Oxidation Of Organic Carbon Research Articles

Making Sense of Massive Carbon Isotope Excursions With an Inverse Carbon Cycle Model

AbstractThe beginning and end of the Proterozoic Eon are marked by extreme variations in carbonate carbon isotope values that have been interpreted to record massive perturbations to the global carbon cycle. The lower Proterozoic contains an extended interval of strata characterized by positive carbonate δ13C values. Conversely, uppermost Proterozoic carbonate strata contain thick intervals with extremely negative δ13C values and multiple large swings in carbonate δ13C. Previous attempts to model these pronounced carbon isotope excursions as shifts in the global marine dissolved inorganic carbon (DIC) reservoir have proved to be problematic, as the direction and magnitude of these positive and negative carbon isotope excursions require unrealistic amounts of either organic carbon burial or organic carbon oxidation, respectively. Here we present a modified global carbon cycle model—coupled with oxygen and sulfur cycle mass balances—that includes a parameterization of the recycling of sedimentary isotope anomalies and allows the extent of organic carbon oxidation to vary as a function of atmospheric oxygen levels. Our model is designed to match carbon isotope records while maintaining redox and mass balance with a given set of initial conditions and carbon cycle parameterizations. Using this approach, we demonstrate that there is a range of plausible biogeochemical perturbations that could induce substantial δ13C excursions in the global marine DIC reservoir. However, we also find that there are multiple, nonunique Earth system states for any observed marine δ13C value.

Transient early diagenetic processes in Rhône prodelta sediments revealed in contrasting flood events

Floods carry sediments to river deltas and the coastal zone, but little is known about the geochemical evolution of this particulate material deposited over a short period of time. Here, we studied two recent contrasting flood deposits in the Rhône River prodelta area (northwestern Mediterranean Sea). We monitored the porewater and solid-phase chemistry over periods ranging from a few days to 6 months after deposition. Non-steady state diagenetic processes associated with episodic deposition promote a wide spectrum of transient redox conditions in the shallow prodelta region of the Rhône. Specific attributes of diagenetic responses depend on the sources of flood material and scale (thickness) of deposition.The first flood unit of 20–30 cm was composed of light gray mud, poor in organic carbon and rich in reactive manganese oxides. The short-term responses of early diagenetic processes contrasted with a rapid consumption of O2 and NO3- over a few hours just after the deposition event, accompanied by a slower build-up of Mn2+ concentration, and a lagged response in Fe2+ concentration over a few days or weeks. This difference was due to the redox capacity of the sediment, evolving from oxidized, during the flood layer deposition, to more reducing conditions, after a few days or weeks, allowing Fe2+ to build up and remain in solution. Sulfate reduction may have started within a few days within the flood deposit and was greatly enhanced just below the former redox front due to a fresh input of organic matter (OM). This large production of H2S probably led to the precipitation of sulfide minerals in close vicinity to the former redox front, limiting the accumulation of Fe2+ and H2S. The unit was sampled repeatedly three times during the six months following the flood event, and showed that manganese oxides were reduced at a rate of 1.8 mmol m−2 d−1, whereas the iron oxide concentration did not vary substantially.The second flood unit was composed of darker sediment, rich in organic carbon and reactive manganese oxides. The first step of OM degradation was enhanced within this dark deposit with a high release of dissolved organic carbon (DOC). A peak in Mn2+ concentration was also measured in association with the peak in reactive manganese oxides, also showing the rapid reduction of manganese after an input of fresh reactive oxides, and its potential increased release into the water column. Finally, a peak in nitrate concentration appeared in the sediment porewater within this anoxic organic/manganese-rich layer, likely resulting from the anaerobic oxidation of ammonium by manganese oxides.

