Organic Carbon Mineralization Research Articles

Effects of Microbial-Mineral Interactions on Organic Carbon Stabilization in a Ponderosa Pine Root Zone: A Micro-Scale Approach

Soil microbial communities affect the formation of micro-scale mineral-associated organic matter (MAOM) where complex processes, including adhesion, aggregate formation, microbial mineral weathering and soil organic matter stabilization occur in a narrow zone of large biogeochemical gradients. Here we designed a field study to examine carbon stabilization mechanisms by using in-growth mesh bags containing biotite that were placed in a ponderosa pine root zone for 6 months and compared to the surrounding bulk soil. We sought to determine the composition of the microbial community in the mesh bags compared to the surrounding soils, analyze the direct interactions between microbes and biotite, and finally identify the nature of the newly formed MAOM within the mesh-bags. Our results revealed that minerals in the mesh bags were colonized by a microbial community that produced organic matter in situ. The 16S rRNA gene sequencing and ITS2 region characterization showed phylogenetic similarity between the mesh bag and bulk soil archaea/bacteria and fungi microbiomes, with significant differences in alpha- and beta-diversity and species abundances. Organic matter pools in the mesh bags, analyzed by Fourier transform ion cyclotron resonance mass spectrometry, contained protein- (peptides) and lipid-like compounds while the bulk soil OM was comprised of lignin-like and carboxyl-rich alicyclic molecules. These results support that the newly formed biotite associated organic compounds have a microbial signature in the mesh bags. High-resolution electron microscopy documented strongly adhered organic compounds to biotite surfaces, formation of microaggregates, elemental uptake at the microbe (organic matter)-mineral interface, and distortion of biotite layers. Overall, this study shows the direct and indirect involvement of soil microbial communities from the root zone of ponderosa pine in the formation of MAOM, soil organic carbon stabilization, microaggregation, and mineral weathering at micro- and nano-scales.

Towards passive bioremediation of dye-bearing effluents using hydrous ferric oxide wastes: Mechanisms, products and microbiology

A novel, circular economy-inspired approach for the “passive” (non-powered and reagent-free) treatment of dye-bearing effluent is presented. The treatment utilises the biogeochemical interaction of dye-bearing wastewater with hydrous ferric oxide (HFO) bearing sludges. The work presented demonstrates for the first time the reuse of HFO-rich waste sludges from potable water and mine water treatment. The waste was used directly without modification or reagent addition, as media/substrate in simple flow-through reactors for the decolourisation and biodegradation of methyl orange (MO) and mixed dyes textile effluent. Three phases of exploratory proof of concept work were undertaken. Columns containing HFO sludges were challenged with solution of MO, and MO amended with glycerol (Phase I), MO in a synthetic textile effluent recipe (Phase II), and real mixed textile effluent containing a mixture of dyes (Phase III). After an initial lag period extensive decolourisation of dye was observed in all cases at rates comparable with pure strains and engineered bioreactor processes, with evidence of biodegradation beyond simple cleavage of the mono azo chromophore and mineralisation. The microbiology of the initial sludge samples in both cases exhibited a diverse range of iron oxidising and reducing bacteria. However, post experiment the microbiology of sludge evolved from being dominated by Proteobacteria to being dominated by Firmicutes. Distinct changes in the microbial community structure were observed in post-treatment MWTS and WTWS where genera capable of iron and sulphate reduction and/or aromatic amine degradation were identified. Average nitrogen removal rates for the columns ranged from 27.8 to 194 g/m3/day which is higher than engineered sequential anaerobic-aerobic bioreactor. Postulated mechanisms for the fast anaerobic decolourisation, biodegradation, and mineralisation of the dyes (as well nitrogen transformations) include various direct and indirect enzymatic and metabolic reactions, as well as reductive attack by continuously regenerated reductants such as Fe(II), HFO bound Fe(II), FeS, and HS−. The ability of iron reducers to degrade aromatic rings is also considered important in the further biodegradation and complete mineralisation of organic carbon. The study reveals that abundant and ubiquitous HFO-rich waste sludges, can be used without amendment, as a substrate in simple flow-through bioremediation system for the decolourisation and partial biodegradation of dyes in textile effluent.

Soil Organic Carbon Mineralization and Its Temperature Sensitivity under Different Substrate Levels in the Mollisols of Northeast China.

