen stable isotope measurements of bulk organic matter in sediments from Obanul Mare paleolake, Mangalia, Romania

Carbon and nitrogen stable isotope measurements of bulk organic matter in sediments from Obanul Mare paleolake, Mangalia, Romania

Carbon cycle during the late Aptian–early Albian OAE 1b: A focus on the Kilian–Paquier levels interval

The Oceanic Anoxic Event (OAE) 1b took place over a protracted time interval during the Aptian/Albian boundary interval, at the dawn of the mid-Cretaceous climatic optimum. OAE 1b is characterized by the occurrence of several sub-events recorded by organic matter-rich levels, which can be traced on regional-to-global scale. Previous studies have highlighted that the climax of the event occurred around the Kilian – Paquier interval, with this latter sub-event being the most extended and pronounced stratigraphic interval. Numerous studies on OAE 1b have however only focused on high-precision investigations of the Kilian and/or Paquier levels, leaving vast uncertainties about the environmental changes and their drivers during the entire OAE 1b, and hence also on the mechanisms leading to the formation of the sub-events themselves. In this study, we have performed a high-resolution multi-proxy analysis of the Briers section, a well-exposed section in the Blue Marls Formation of the SE France Vocontian Basin, continuously covering the Kilian – Paquier interval. Pyrolysis analyses show that most of the organic matter in this section is immature and of continental origin, averaging 1.5% TOC. The Kilian and Paquier levels are characterized by higher TOC values and a substantial increase in the amount of marine organic matter. Comparing TOC values with changes in Al or Ti concentration (proxies for continental weathering) and Hydrogen index (HI values, tracer for the type of organic matter) reveals that the background long-term change in TOC is linked to change in the continental organic matter delivery to the Vocontian Basin tied to changes in continental weathering rates. Sporadic increases in TOC values associated with the Kilian, HN 8, and Paquier levels, are most likely the result of short-lived events of increased marine primary productivity and organic matter preservation superimposed on the background influx of continental organic matter. A high-resolution bulk organic matter carbon isotope record shows that, apart from the Paquier level, all the fluctuations observed in the carbonate carbon isotope ratios are also mirrored in the organic matter record, although with higher amplitudes. This discrepancy in amplitude can be resolved by correcting the bulk organic matter carbon isotope record for fluctuations in the type of organic matter, demonstrating that both oceanic and atmospheric reservoirs were affected by similar carbon isotope fluctuations, which were hence of global extent. The abnormal bulk organic matter carbon isotope record of the Paquier level further confirms the large geographical expansion of unusual organic matter production and/or accumulation during this peculiar event. Overall, this study suggests that Milankovitch-paced (long eccentricity) changes in monsoonal activity and their effect on the accumulation of organic matter in continental wetlands best explains the rhythmic change in the global carbon isotope record across the OAE 1b interval.

Unique benthic foraminiferal communities (stained) in diverse environments of sub-Antarctic fjords, South Georgia

Abstract. Sub-Antarctic fjords are among the environments most affected by the recent climate change. In our dynamically changing world, it is essential to monitor changes in these vulnerable settings. Here, we present a baseline study of “living” (rose-bengal-stained) benthic foraminifera from fjords of South Georgia, including fjords with and without tidewater glaciers. Their distribution is analyzed in the light of new fjord water and sediment property data, including grain size and sorting, total organic carbon, total sulfur, and δ13C of bulk organic matter. Four well-defined foraminiferal assemblages are recognized. Miliammina earlandi dominates in the most restricted, near-shore and glacier-proximal habitats, Cassidulinoides aff. parkerianus in mid-fjord areas, and Globocassidulina aff. rossensis and an assemblage dominated by Ammobaculites rostratus, Reophax subfusiformis, and Astrononion echolsi are in the outer parts of the fjords. Miliammina earlandi can tolerate strong glacial influence, including high sedimentation rates in fjord heads and sediment anoxia, as inferred from sediment color and total organic carbon / sulfur ratios. This versatile species thrives both in the food-poor inner reaches of fjords that receive mainly refractory petrogenic organic matter from glacial meltwater and in shallow-water coves, where it benefits from an abundant supply of fresh, terrestrial, and marine organic matter. A smooth-walled variant of C. aff. parkerianus, apparently endemic to South Georgia, is the calcareous rotaliid best adapted to inner-fjord conditions characterized by moderate glacial influence and sedimentation rates and showing no preference for particular sedimentary redox conditions. The outer parts of fjords with clear, well-oxygenated bottom water are inhabited by G. aff. rossensis. Ammobaculites rostratus, R. subfusiformis, and A. echolsi dominate in the deepest-water settings, with water salinities ≥ 33.9 PSU and temperatures 0.2–1.4 ∘C, characteristic of winter water and Upper Circumpolar Deep Water. The inner- and mid-fjord foraminiferal assemblages seem specific to South Georgia, although with continued warming and deglaciation, they may become more widespread in the Southern Ocean.