16-Year fertilization changes the dynamics of soil oxidizable organic carbon fractions and the stability of soil organic carbon in soybean-corn agroecosystem

Oxidizable organic carbon is a valuable indicator of soil quality, early changes in soil organic carbon (SOC) content, and changes in stabilities of SOC induced by soil fertilization practices. To improve SOC accumulation under soybean-corn cropping system in flat farmland on the Loess Plateau, we examined the effects of nine fertilization treatments [bare land (BL), control (CK), nitrogen (N), phosphorus (P), N + P (NP), manure (M), M + N (MN), M + P (MP), M + N + P (MNP)] on dynamics of SOC and four fractions of oxidizable organic carbon (OC) [very labile (CVL), labile (CL), less labile (CLL) and recalcitrant (CNL)], and stability of SOC over the period of 1997 to 2013. Although SOC content in treatments without fertilization or with inorganic fertilization remained relatively stable between 1997 and 2013, long-term no fertilization or inorganic fertilization caused a depletion of the very labile C (CVL) fraction and increased the stability of SOC. Long-term application of manure promoted an accumulation of SOC in the topsoil between 1997 and 2013, mainly by sequestering labile C (CVL and CL) in the 0–20-cm soil layer, and the dynamics of SOC and CVL contents under these treatments fitted a logistic regression model, which decreased the stability of SOC between 2008 and 2013. SOC content in the subsoil (20–40 cm) under cultivation with organic fertilization increased between 1997 and 2006, but then decreased between 2007 and 2013. Organic fertilization increased CVL and CL contents in the 20–40-cm layer between 1997 and 2010, but then decreased them between 2010 and 2013, and increased the stability of SOC between 2011 and 2013. Our findings indicated that manure fertilization was more effective in promoting SOC enrichment of the soil surface layers by increasing CVL, relative to inorganic fertilization and no fertilization, whereas long-term manure fertilization was associated with a risk of decreasing labile carbon in the 20–40-cm layer and the stability of SOC in the 0–20-cm layer. Manure fertilizer should thus be used cautiously in farmland on the Loess Plateau to guarantee long-term soil carbon stock.

Characteristics of soil organic carbon and its fractions in subtropical evergreen broad-leaved forests along an urbanization gradient.

Subtropical evergreen broad-leaved forests were selected along an urban (Guangzhou) - suburban (Dinghushan) - rural (Huaiji) gradient in the Pearl River Delta, from which soil samples in different layers were collected. The changes in total organic carbon (TOC), recalcitrant organic carbon (ROC), and active organic carbon (AOC) including readily oxidizable organic carbon (ROOC), microbial biomass carbon (MBC), and water-soluble organic carbon (WSOC) of samples were examined along this urbanization gradient to reveal the influence of urbanization on forest soil organic carbon. Results showed that no significant differences in both TOC and ROC contents were observed in 0-5 cm soil layer along the gradient. In 5-60 cm soil layer, the TOC content was significantly higher in the rural forest than that in the suburban and urban forests, the ROC content was the highest in the suburban forest and no significant difference was observed between the urban and rural forests. The ROOC content was significantly lower in the suburban forest than in the rural (0-60 cm soil layer) and urban (0-10 cm soil layer) forests. The MBC content was significantly lower in the urban forest than that in the suburban and rural forests. The suburban forest had significantly lower WSOC than the urban forest (0-10 cm soil layer). In 0-20 cm layer, the percentage of AOC to TOC of the urban and rural forests was significantly higher than those of the suburban forest, while the percentage of ROC to TOC was the lowest in the rural forest. The significant difference in the percentage of ROC to TOC was only observed in 5-10 cm depth layer between the suburban and urban forests. The results indicated that urbanization increased the active components of soil organic carbon and reduced the stable ones, which could be detrimental to organic carbon accumulation in soils. The rural forest soils were more sensitive to the urbanization.