Soil organic carbon (SOC) mineralization plays an important role in global climate change. Temperature affects SOC mineralization, and its effect can be limited by the substrate available. However, knowledge of the effects of temperature and substrate quality on SOC mineralization in the Mollisols of Northeast China is still lacking. In this study, based on a spatial transplant experiment, we conducted a 73-day incubation to examine the effects of temperature on SOC mineralization and its temperature sensitivity under different carbon levels. We found that the SOC content, incubation temperature and their interaction had significant effects on SOC mineralization. A higher SOC content and higher incubation temperature resulted in higher SOC mineralization. The temperature sensitivity of SOC mineralization was affected by the substrate quality. The temperature sensitivity of SOC mineralization, showed a downward trend during the incubation period, and the range of variation in the Q10 declined with the increment in the SOC content. The study suggested that there was a higher SOC mineralization in high levels of substrate carbon when the temperature increased. Further, SOC mineralization under higher SOC contents was more sensitive to temperature changes. Our study provides vital information for SOC turnover and the CO2 sequestration capacity under global warming in the Mollisols of Northeast China and other black soil regions of the world.

Tree species mixing enhances rhizosphere soil organic carbon mineralization of conifers in subtropical plantations

Tree species mixing is a prevalent practice to improve soil quality in monoculture plantations and the rhizosphere soil organic carbon (SOC) dynamics of conifers will be affected by mixing the species with broad-leaved trees; however, the influence characteristics and underlying mechanism of mixing on rhizosphere SOC mineralization remain elusive. Herein, the rhizosphere soils of two conifers (Pinus massoniana and Pinus elliottii) from pure and mixed plantations were incubated for 50 days. Bacterial communities were investigated by high-throughput sequencing and qPCR of the 16S rRNA gene. The SOC quality represented by carbon functional groups was analyzed using a Fourier transform infrared spectrometer. A higher rhizosphere SOC quality of conifers, particularly the lower ratios of aromatic/aliphatic compounds and (aromatic + aliphatic compounds)/polysaccharide, was found in the mixed plantation compared to the pure plantation. Mixing increased the relative abundance of the conifer rhizosphere copiotrophic bacteria (Proteobacteria and Bacteroidetes) and led to an increase in the bacterial copiotroph:oligotroph ratio. The redundancy analysis showed that the aromatic/aliphatic compound ratio was the predominant factor that significantly affected the soil bacterial communities. The rhizosphere SOC mineralization rate increased after mixing and had a positive relationship with copiotrophic bacteria and the bacterial copiotroph:oligotroph ratio. Our analyses indicate that planting broad-leaved trees in coniferous plantations increases organic carbon mineralization from the rhizosphere soil of conifers and provide potential driving patterns of SOC mineralization related to SOC quality and bacterial life strategy.

COMPARISON OF C AND N MINERALIZATION AND METAGENOME ANALYSIS OF RHIZOSPHERE SOILS BELONGING TO DIFFERENT Colchicum L. SPECIES

This study is aimed at determining the characteristics and microbiota of soil upon which some Turkish Colchicum (Colchicaceae) species naturally grows. For this aim the rhizosphere soil samples of Colchicum balansae Planch., Colchicum triphyllum Kunze and Colchicum variegatum L. were analysed in this research. The carbon mineralization rate of C. balansae soil at p<0.05 is significantly different from that of the other two soils. In terms of nitrogen mineralization, significant difference exists between all the three soils (p<0.001). Colchicum variegatum rhizosphere was found to have the highest bacterial diversity. The results revealed that 254 bacterial species were common to the three rhizosphere soils, 35.60% of the bacterial species were unique to C. variegatum soil while 21.89% and 22.67% of the bacterial species were unique to C. balansae and C. triphyllum soil respectively. It was found that C. variegatum and C. balansae collected from areas close to each other had the highest number of common bacterial species, while C. triphyllum from the distant region shared 75 with C. variegatum and 19 with C. balansae. Metagenomics analysis reveals that in the rhizophere of C. variegatum, C. balansae and C. triphyllum, Actinobacteria is dominant at phylum level. Likewise, in C. variegatum soil, Nitrosocosmicus and halophilic Halobacter were found to be the dominant archaea. In the soils of C. triphyllum and C. balansae Saccharomycetales were detected, while Cryptococcus neoformans var. grubii H99 was exclusively detected in C. balansae soil. Significant difference (p<0.05) was observed in C. variegatum rhizosphere soil in terms of organic carbon (C%) and carbon mineralization from the other two soil samples. Significant differences were observed in all three soils in terms of nitrogen content, and the C. triphyllum rhizosphere soil was significantly different from the others in terms of available phosphorus content (p<0.05). This study showed that biological as well as the physico-chemical properties of the rhizosphere soil regulate soil microbial diversity and density and by extension influences their activity which evidently manifests itself in carbon and nitrogen mineralisation.