Inferring the ecological quality status based on living benthic foraminiferal indices in transitional areas of the Guanabara bay (SE Brazil)

Using benthic foraminifera, we evaluate the ecological quality status (EcoQS) of transitional waters of the Guanabara Bay (SE Brazil) by applying the diversity-based index exp (H′bc) and the sensitivity-based Foram-AMBI for the first time in South America. The Guanabara Bay was selected for this study as it is one of the largest transitional ecosystems in the State of Rio de Janeiro and has been severely impacted by anthropogenic activities. Concentrations of potentially toxic elements (PTEs) were assessed by sequential chemical extraction in three phases (i.e., dissolved in water, adsorbed on organic matter, and Mn oxy-hydroxides). Total organic carbon, total nitrogen, and stable isotope (δ13C and δ15N) signatures of organic matter were analyzed to trace environmental stress. The Ammonia/Elphidium ratio suggests hypoxic conditions at most of the sampled sites. Principal component analysis identifies the first component as environmental stress underlying organic matter and PTE enrichment (in all three phases), which is positively related to Foram-AMBI and negatively to exp (H′bc). The exp (H′bc) and Foram-AMBI indices reveal that stations near the Governador Island and Niterói margin have the worst EcoQS, showing medium to extreme pollution. Additionally, Foram-AMBI and exp (H′bc) provide a congruent EcoQS classification for ∼64% of the sites. Although these results are promising, they suggest that a significant effort should be made to obtain better knowledge of foraminiferal ecological requirements to employ benthic foraminifera as a biomonitoring and management method.

ОСОБЕННОСТИ ИЗОТОПНОГО СОСТАВА УГЛЕРОДА ОРГАНИЧЕСКОГО ВЕЩЕСТВА И УГЛЕРОДА И КИСЛОРОДА КАРБОНАТНОЙ СОСТАВЛЯЮЩЕЙ НЕФТЕГАЗОПРОИЗВОДЯЩИХ ОТЛОЖЕНИЙ КЕМБРИЯ СИБИРСКОЙ ПЛАТФОРМЫ

The paper presents data on the carbon (δ13С) and oxygen (δ18О) isotopic composition of the carbonate rock constituent (CRC) and carbon (δ13C) of dispersed organic matter (SOM) of rocks of the Shumnaya, Inikan and Kuonamka Formations of the Lower-Middle Cambrian of the Siberian Platform. Dependence of the carbon and oxygen isotopic composition of CRC on the facies subtype of domanicoid deposits of the Cambrian was revealed. The interrelation of the carbon isotope composition of DOM with depositional conditions of sediments of the Lower and Middle Cambrian was considered. In the south-east of the Siberian Platform, Lower Cambrian carbonate deposits with carbon anomalous isotopic composition of CRC (δ13Сср = 6,6 ‰) and carbon of DOM (δ13С = –36,5 ‰) were found.

Impact of deforestation on the soil physical and chemical attributes, and humic fraction of organic matter in dry environments in Brazil

Deforestation of Caatinga and inadequate land use of these dry environments have impacted soil quality in Northeastern Brazil. The objectives of this study were: (a) to evaluate the effect of deforestation and different agricultural uses on the physical and chemical properties of soil, and humic fractions of soil organic matter in dry environments; and (b) to detect the soil properties that were most affected by anthropic actions. We evaluated four dry areas in Chapada do Araripe, NE Brazil: preserved native vegetation; degraded native vegetation; cassava conventional cultivation; and eucalyptus agro-energy cultivation. Soil fertility, total organic carbon and humic fractions of soil organic matter were lower in the degraded native vegetation area. The best indicators for soil quality evaluation were: macroporosity; bulk density; soil resistance penetration; sum of bases (mainly Ca2+); available P; and saturation by Al3+. Total organic carbon and humic acid fractions of soil organic matter were important in improving soil quality. These properties were influenced by deforestation and agricultural uses, suggesting that the deforestation of native vegetation in dry environments has high capacity to degrade the soil, preventing its regeneration.