In situ and ex situ bioremediation of seleniferous soils from northwestern India

Selenium (Se) toxicity or deficiency disorders are chiefly associated with Se concentration and speciation in soils. Elevated soil Se content may lead to contamination of water bodies and groundwaters due to the leaching caused by rainfall and irrigation. This study is focused on Se removal by in situ (biostimulation and bioaugmentation) and ex situ (soil washing) bioremediation as well as on its recovery. In this research, in situ bioremediation of Se-rich soil collected from rice fields in Ludhiana, Northwest India was studied in microcosms. The effect of biostimulation was determined by amending soil with different organic sources (fermentable, non-fermentable, and non-hydrolysable electron donors). The effect of bioaugmentation was determined by adding anaerobic granular sludge to the microcosms. With regard to ex situ bioremediation, the Se-rich soil was leached with water and the resulting leachate was biologically treated in an upflow anaerobic sludge blanket (UASB) reactor using lactate as electron donor. The UASB reactor was operated for 78 days in different conditions of lactate (electron donor) dosing to achieve maximum Se removal and recovery as elemental Se(0) on the granular sludge. The effluent of the UASB reactor was regularly analyzed to determine Se removal efficiencies. The effect of biostimulation and bioaugmentation showed no significant difference in terms of Se reduction profiles in the microcosms. This suggested that the indigenous Se-reducing microorganisms and oxidizable organic carbon present in the soil are sufficient for in situ soil bioremediation. During treatment of soil leachate in the UASB reactor, 90% Se removal was achieved irrespective of the lactate dosing and mineral salt medium composition of the reactor influent. Analysis of the granular sludge using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS) and powder X-ray diffraction (P-XRD) confirmed the presence of elemental Se on the granular sludge. The total Se concentration in the anaerobic granular sludge amounted to 43.5 (± 0.7) μg Se per gram of granular sludge. In situ bioremediation achieved Se reduction in the Se-rich soil investigated. However, risk of Se re-oxidation and leaching into groundwater after in situ remediation cannot be disregarded. In contrast, during ex situ treatment, effluent from the UASB reactor contained less than the USEPA guideline value 5 μg L−1 Se. This study showed biological treatment of Se-rich soils is suitable for cleaning the soil, Se recovery, and environmentally acceptable effluent discharge of the soil washing leachate treatment.

The effect of the supporting electrolyte on the electrooxidation of enrofloxacin using a flow cell with a BDD anode: Kinetics and follow-up of oxidation intermediates and antimicrobial activity

The role of the supporting electrolyte – SE (Na2SO4; NaCl; Na2CO3; NaNO3; Na3PO4 – 0.1 M ionic strength) in the galvanostatic (10 mA cm−2) electrochemical degradation of the fluoroquinolone antibiotic enrofloxacin (ENRO; 100 mg L−1) using a filter-press flow cell with a boron-doped diamond anode was investigated (flow rate, solution volume, and temperature were kept fixed at 420 L h−1, 1.0 L, and 25 °C, respectively). The electrochemical degradation performance with the different SEs was assessed by following up [ENRO], total organic carbon concentration (TOC), oxidation intermediates (detected by LC and LC–QqTOF), and antimicrobial activity towards Escherichia coli as the electrolyses progressed. With NaCl as SE, complete removal of ENRO was attained ∼10 times faster than with the other salts. The determination of terminal oxidation intermediates (short-chain carboxylic acids) produced during the electrolyses allowed concluding that their nature and number is indeed affected by the salt used as SE, most probably due to distinct electrogenerated oxidants. With NaCl, the antimicrobial activity of the electrolyzed solution decreased gradually (to ∼20%) from 8 to 16 h of electrolysis due to the cleavage of the fluoroquinolone structure. On the other hand, with Na2SO4, Na2CO3 and NaNO3 as SEs the growth of Escherichia coli cells was observed only after ∼14 h, whereas it was completely inhibited with Na3PO4. Clearly, the electrooxidation and mineralization of ENRO is strongly affected by the SEs used, which determine the degradation mechanism and, consequently, the removal rates of the solution's organic load and antimicrobial activity.

The Effects of Rice Straw and Biochar Applications on the Microbial Community in a Soil with a History of Continuous Tomato Planting History