Microbial response to multiple-level addition of grass organic matter in lake sediments with different salinity.

Water surface expansion of saline lakes usually causes the inundation of surrounding grassland, leading to the increase of terrestrial grass organic matter (OM) input to the lakes and the decrease of lake salinity. However, the influence of terrestrial grass OM input increase and salinity decrease on organic carbon mineralization and microbial community composition remains unknown in saline lakes. Here, microbial mineralization of terrestrial grass (Achnatherum splendens) OM at different quantity levels in lake sediments with different salinity was investigated by performing microcosm experiments. The results showed that the CO2 production rates increased with the increase of grass OM supply in the studied sediments with different salinity, which may be driven by certain microbial groups (e.g. Bacteroidota, Firmicutes, and Ascomycota). The increase of grass OM supply reduced the richness of prokaryotic community, which will decrease the size and complexity of the studied microbial networks, but increase the interaction between prokaryotic and fungal taxa. Taken together, our results suggest that the increase of terrestrial grass OM input caused by lake expansion would enhance the mineralization of organic carbon and affect the community composition and interactions of related microorganisms in lake sediments with different salinity.

Stoichiometric regulation of priming effects and soil carbon balance by microbial life strategies

Carbon and nutrient inputs are required to stimulate the formation and mineralization of soil organic carbon (SOC) through processes related to microbial growth and priming effects (PEs). PEs are thought to affect microbial life strategies, however, the mechanisms underlying their role in SOC formation and microbial dynamics remain largely unknown, particularly in paddy soils. Here, we examined the underlying strategies and response mechanisms of microorganisms in regulating PEs and C accumulation in flooded paddy soil. Levels and stoichiometric ratios of resources were evaluated over a 60-day incubation period. Low (equivalent to 50% soil microbial biomass C [MBC]) and high (500% MBC) doses of 13C-labeled glucose were added to the soil, along with mineral N, P, and S (NPS) fertilizers at five concentrations. Glucose mineralization increased linearly with NPS concentration under both low and high glucose inputs. However, glucose addition without nutrients induced the preferential microbial utilization of the readily available C, leading to negative PEs. Under high-glucose input, the intensity of negative PEs increased with increasing NPS addition (PE: from −460 to −710 mg C kg−1 soil). In contrast, under low-glucose inputs, the intensity of positive PEs increased with increasing NPS addition (PE: 60–100 mg C kg−1 soil). High-glucose input with NPS fertilization favored high-yield microbial strategists (Y-strategists), increasing glucose-derived SOC accumulation. This phenomenon was evidenced by the large quantities of 13C detected in microbial biomass and phospholipid fatty acids (PLFAs), increasing the soil net C balance (from 0.76 to 1.2 g C kg−1). In contrast, low levels of glucose and NPS fertilization shifted the microbial community composition toward dominance of resource-acquisition strategists (A-strategists), increasing SOC mineralization. This was evidenced by 13C incorporation into the PLFAs of gram-positive bacteria, increased activity of N- and P-hydrolases, and positive PEs for acquiring C and nutrients from soil organic matter. Consequently, the soil net C balance decreased from 0.31 to 0.01 g C kg−1 soil. In conclusion, high C input (i.e., 500% MBC), particularly alongside hig NPS addition, increases SOC content via negative priming and microbial-derived C accumulation due to the shift toward Y-strategist communities which efficiently utilize resources. This study highlights the importance of mineral fertilization management when incorporating organic supplements in paddy soils to stimulate microbial turnover and C sequestration.