Study of Some Heavy Metals Concentrations from the Soil of Selected Areas at the ‎North Part of Basrah, Iraq

The current study was conducted in the north of Basra to show the state of contamination and how it is affected by different pollutants. including heavy elements and some important environmental indicators of the soil. The study period extended from September 2021 to June 2022 to determine the concentrations of some heavy metals in the soil in (wet-dry) where six elements were estimated, namely zinc, copper, lead, nickel, cadmium, and Iron in the exchangeable phase and the residual phase of the soil Heavy elements have been extracted by standard methods and determined by using an atomic absorption spectrometer, as well as the determination of total carbon organic matter (TOC %) and soil texture. Total organic carbon results are shown in the current study in the soil, where the highest value of total organic carbon (TOC %) was recorded in the dry season in Al-Hawyer region station-1which has a value of 0.480 % and a rate of 0.207 % . The lowest value, was 0.02 % and recorded in the AL-Deer Nillage at station-5, with a rate of 0.183 % but the highest value of carbon in the total organic matter (TOC %) in the wet season was recorded in the Al-Nashwa region (0.615 %) at station with a rate of 0.355 % and the lowest value of 0.125 % was in the Al-Hawyer region station-1, and at a rate of 0.16%. The results of heavy metals for the study area in the soil in the dry season of the exchangeable phase showed that the highest rate of elements (zinc, copper, lead, nickel, cadmium and iron) 60.18, 53.37, 22.95, 57.86, 7.46 and 720 μg/g respectively and the lowest rates recorded were : 20.94, 15.01, 11.96, 23.81, 3.11 and 502.32 μg/g As for the results of heavy elements in the residual phase of the soil (zinc, copper, lead, nickel, cadmium and iron), it recorded the highest rates : 93.24, 20.78, 31.63, 77.82, 9.98 and 751 μg/g where the lowest recorded rates were : 47.29, 8.08, 17.19, 53.28, 9.98 and 550.86 μg/g respectively in the wet season. The heavy weight of the study area in the soil of the exchangeable phase showed that the highest rate of the elements zinc, copper, lead, nickel, cadmium, and iron was: 152.70, 25.35, 20.07, 88.32, 6.73, and 703 μg/g respectively, the lowest recorded rat 17.24, 2.03, 17.10, 20.11, 2.69 and 274 μg/g respectively. The results of heavy metals in the residual phase. The residual zinc element ranged rate between 5.04-41.84 μg/g while the copper element ranged from 0-23.99 μg/g and the lead element ranged from 12.16-24.22 μg/g as for nickel, it ranged between 39.73 and 62.95 μg/g and cadmium ranged from 5.31-10.70 μg/g finally rates of iron elements were also between 504.18 and 721 μg/g.

Low-concentration methanol effect on the microorganisms, nitrogen removal, and recovery of the completely autotrophic nitrogen removal over nitrite.

Methanol has a significant effect on the performance of the completely autotrophic nitrogen removal over the nitrite (CANON) process. In this research, the effect of low-concentration methanol on the functional microorganisms and nitrogen removal and recovery in the CANON system is investigated. The result shows that the anaerobic ammonium-oxidizing bacteria (AnAOB) was suppressed with low-concentration methanol addition, and the phylum Planctomycetes was hidden. The genus Candidatus Brocadia was restrained, and the relative abundances reduced from 25.5 to 15.0% in the upper biofilm and from 20.3 to 14.3% in the bottom biofilm, respectively. However, low-concentration methanol promoted the nitrifying oxidizing bacteria (NOB) activity. This phenomenon reduced the average ammonium nitrogen removal rate from 95.0 to 70.7%, and the average total nitrogen removal rate decreased from 81.3 to 43.6%, respectively. The results demonstrated that the low-concentration methanol as an organic carbon matter harmed the CANON process. Fortunately, the CANON system had an excellent self-healing ability when the methanol was stopped, with the average ammonium nitrogen removal rate and total nitrogen removal rate returning to 95.5 and 80.9%, respectively. This research supplies a reference for practical engineering design and application by improving the understanding of the effects of low-concentration methanol on CANON process performance.

Litter quality and living roots affected the formation of new mineral-associated organic carbon but did not affect total mineral-associated organic carbon in a short-term incubation