Soil microbial abundance and diversity change constantly in continuous cropping systems, resulting in the prevalence of soil-borne pathogens and a decline in crop yield in solar greenhouses. To investigate the effects of rice straw and biochar on soil microbial abundance and diversity in soils with a history of continuous planting, three treatments were examined: mixed rice straw and biochar addition (RC), rice straw addition (R), and biochar addition (C). The amount of C added in each treatment group was 3.78 g kg−1 soil. Soil without rice straw and biochar addition was treated as a control (CK). Results showed that RC treatment significantly increased soil pH, available nitrogen (AN), available phosphorus (AP), and potassium (AK) by 40.3%, 157.2%, and 24.2%, respectively, as compared to the CK soil. The amount of soil labile organic carbon (LOC), including readily oxidizable organic carbon (ROC), dissolved organic carbon (DOC), and light fraction organic carbon (LFOC), was significantly greater in the RC, R, and C treatment groups as compared to CK soil. LOC levels with RC treatment were higher than with the other treatments. Both rice straw and biochar addition significantly increased bacterial and total microbial abundance, whereas rice straw but not biochar addition improved soil microbial carbon metabolism and diversity. Thus, the significant effects of rice straw and biochar on soil microbial carbon metabolism and diversity were attributed to the quantity of DOC in the treatments. Therefore, our results indicated that soil microbial diversity is directly associated with DOC. Based on the results of this study, mixed rice straw and biochar addition, rather than their application individually, might be key to restoring degraded soil.

Changes in soil organic carbon fractions in response to different tillage practices under a wheat‐maize double cropping system

AbstractTo understand the turnover of soil organic carbon (SOC) and the improvement of soil quality in response to tillage practices, it is important to identify changes in labile SOC fractions, for example, permanganate oxidizable organic carbon (POxC) and particulate organic carbon (POC). Five tillage treatments were initially undertaken in a winter wheat (Triticum aestivum L., mid‐October to early‐June)–summer maize (Zea mays L., mid‐June to early‐October) system in the North China Plain in 2008 with changes being examined in 2012–2013. These treatments included plough tillage with residue removed, plough tillage with residue incorporation, no tillage with residue mulching, subsoiling with residue incorporation, and rotary tillage (tillage with a rotary tiller) with residue incorporation for the winter wheat season; summer maize was only managed with the NTM treatment. The greatest POxC and POC concentrations at the 0–5‐cm depth were observed under RTR and NTM treatments (p < .05), respectively. Both STR and RTR recorded larger POxC and POC concentrations at the 5–10‐cm depth (p < .05). Both POxC and POC concentrations for STR treatment were significantly higher than those under RTR, NTM, and PT0 treatments in the 20–50‐cm soil profile. The POC concentrations in each soil layer of 0–30‐cm showed a significant response to residue amount, temperature, and precipitation; and POxC concentrations did not record similar responses. Therefore, subsoiling with residue incorporation could be a potential tillage practice to manage labile SOC pool in top soil (0–50‐cm) in the North China Plain region.

Microbial oxidation of lithospheric organic carbon in rapidly eroding tropical mountain soils

Lithospheric organic carbon ("petrogenic"; OCpetro) 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 OCpetro 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 OCpetro 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.

The effect of different operational parameters on the electrooxidation of indigo carmine on Ti/IrO2-SnO2-Sb2O3

The electrochemical oxidation of indigo carmine (IC) is evaluated on a Dimensionally Stable Anode (DSA) made up of Sb2O3 doped Ti/IrO2-SnO2 (Ir-Sn-Sb). Particular efforts are devoted to investigate different electrochemical parameters including current density, IC concentration, initial pH of the solution, and the content of multiple ions (Cl−, SO4−2 or HCO3−) typically found in textile dyeing wastewater. The IC removal efficiency is calculated using the following physicochemical parameters: color removal (611 nm), Chemical Oxygen Demand (COD mg L−1 O2), Total Organic Carbon (TOC mg L−1C) and Average Oxidation State (AOS). The results reveal that IC oxidation is enhanced in the presence of chlorides due to the action of active chlorine species (Cl2-active) electrogenerated on the anode surface. In this medium, the initial oxidation rate of IC was higher at pH 2 than any other value including natural pH of 6.62 and 10. Both the increase of the chloride concentration in the electrolyte and the rise of current density expedite the color removal with a lower energetic consumption. Optimum treatment conditions were found using 0.25 mol L−1 NaCl at pH 2 and applying 9.375 mA cm−2. Under these conditions, a total color removal is achieved, along with 77.5% COD, 24% TOC and the rise of AOS value to 2.9. High performance liquid chromatography analysis and mass spectrometry provide insights concerning the first degradation stages, involving the attacks of electrogenerated HClO in the double bond CC chromophore group of IC, thus, generating isatin-5-sulfonic acid (m/z 226) as the main reaction intermediate. This compound is subsequently removed to form aliphatic byproducts. COD removal and the final AOS value suggest that the electrochemical process transforms the IC to biodegradable intermediates, which can be eventually eliminated in a subsequent biological treatment.