Effects of Organic Fertilizer Replacing Chemical Fertilizer on Organic Carbon Mineralization and Active Organic Carbon in Dryland Yellow Soil

At present, the effect characteristics and mechanism of organic fertilizer replacing chemical fertilizer on organic carbon mineralization and active organic carbon in dryland yellow soil remain unclear. In order to explore the effect of organic fertilizer replacing chemical fertilizer on organic carbon mineralization and active organic carbon in dryland yellow soil, we used soil with no fertilization (CK), only chemical fertilizer (NP), 50% organic fertilizer replacing chemical fertilizer (1/2(NPM)), and 100% organic fertilizer replacing chemical fertilizer (M). We examined the indoor mineralization culture of organic carbon and explored the characteristics of soil organic carbon and the change in active organic carbon under the condition of organic fertilizer replacing chemical fertilizer. The results showed that organic fertilizer replacing chemical fertilizer increased soil pH, organic carbon (SOC), total nitrogen (TN), and C/N. During the culture period, the soil organic carbon mineralization rate of all treatments decreased sharply in the initial stage (2-4 days), decreased slightly in the middle stage (4-20 days), and tended to be stable in the last stage (20-60 days). After fertilization, the cumulative mineralization of soil organic carbon significantly increased by 7.9%-27.7%. Compared with that in the NP treatment, the cumulative mineralization of soil organic carbon decreased by 5.2% in the 1/2(NPM) treatment and increased by 12.2% in the 1/2(NPM) treatment. Before mineralization culture, the substitution of organic fertilizer for chemical fertilizer had no significant effect on soil recalcitrant organic carbon (ROC) but significantly increased the content of microbial biomass carbon (MBC). The content of dissolved organic carbon (DOC) was significantly increased in the 1/2(NPM) treatment and decreased in the M treatment. After 60 days of culture, the content of soil active organic carbon in all treatments decreased compared with the initial content, of which MBC decreased the most (30.6%-41.2%). The accumulated mineralization of organic carbon was significantly positively correlated with soil pH and SOC and significantly positively correlated with the initial value of MBC and the change value before and after culture. To summarize, 100% organic fertilizer replacing chemical fertilizer significantly promoted soil organic carbon mineralization and reduced soil organic carbon stability; 50% organic fertilizer replacing chemical fertilizer inhibited soil organic carbon mineralization, which was beneficial to soil sequestration and fertilization; and 50% organic fertilizer replacing chemical fertilizer significantly increased soil active organic carbon content, and MBC was used as the main carbon source in the process of soil organic carbon mineralization.

Biochar stability and impact on soil organic carbon mineralization depend on biochar processing, aging and soil clay content

The carbon sequestration potential of biochar depends on its stability in the soil and its priming effect on native soil organic carbon mineralization, which could be expected to be in turn affected by biochar processing, aging and soil clay content. This study applied stable carbon isotopes (δ13C) to quantify the mineralization of fresh and aged biochar pyrolyzed at 300, 450, and 600 °C and their priming effects on native soil organic carbon in two types of soils with different clay contents. At the end of the incubation, the total carbon loss of biochar-amended soil was 16–53% lower than that of unamended soil and the lowest carbon loss was found in soils amended with 600 °C biochar. Regardless of soil type, the proportion of biochar-carbon (carbon in the biochar) mineralized decreased with increasing pyrolysis temperature. For fresh biochar, the proportion of carbon mineralized was 13–47% higher in the sandy loam soil than in the sandy clay loam soil at the end of the incubation. However, soil type had a minimal effect on the mineralization proportion of aged biochar-carbon. The dissolved organic carbon increased after fresh and aged biochar was added to the sandy clay loam, but not the sandy loam, suggesting less carbon hydrolysis and solubilization from native soil organic carbon and biochar in the sandy loam soil. Moreover, biochar amendment increased the enzyme activities in sandy clay loam soil and either increased or had no effect on those in sandy loam soil. Fresh biochar had no effect on native soil organic carbon mineralization after it was applied, although a negative priming effect was observed after two−7 wk. For aged biochar, a negative priming effect was found for both soils. These findings demonstrated that biochar was more stable in clayey soils, and biochar produced at higher temperature indeed showed high soil carbon sequestration potential.