Storing carbon (C) in soil organic matter (SOM) is critical for mitigating climate change as well as for providing food security under extreme weather events. Mineral-associated organic matter (MAOM), which is the organic matter attached to silt and clay, has a longer residence time than the light, sand-sized particulate organic matter (POM). Hence, increasing the C in this fraction is thought to be important for long-term C storage. However, the influence of litter quality and living plants on new MAOM formation and MAOM turnover is unclear. We hypothesized that lower C:N litter would form MAOM more efficiently and result in more MOAM than higher C:N litter because lower C:N litter favors biomass production of microbes, which are thought to be an important precursor of MAOM. In addition, we hypothesized that living plants would amplify the effect of litter quality on MAOM formation and turnover because roots growing with low C:N litter would be less N-stressed and rely less on MAOM turnover to access N than roots growing in high C:N litter. We conducted a greenhouse study where soil was mixed with four different plant litter treatments: a control without litter, soybean (Glycine max) with C:N = 21, buckwheat (Fagopyrum esculentum) with C:N = 35, and sudex (Sorghum bicolor [L.] Moench × S. sudanense [P.] Staph.) with C:N = 65. The four litter treatments were incubated with and without living oats (Avena sativa). The incubation was maintained for 40 days, and over this period soybean and buckwheat lost 89 % of their initial dry matter while sudex lost 69 % of its initial dry matter. Contrary to our expectation, the litter with the higher C:N (sudex) had the greatest proportion of degraded C transferred to MAOM (i.e., the litter MAOM-C transfer efficiency). However, the litter MAOM-C transfer efficiency was not associated with the total MAOM-C at the end of the incubation. The presence of living plants increased the amount of MAOM-C derived from soybean and sudex litter, but it did not increase the total MAOM-C. Thus, our results demonstrate that high C:N litter can efficiently form new MAOM-C, which can be enhanced by the presence of living plants, but the greater MAOM-C formation may be accompanied by a loss of pre-existing MAOM-C.

Insights from size fractions to interpret the erosion-driven variations in soil organic carbon on black soil sloping farmland, Northeast China

Declines of soil organic carbon (SOC) and degradation of soil function are caused by long-term soil erosion and cultivation. Although the variations of bulk SOC have been extensively studied, the driving mechanisms of variations in SOC fractions, i.e., carbon in coarse particulate, fine particulate, and mineral-associated organic matter (CPOM-C, FPOM-C, and MAOM-C), and their relationship with soil erosion remain unclear on sloping farmland. In this study, two areas of farmland with different slope types (convex vs. straight) and reclamation periods (50 years vs. ≥100 years) in the black soil region of Northeastern China were chosen to explore the roles of soil erosion on the variations of SOC and their size fractions based on the 137Cs tracer technique. The results showed that the average net erosion rate of the straight slope was 2810.09 t km-2a-1 and the convex slope was 3801.71 t km-2a-1 with higher spatial variability. When compared with uncultivated land, SOC contents of convex and straight slopes have decreased by 13.58% and 35.18%, with a reduced rate of 0.089 g kg-1 a-1 and 0.116 g kg-1 a-1, respectively. Although the CPOM-C fraction showed the most significant relative decreases (over 73.24%), the absolute declines of MAOM-C were more significant, especially in the straight slope with a more extended cultivation period. The contributions of erosion to the SOC decreases on convex and straight slopes were 69.54% and 13.09%, respectively. Erosion exerted a significant influence on finer particles such as FPOM-C and MAOM-C. With increasing cumulative erosion, the absolute magnitude of each SOC fraction in soils decreased. But the proportion of MAOM-C increased, while FPOM-C and CPOM-C decreased. Overall, our findings demonstrated that soil erosion not only induced the loss of SOC fractions but also transformed the proportional distribution of their fractions, and then affected the functions of SOC. Moreover, the effects of tillage (i.e., an increase in microbial activity) on straight slopes are not negligible in farmland that has experienced long-term cultivation but relatively little erosion. Apart from erosion reduction in areas of severe erosion, appropriate fertilization for farmland with a long history of cultivation should also be adapted to achieve sustainable development of black soil resources.

Dissolved organic matter and microbial carbon of Protocalcic Chernozems of different land management

Water-extractable organic matter is the most active and mobile form of soil carbon. The other active fraction and extremely biolabile is the carbon constituent of microorganisms. Both of these fractions play an essential role in agrocenoses and in the global carbon cycle on our planet. The aim of the work was to estimate the carbon content of water-extractable organic matter as well as that of microbial origin in typical chernozems (Protocalcic Chernozems) of different land-use types. Protocalcic Chernozem samples taken from the fields of long-term experiments with different types of land use were investigated: a permanent bare fallow for 55 years (since 1964); conventional tillage – four-field crop rotation, first rotation; direct seeding – crop rotation similar to direct seeding, first rotation; a 21-year fallow (since 1998) after 34 years of bare fallow (since 1964). We determined the carbon content of water-extractable organic matter and the carbon content of microbial origin. In the studied series of variants, the proportion of carbon of water-extractable organic matter in the total amount of organic matter in the upper horizon (0–15 cm) was 0.69, 0.85, 1.01, and 0.98%, respectively, while that of carbon of microbial origin was 0.27, 0.55, 0.53, and 1.52%. It was noted that against the background of increasing the content of total organic carbon in direct seeding variant, compared with the traditional soil treatment, the microbial biomass in this variant does not increase. The fallow variant, unlike all other types of land use, is characterized by a higher proportion of microbial carbon, in contrast to the carbon of water-extractable organic matter.