Fractionnement Géochimique Des Eléments Traces Métalliques (Etm) Dans Les Sédiments Du Delta De L’ouémé Au Bénin

Due to the inherent damages of trace elements to living organisms, the amount of bio available metal is considered to be a quantity that conditions the becoming of aquatic ecosystems. The aim of this work is to evaluate the proportion of Pb, Cu and Cd that are biologically available in the superficial sediments of the Ouémé estuary as well as the influence of environmental factors on the becoming of these metals. Fractionation of the metals was performed according to the sequential extraction method and their measurement was done by inductively coupled plasma mass spectrometer (ICP-MS). Physicochemical parameters evaluated are: granulometry, pH, cation exchange capacity (CEC), organic carbon (Corg), iron, aluminum and calcium oxides (Fe2O3, Al2O3 and CaO). Risk indices related to metal fractionation were evaluated followed by statistical processing in R 3.3.2. It appears that: 39.44% of the Cd are preferentially bound to the exchangeable fraction, 37.25% of the Pb are for the reducible fraction and 47.47% of the Cu for the oxidizable fraction. Risk levels are in the low to very high range. The richness of materials is revealed as a factor limiting the bioavailability of metals while CaO facilitates the bioavailability in high risk sites. Liquid and solid wastes from the Dantokpa market are the potential sources of metals.

The contributions of underground-nesting ants to CO2 emission from tropical forest soils vary with species

The aboveground ant nests are admitted as hot spots for CO2 emissions which increase heterogeneity of soil carbon (C) flux in forest ecosystems. However, little is known about effects of underground-nesting ant species on C emissions in tropical forests, where the ants have high diversity and abundance. In this study, we chose three underground-nesting ant species with different feeding-behaviors (Pheidole capellini - predominantly honeydew harvester, Odontoponera transversa - predominantly predator, and Pheidologeton affinis - scavenger) to explore their impacts on soil CO2 emission in Xishuangbanna tropical forest, China. We observed a pronounced effect of ants on CO2 emission, and the effect varied with ant species. The mean CO2 emissions were 2.4 times higher in P. capellini nests than in the reference soils, while those in nests of O. transversa and P. affinis were 2.0 and 1.6 folds, respectively. The contribution of total CO2 flux from nests of three ant species comprised 0.01–0.54% of total annual CO2 efflux from the forest floor. The CO2 emission in ant nests and reference soils increased exponentially with soil temperature and water. Soil water was considerably increased by ant nesting, which explained nearly 93–97% of CO2 emissions. However, soil temperature was not significantly different between nests and reference soils, and it only explained about 54–70% of CO2 emission. Ant species differed in increase of soil microbial biomass carbon, total organic carbon, readily oxidizable organic carbon, soil bulk density and pH, which also contributed to a diverse effect on soil CO2 emission. We suggest that the different effects of ant species on C emission may be closely associated with diversity of ant population size, feeding-behaviors and nesting modification on soil microbial biomass carbon, and physicochemical properties (i.e., temperature, moisture, pH, Bulk density, total and readily oxidizable organic carbon) in the tropical forest.

The synergistic effect of calcium on organic carbon sequestration to ferrihydrite