Differentiated impacts of the feeding-habits of three ant species on carbon mineralization in tropical forest soils

Ants affect carbon mineralization probably through their modifications on spatiotemporal heterogeneity in soil nutrients. However, it is still unclear whether the impacts of belowground-nesting ants on carbon mineralization varied with species. For this study, three belowground-nesting ants (i.e., honeydew harvester Pheidole capellini, predatory Odontoponera transversa, and saprophagous Pheidologeton affinis) were considered to identify the effects on soil carbon mineralization in the tropical Xishuangbanna (Yunnan, southern China). P. capellini had the greatest carbon mineralization (1.9 times) in the nest soils compared with control soils, followed by O. transversa (1.5 times) and P. affinis (1.3 times). Ants had different modifications on the changes of carbon mineralization as well as soil nutrient availability. The highest increased levels (24.7–298.5%) of carbon and nitrogen pools were observed in P. capellini nests compared with control soils. Soil carbon and nitrogen pools together affected soil carbon mineralization dynamics. Total organic carbon, microbial biomass carbon, and readily oxidizable carbon were the key factors regulating soil organic carbon mineralization, followed by total, ammonium and dissolved nitrogen. Our results suggested that carbon mineralization differed among ant species, which was tightly linked with the effects of different feeding guilds on nutrient availability in tropical forest soils.

The mineralization and sequestration of soil organic carbon in relation to gully erosion

Water erosion exerts a profound, but uncertain effect on the terrestrial carbon cycle. Therefore, the soil erosion intensity is uncertain in different terrains. Previous studies have focused on the slope and intensity of soil erosion, while ignored the special terrain such as gully created by erosion. To advance the understanding of the mineralization dynamics of soil organic carbon (SOC) from the micro perspective, the relationship between soil erosion and carbon source and sink is expected to be further improved. In this study, we explored the impact of water erosion on SOC mineralization in the areas of gully erosion in Qingyuan mountain, Jiangxi, China by combining the 137Cs technique and laboratory incubation experiment, calculated the first-order kinetic model parameters of the SOC mineralization of bulk soil and aggregates in the area of gully erosion, and estimated the correlation between the factors that may affect SOC mineralization. The results showed that (1) the mineralization rates of SOC in the bulk soil and aggregates showed fluctuations and reached a peak, and finally became stable. The soil erosion intensity was significantly positively correlated (p < 0.05) with the cumulative mineralization of SOC. (2) The cumulative mineralization in the depositional area (489.67 mg kg−1) was higher than that in the erosional area (402.69 mg kg−1). (3) Soil macroaggregates were the main contributors to SOC mineralization (63.56%–92.28%), and the soil macroaggregate organic carbon mineralization dynamics was more sensitive to soil erosion. Additionally, significant effects (p < 0.05) of soil mechanical composition, capillary pores, saturated water content, and contents of carbon and nitrogen on SOC mineralization were observed. Erosion increased the risk of SOC loss by mineralization of SOC, especially in macroaggregates. The deposition process caused the enrichment and burial of SOC, and the background level of SOC and the content of macroaggregates in the depositional area were higher than those in the erosional area. The results showed that soil erosion increased the risk of SOC loss by mineralization of SOC based on laboratory simulation. The present study aiming at examining the effect of gully erosion on the mineralization and sequestration of SOC provides important insights into balancing the global carbon budget.

Biochar addition stabilized soil carbon sequestration by reducing temperature sensitivity of mineralization and altering the microbial community in a greenhouse vegetable field

Biochar is widely used for soil carbon sequestration and fertility improvement. However, the effects of biochar interacted with nitrogen (N) on the mineralization of soil organic carbon (SOC) and microbial community have not been thoroughly understood, particularly no reports have been published on the long term effects of biochar in vegetable field. Here, we examined soil properties, SOC mineralization and microbial community affecting by biochar (0, 20 and 40 t ha−1; C0, C1 and C2, respectively), N (0 or 240 t ha−1; N0 or N1, respectively) and their interaction in a greenhouse vegetable field. Results indicated that biochar addition increased soil pH, SOC, recalcitrant C pool, especially for the 40 t ha−1 treatment. Biochar addition generally decreased soil C-cycling enzyme activity while increasing N and P-cycling enzyme and oxidase activities. Biochar combined with N addition reduced SOC mineralization rate and metabolic quotient (qCO2) by 10.2–22.0% and 6.85–30.4%, respectively, across 15–35 °C and the temperature sensitivity (Q10) by 0.96–4.70%, except for the N1C2 at 25–35 °C. Apparent changes in bacterial alpha diversity and community structures were observed among treatments. Besides, biochar mixed with N application significantly enhanced the relative abundance of Proteobacteria and decreased Acidobacteria, while did not result in significant differences in fungal diversity and community composition. Redundancy analysis indicated that the microbial community composition shifts induced by the interaction between N and biochar were attributed to the changes in soil chemical properties, such as pH and SOC. Overall, the combination of biochar and N fertilizer is recommended to improve SOC sequestration potential and regulate bacterial community diversity and composition in vegetable field for sustainable intensification.