Sequestration of organic carbon (OC) in environmental systems is critical to mitigating climate change. Organo-mineral associations, especially those with iron (Fe) oxides, drive the chemistry of OC sequestration and stability in soils. Short-range-ordered Fe oxides, such as ferrihydrite, demonstrate a high affinity for OC in binary systems. Calcium commonly co-associates with OC and Fe oxides in soils, though the bonding mechanism (e.g., cation bridging) and implications of the co-association for OC sequestration remain unresolved. We explored the effect of calcium (Ca2+) on the sorption of dissolved OC to 2-line ferrihydrite. Sorption experiments were conducted between leaf litter-extractable OC and ferrihydrite at pH 4 to 9 with different initial C/Fe molar ratios and Ca2+ concentrations. The extent of OC sorption to ferrihydrite in the presence of Ca2+ increased across all tested pH values, especially at pH ≥ 7. Sorbed OC concentration at pH 9 increased from 8.72 ± 0.16 to 13.3 ± 0.20 mmol OC g−1 ferrihydrite between treatments of no added Ca2+ and 30 mM Ca2+ addition. Batch experiments were paired with spectroscopic studies to probe the speciation of sorbed OC and elucidate the sorption mechanism. ATR-FTIR spectroscopy analysis revealed that carboxylic functional moieties were the primary sorbed OC species that were preferentially bound to ferrihydrite and suggested an increase in Fe-carboxylate ligand exchange in the presence of Ca at pH 9. Results from batch to spectroscopic experiments provide significant evidence for the enhancement of dissolved OC sequestration to 2-line ferrihydrite and suggest the formation of Fe–Ca-OC ternary complexes. Findings of this research will inform modeling of environmental C cycling and have the potential to influence strategies for managing land to minimize OM stabilization.

Genomic insights into metabolic potentials of two simultaneous aerobic denitrification and phosphorus removal bacteria, Achromobacter sp. GAD3 and Agrobacterium sp. LAD9.

Bacteria capable of simultaneous aerobic denitrification and phosphorus removal (SADPR) are promising for the establishment of novel one-stage wastewater treatment systems. Nevertheless, insights into the metabolic potential of SADPR-related bacteria are limited. Here, comprehensive metabolic models of two efficient SADPR bacteria, Achromobacter sp. GAD3 and Agrobacterium sp. LAD9, were obtained for the first time by high-throughput genome sequencing. With succinate as the preferred carbon source, both strains employed a complete TCA cycle as the major carbon metabolism for potentials of various organic acids and complex carbon oxidation. Complete and truncated aerobic denitrification routes were confirmed in GAD3 and LAD9, respectively, facilitated by all the major components of the electron transfer chain via oxidative phosphorylation. Comparative genome analysis revealed distinctive ecological niches involved in denitrification among different phylogenetic clades within Achromobacter and Agrobacterium. Excellent phosphorus removal capacities were contributed by inorganic phosphate uptake, polyphosphate synthesis and phosphonate metabolism. Additionally, the physiology of GAD3/LAD9 is different from that displayed by most available polyphosphate accumulating organisms, and reveals both strains to be more versatile, carrying out potentials for diverse organics degradation and outstanding SADPR capacity within a single organism. The functional exploration of SADPR bacteria broadens their significant prospects for application in concurrent aerobic carbon and nutrient removal.

Effects of water and salinity regulation measures on soil carbon sequestration in coastal wetlands of the Yellow River Delta

Water and salinity regulation measures have been widely taken to restore the ecological structures and functions of degraded coastal wetlands. To investigate the effects of different water and salinity regulation measures on soil carbon stocks in coastal wetlands, soil samples were collected to a depth of 50cm in four types of wetlands (i.e., restored tidal salt marshes (RTSM, covered with Suaeda salsa) and degraded tidal salt marshes (DTSM, bare land); freshwater restored wetlands (FRW) and degraded wetlands without freshwater inputs (DWFI), covered with Phragmites australis) during the period from August to October in 2015 in the Yellow River Delta, China. Our results showed that the mean values of total carbon (TC), soil organic carbon (SOC), readily oxidizable organic carbon (ROOC) and dissolved organic carbon (DOC) were higher in restored wetlands (e.g., RTSM and FRW) than those in degraded wetlands (e.g., DTSM and DWFI). Along the whole soil profile, TC, SOC, ROOC and DOC were higher in RTSM soils than those in DTSM soils except for TC and SOC in the 0–10cm soils and DOC in the 40–50cm soils. FRW soils contained higher TC, SOC, ROOC and DOC than DWFI except for DOC in the 0–10cm soils. Soil TC density (TCD), SOC density (SOCD), ROOC density (ROOCD) and DOC density (DOCD) in the top 50cm soils in restored wetlands were higher compared with degraded wetlands. Multivariate analysis showed that soil carbon was significantly influenced by EC, soil base cations and anions (e.g., K+, Ca2+, Cl− and SO42−), pH, TN, C/N ratio, bulk density (BD) and soil texture (p<0.05). The findings of this study indicated that these two water and salinity regulation measures are effective in increasing soil carbon stocks of coastal wetlands.

Interactive effects of rice-residue biochar and N-fertilizer on soil functions and crop biomass in contrasting soils

There is limited understanding of the effects of rice residue biochar, particularly when applied in combination with nitrogen (N) fertilizer on soil fertility, soil C sequestration and crop productivity. A one-year pot experiment was established to examine effects of rice residue biochar (0, 10, 20 and 40 t ha-1) and N (0, 60, 90, 120 and 150 kg N ha-1) in soils with contrasting texture (loamy sand and sandy clay loam) in a wheat(maize cropping sequence. Biochar was only applied once before sowing wheat. Biochar alone or in combination with N did not significantly increase wheat biomass in both soils, whereas biomass of maize (next crop) was significantly increased from the residual effect of biochar, alone or in combination with N fertilizer. In both soils, electrical conductivity (EC) and pH, oxidisable organic carbon (OC), microbial biomass carbon (MBC), dissolved organic carbon (DOC) and available nutrients (NPK) increased with increasing rates of biochar addition. However, addition of N with biochar (cf. biochar alone) did not change pH and oxidisable OC values but increased EC significantly. After one year, the soil organic carbon (SOC) stocks increased beyond the input of biochar-C, that is, by 0.1-2.1 t ha-1 and 1.8-4.8 t ha-1 in loamy sand and sandy clay loam, respectively, across all treatments. It may be concluded that the potential benefits of rice residue biochar to soil functions and crop production may encourage growers to minimise open field burning of straw, which is a common practice in the region.

Corrigendum to: Effects of nitrogen addition on soil oxidisable organic carbon fractions in the rhizospheric and bulk soils of Chinese pines in north-western China

Increased atmospheric nitrogen (N) deposition caused by human activities has potentially important effects on ecosystem carbon (C) dynamics and different effects on C fractions with different stabilities and chemical compositions. A better understanding of the responses of different C fractions to N addition is vital for maintaining soil quality and protecting vegetation. In order to investigate the differential effects of N addition on total soil organic carbon (SOC) and four SOC fractions with increasing degrees of oxidisability in Pinus tabuliformis rhizospheric and bulk soils, a 6-year pot experiment was performed testing the effects of the addition of N at rates of 2.8, 5.6, 11.2, 22.4 and 44.8g m–2 year–1 compared with a control (CK) group (no N addition). Addition of N addition had significant (P–2 year–1. Low rates (N2.8–N5.6) of N addition considerably increased C4 and the ratio of C4 to TOC in the rhizosphere, whereas addition of high rates (N11.2–N44.8) of N decreased these parameters. The responses of C1 and C4 in the bulk soil to N addition were opposite. The SOC fraction was significantly higher in the rhizosphere than in the bulk soil, indicating large rhizospheric effects. However, increased N addition weakened these effects. These findings suggest that low rates (N2.8–N5.6) of N addition stabilise SOC against chemical and biological degradation, whereas increased rates of N addition increase the lability of SOC in the bulk soil. Thus, the rhizosphere plays a vital role in soil carbon stability and sequestration in response to N addition.

Soil carbon pools under long-term rice-wheat cropping system in Inceptisols of Indian Himalayas

ABSTRACTKnowledge about soil organic carbon (SOC) stock and its allocation into different pools is important for global food and environmental security. Accordingly, an attempt is made in the present study to investigate into the dynamics of SOC pools i.e. total soil organic carbon (TOC), oxidisable organic carbon (OC) and its different fractions viz. very labile (CVL), labile (CL), less labile (CLL) and non-labile (CNL) in soils under a 26 years old long-term experiment with rice (Oryza sativa L) – wheat (Triticum aestivum L) cropping system on Inceptisols under humid agro-climatic region of India with different soil management practices (control, 100% recommended dose of NPK, and 50% recommended dose of NPK + 50% N through farmyard manure (FYM). Of the several pools analyzed, a higher proportion of C was found in labile pool followed by very labile, non-labile, and less labile ones constituting about 46, 26.5, 20 and 7.3% of the total organic C at surface soil. The NPK+FYM treatment was found to have higher SOC pools, lability index (LI), recalcitrance indices and stratification ratio as compared to others. Results indicated that balanced fertilization with inorganic and organics is important for maintaining overall sustainability of the rice-wheat system.