Biochar-Based Compost Affects Bacterial Community Structure and Induces a Priming Effect on Soil Organic Carbon Mineralization

Urban forests are key to mitigating the Urban Heat Island Effect, which contributes to temperature increases in urban areas. However, the trees in these forests are usually under stress because urban soil is typically degraded. Biochar/compost amendments help with soil management by improving the physiochemical properties and bacterial communities of soil. Here, we compared the physiochemical properties and bacterial communities before and after (1) biochar-only and (2) biochar-based compost amendments. Our results suggested that biochar-only application did not improve soil properties after 1 year of treatment, whereas in the biochar-based compost treatment, the soil properties and bacterial communities changed after just four months. The increase in potassium and decrease in organic material, calcium, and available phosphorus in the soil of the former treatment indicated that the nutrient uptake of its trees had improved. Although there was no significant variation in the soil’s total nitrogen, the higher abundance of potential nitrogen-fixing bacteria in the biochar-based treatment suggested that the soil contained a supplement to nitrogen. Our results show that biochar-based compost amendment improves soil quality and associated bacterial communities in urban forest management.

Shrubification decreases soil organic carbon mineralization and its temperature sensitivity in alpine meadow soils

Shrubification is widespread in global grasslands. However, whether shrubification promotes the mineralization of soil organic carbon (SOC) remains uncertain. We compared sizes and compositions of soil non-cellulosic and amino sugar pools, soil stoichiometry, SOC decomposition and its temperature sensitivity between herbaceous and shrubby patches in alpine meadows on the Qinghai-Tibetan Plateau. The SOC content and soil stoichiometric C/P and N/P ratios in shrubby patches markedly increased with increasing plant size compared with herbaceous areas, indicating the increased P limitation to microorganisms relative to C and N with SOC accumulation under shrubs. The mass ratio of galactose plus mannose to arabinose plus xylose in the non-cellulosic carbohydrate pool of plant input was higher under shrubs than under grasses but was generally similar in soils between herbaceous and shrubby patches. This suggests the retarded microbial transformation of plant-derived carbohydrates under shrubs. Shrubs decreased accumulation of microbial necromass in SOC but increased the proportion of fungal origin in the microbial necromass. Lower total CO2 efflux per unit mass of SOC at either 15 °C or 25 °C from shrubby than from herbaceous patches over the 76-day incubation was mainly associated with the increased soil C/P or N/P ratio under shrubs. Shrubs decreased temperature sensitivity of SOC decomposition compared with grasses only at 20–40 cm soil depth, where microbial-synthesized substances had greater dominance over organic matter than at 0–20 cm depth and were less abundant under shrubs relative to grasses. Our findings show that increased P limitation to microorganisms in shrubification resulted in the decreased SOC decomposability and indicate that microbial-synthesized substances determined the temperature sensitivity of SOC mineralization. Therefore, shrubification mitigates CO2 emissions in grasslands by decreasing SOC mineralization and its temperature sensitivity in the context of global warming.