Response of surface albedo and soil carbon dioxide fluxes to biochar amendment in farmland

Understanding the effect of biochar on surface albedo and soil CO2 fluxes is a crucial issue in evaluating the impact of biochar on carbon sequestration and greenhouse gas mitigation. In this study, we consider the following research questions: (1) Under bare soil and crop coverage conditions, do different dosages of biochar decrease the surface albedo? (2) How does the application of biochar affect soil CO2 fluxes? (3) What are the influencing factors of surface albedo and soil CO2 fluxes after biochar is applied? We examined the influence of biochar applications on farmland on the surface albedo, soil CO2 flux, soil temperature, soil moisture, and soil organic carbon fractions over a period of 15 months. There are six treatments (CK+, CK−, BC5+, BC5−, BC45+, and BC45−) in this study, and three biochar application rates, which are as follows: 0 t ha−1 year−1 (CK), 5 t ha−1 year−1 (BC5), and 45 t ha−1 year−1 (BC45) of biochar, and each application is rated with two crop coverage conditions, a wheat-maize crop rotation (+) and bare soil (−). We found that in the early stage of crop growth, the surface albedo of BC45+ and BC5+ were decreased significantly compared with the control treatment (P < 0.05). As the crop canopy structures developed, the surface albedo reduction weakened or even disappeared. Under the bare soil condition, the surface albedos of BC45− and BC5− was decreased significantly in most of the measurements (P < 0.05). The soil CO2 fluxes of the biochar treatments were increased significantly (P < 0.05). However, the growth rates of the soil CO2 fluxes of BC45+, BC5+, BC45−, and BC5− gradually decreased with time. The increase in the CO2 emissions of biochar treatments may be due to mineralization of the readily oxidizable organic carbon (e.g., water-soluble organic carbon) in the biochar-soil system. Adding biochar to the soil reduced the sensitivity of the soil respiration to temperature changes. The leaf area index is one of the factors that affects the surface albedo. The surface albedo did not decrease proportionally with the increase in biochar application. Readily oxidizable organic carbon played an important role in the soil CO2 emissions. The reduction of surface albedo caused by the biochar has no direct effect on soil CO2 fluxes. The findings were helpful in evaluating the effects of adding biochar to soil and its consequences for C sequestration in agricultural soils.

Carbon Inputs From Riparian Vegetation Limit Oxidation of Physically Bound Organic Carbon Via Biochemical and Thermodynamic Processes

AbstractIn light of increasing terrestrial carbon (C) transport across aquatic boundaries, the mechanisms governing organic carbon (OC) oxidation along terrestrial‐aquatic interfaces are crucial to future climate predictions. Here we investigate the biochemistry, metabolic pathways, and thermodynamics corresponding to OC oxidation in the Columbia River corridor using ultrahigh‐resolution C characterization. We leverage natural vegetative differences to encompass variation in terrestrial C inputs. Our results suggest that decreases in terrestrial C deposition associated with diminished riparian vegetation induce oxidation of physically bound OC. We also find that contrasting metabolic pathways oxidize OC in the presence and absence of vegetation and—in direct conflict with the “priming” concept—that inputs of water‐soluble and thermodynamically favorable terrestrial OC protect bound‐OC from oxidation. In both environments, the most thermodynamically favorable compounds appear to be preferentially oxidized regardless of which OC pool microbiomes metabolize. In turn, we suggest that the extent of riparian vegetation causes sediment microbiomes to locally adapt to oxidize a particular pool of OC but that common thermodynamic principles govern the oxidation of each pool (i.e., water‐soluble or physically bound). Finally, we propose a mechanistic conceptualization of OC oxidation along terrestrial‐aquatic interfaces that can be used to model heterogeneous patterns of OC loss under changing land cover distributions.