Effect of Two Exogenous Organic Acids on the Excitation Effect of Soil Organic Carbon in Beijing, China

Significance: The study of the effects and pathways of catechol and pyrogallic acid on soil organic carbon mineralization has a positive effect on mastering soil carbon transformation. Methods and objectives: In this study, we took 0–20 cm soil from Pinus tabulaeformis forest as an object to investigate the effects of catechol and pyrogallic acid with different concentrations on soil organic carbon mineralization through a 60-day mineralization incubation test. The soil active carbon content and changes in soil microbial diversity and community composition were analyzed by using single exponential fitting, quantitative PCR, and high-throughput sequencing to explore the influencing mechanisms of catechol and pyrogallic acid on soil organic carbon excitation. Results: Catechol and pyrogallic acid had the effect of enhancing the soil organic carbon mineralization and soil active carbon content, and the higher the concentration, the stronger the enhancement effect. Catechol reduced the Ace index, Chao1 index, and Shannon index of bacteria and fungi, and further changed the relative abundance of two dominant groups (Proteobacteria and Acidobacteriota) in bacteria and Basidiomycota in fungi at high concentrations. There was no obvious regularity in the effects of pyrogallic acid on bacteria and fungi, but the Ace index and Chao1 index of bacteria underwent drastic and disordered changes. Conclusions: Catechol and pyrogallic acid can trigger positive excitation of the soil organic carbon through two pathways: increasing the soil active carbon content and modulating soil microorganisms, but the way they modulate soil microorganisms are different. Catechol regulates soil microorganisms by reducing the number, richness, and evenness of the bacteria and fungi species, as well as the community composition, while the way pyrogallic acid regulates only closely relates to the changes in the number, richness, and evenness of bacteria species.

Impact of Pre-Ozonation during Nanofiltration of MBR Effluent.

This study aimed to investigate the impact of real MBR effluent pre-ozonation on nanofiltration performances. Nanofiltration experiments were separately run with non-ozonated real MBR effluent, ozonated real MBR effluent and synthetic ionic solution mimicking the ionic composition of the real MBR effluent. The specific UV absorbance and the chemical oxygen demand were monitored during ozonation of real effluent, and the mineralization rate was calculated through the quantitative analysis of dissolved organic carbon. The membrane structure was characterized using SEM on virgin and fouled membrane surfaces and after different cleaning steps. The results confirm the low effect of the ozonation process in terms of organic carbon mineralization. However, the chemical oxygen demand and the specific UV absorbance were decreased by 50% after ozonation, demonstrating the efficiency of ozonation in degrading a specific part of the organic matter fraction. A benefic effect of pre-ozonation was observed, as it limits both fouling and flux decrease. This study shows that the partial mineralization of dissolved and colloidal organic matter by ozonation could have a positive effect on inorganic scaling and decrease severe NF membrane fouling.

Carbon‑sulfur coupling in a seasonally hypoxic, high-sulfate reservoir in SW China: Evidence from stable C[sbnd]S isotopes and sulfate-reducing bacteria

Anthropogenic input of sulfate (SO42−) in reservoirs may enhance bacterial sulfate reduction (BSR) under seasonally hypoxic conditions in the water column. However, factors that control BSR and its coupling to organic carbon (OC) mineralization in seasonally hypoxic reservoirs remain unclear. The present study elucidates the coupling processes by analyzing the concentrations and isotopic composition of dissolved inorganic carbon (DIC) and sulfur (SO42−, sulfide) species, and the microbial community in water of the Aha reservoir, SW China, which has high SO42− concentration due to the inputs from acid mine drainage about twenty years ago. The water column at two sites in July and October revealed significant thermal stratification. In the hypoxic bottom water, the δ13C-DIC decreased while the δ34S-SO42− increased, implying organic carbon mineralization due to BSR. The magnitude of S isotope fractionation (Δ34S, obtained from δ34Ssulfate-δ34Ssulfide) during the process of BSR fell in the range of 3.4‰ to 27.0‰ in July and 21.6‰ to 31.8‰ in October, suggesting a change in the community of sulfate-reducing bacteria (SRB). The relatively low water column stability in October compared to that in July weakened the difference of water chemistry and ultimately affected the SRB diversity. The production of DIC (ΔDIC) scaled a strong positive relationship with the Δ34S in July (p < 0.01), indicating that high OC availability favored the survival of incomplete oxidizers of SRB. However, in October, Δ13C-DIC was correlated with the Δ34S in the bottom hypoxic water (p < 0.01), implying that newly degraded OC depleted in 13C could favor the dominance of complete oxidizers of SRB which caused greater S isotope fractionation. Moreover, the sulfide supplied by BSR might stimulate the reductive dissolution of Fe and Mn oxides (Fe(O)OH and MnO2). The present study helps to understand the coupling of C and S in seasonally hypoxic reservoirs characterized by high SO42− concentration.

Quantitative Characterization for Pore Connectivity, Pore Wettability, and Shale Oil Mobility of Terrestrial Shale With Different Lithofacies—A Case Study of the Jurassic Lianggaoshan Formation in the Southeast Sichuan Basin of the Upper Yangtze Region in Southern China

Some major hydrocarbon-bearing basins are rich in shale with terrestrial facies in China, which may provide abundant terrestrial shale oil and gas resources. This work studied the Jurassic Lianggaoshan Formation in the Southeast Sichuan Basin of the upper Yangtze Region. Core samples were chosen for the total organic carbon content and mineral composition analyses to classify shale lithofacies. Afterward, pore connectivity, pore wettability, and shale oil mobility with different lithofacies were characterized by spontaneous imbibition, nuclear resonance, and centrifugation. Conclusions are as follows: the pore connectivity of organic-rich clay shale was mostly between moderate to good with oil-prone wettability and high mobile oil saturation. The organic-rich mixed shale has moderate to good pore connectivity, water-prone wettability, and the highest mobile oil saturation. Organic matter–bearing clay shale has bad to moderate pore connectivity. Meanwhile, its pore wettability covers oil wetting, mixed wetting, oil-prone wetting, and water-prone wetting. Its mobile oil saturation was moderate. Regarding organic matter–bearing mixed shale, the pore connectivity was bad to moderate with mixed-wetting pore wettability and moderate mobile oil saturation.

The regulators of soil organic carbon mineralization upon lime and/or phosphate addition vary with depth

Knowledge of the key factors regulating soil organic carbon (OC) mineralization in response to fertilizers and lime application is essential to understanding the effects of agricultural land management on soil OC preservation. Microbial community composition and OC availability to microorganisms have been proposed as the two most imperative factors controlling soil OC mineralization, although their relative importance is still under debate. Here we performed a laboratory incubation in combination with high-throughput sequencing and structural equation modeling to examine the mechanisms underlying the responses of OC mineralization in the topsoil and the subsoil of a volcanic soil (an Andosol) to the additions of lime and/or phosphate. Results showed that lime and/or phosphate additions induced distinct shifts in the microbial community composition and functional profiles in the topsoil and the subsoil. We found that OC mineralization relied on microbial community composition and functionality in the topsoil but was strongly related to the quality and quantity of the water-extractable OC (indicative of the OC availability) in the subsoil. These data suggest that the key regulator controlling the response of OC mineralization to lime and/or P additions shifts from microbial community composition to OC availability as soil depth increases in the Andosol. Our findings highlight the central role of mechanisms controlling soil OC mineralization in regulating the responses of mineralization to intensive agricultural management practices.

Back to the Future: Restoring Northern Drained Forested Peatlands for Climate Change Mitigation

Draining peatlands for forestry in the northern hemisphere turns their soils from carbon sinks to substantial sources of greenhouse gases (GHGs). To reverse this trend, rewetting has been proposed as a climate change mitigation strategy. We performed a literature review to assess the empirical evidence supporting the hypothesis that rewetting drained forested peatlands can turn them back into carbon sinks. We also used causal loop diagrams (CLDs) to synthesize the current knowledge of how water table management affects GHG emissions in organic soils. We found an increasing number of studies from the last decade comparing GHG emissions from rewetted, previously forested peatlands, with forested or pristine peatlands. However, comparative field studies usually report relatively short time series following rewetting experiments (e.g., 3 years of measurements and around 10 years after rewetting). Empirical evidence shows that rewetting leads to lower GHG emissions from soils. However, reports of carbon sinks in rewetted systems are scarce in the reviewed literature. Moreover, CH4 emissions in rewetted peatlands are commonly reported to be higher than in pristine peatlands. Long-term water table changes associated with rewetting lead to a cascade of effects in different processes regulating GHG emissions. The water table level affects litterfall quantity and quality by altering the plant community; it also affects organic matter breakdown rates, carbon and nitrogen mineralization pathways and rates, as well as gas transport mechanisms. Finally, we conceptualized three phases of restoration following the rewetting of previously drained and forested peatlands, we described the time dependent responses of soil, vegetation and GHG emissions to rewetting, concluding that while short-term gains in the GHG balance can be minimal, the long-term potential of restoring drained peatlands through rewetting remains promising.