Soluble Organic Carbon Research Articles

Effect of exogenous thermophilic biocontrol agent inoculum on the high temperature chicken manure composting.

Aerobic composting is an effective method for utilizing chicken manure. However, its low carbon to nitrogen (C/N) ratio leads to slow heating and short high-temperature phases, which reduce composting efficiency and product quality. To address this issue, splinted mushroom cultivation residues were added to adjust the C/N ratio, and exogenous thermophilic composting strains were introduced to increase composting temperature. This study analyzed the relationship between physicochemical metabolites and microbial community structure during high-temperature chicken manure composting. Based on metagenomic and physicochemical analyses, results showed that the exogenous microbial agents extended the thermophilic phase by three-times, reduced the heating phase duration by 75%, and increased nitrogen, phosphorus, potassium, and soluble organic carbon contents by 3.61, 21.63, 7.21, and 39.03%, respectively. Genes associated with amino acid metabolism were significantly enriched during the heating phase, while genes involved in the tricarboxylic acid cycle were more active in the thermophilic phase. During the thermophilic phase, bacterial diversity and richness decreased compared to the heating and cooling phases. Functional microbes such as Bacillus, Caldicoprobacter, and Virgibacillus showed a positive correlation with the key differential metabolites. While Actinomadura, Saccharomonospora, Paenibacillus, and Aneurinibacillus displayed an opposite correlation. Further experiments demonstrated that the increased temperature during the thermophilic phase triggered the upregulation of oleic acid metabolism and piperidine metabolism pathways in functional microorganisms, leading to the production of heat stabilizers and protective agents like oleic acid, gallic acid, and 2-piperidone. This phenomenon helped maintain microbial viability during the thermophilic phase and improved composting efficiency.

Effects of Straw Addition on Soil Priming Effects Under Different Tillage and Straw Return Modes.

This study aims to investigate the impact of straw addition on soil activation effects under different tillage practices, providing a scientific basis for establishing reasonable straw return measures in the southern Northeast Plain, thus enhancing soil fertility, and mitigating greenhouse effects. Soil samples were collected from various straw return practices that were conducted continuously for two years as follows: rotary tillage without straw return (RTO), deep tillage combined with straw incorporation (PT), rotary tillage with straw incorporation (RT), and no-till with straw cover (NT). The samples were incubated in the dark at 25 °C for 70 days. We measured the CO2 release rate and cumulative release, apparent activation effect, soil organic carbon, active microbial biomass organic carbon, soluble organic carbon, and easily oxidizable organic carbon to clarify the effects of straw addition on soil activation under different tillage practices. The results indicate that a straw addition promotes the mineralization of soil organic carbon while also increasing the content of active organic carbon components. The CO2 release rates and cumulative release under different tillage practices were as follows: PT > NT > RT. The contents of the active microbial biomass organic carbon, soluble organic carbon, and easily oxidizable organic carbon increased by 16.62% to 131.88%, 4.36% to 57.59%, and 12.10% to 57.97%, respectively, compared to the control without the straw addition. Except for the RT practice, the addition of straw significantly enhanced the instability of soil organic carbon in the PT, NT, and RTO practices, with increases of 51.75%, 48.29%, and 27.90%, respectively. Different straw return practices altered the physical and chemical properties of the soil, resulting in significant differences in the strength of the apparent activation effect. Notably, the apparent activation effect of RT was reduced by 86.42% compared to RTO, while that of NT was reduced by 36.99% compared to PT. A highly significant positive correlation was observed between the apparent activation effect and the unstable carbon components in the soil, indicating that higher levels of easily decomposable organic carbon corresponded to stronger apparent activation effects. In conclusion, it is recommended that in this region, rotary tillage should be adopted for straw return in the first 2 to 3 years, as this practice is beneficial for the formation and stabilization of organic carbon in the short term. As the duration of straw return increases, adjustments can be made based on the degree of soil organic carbon retention and soil fertility status.

Effects of Litter Removal and Biochar Application on Soil Properties in Urban Forests of Southern China

Urban forests are crucial components of cities, serving as vital ‘green lungs’ that embody urban civilization and sustainability. Despite their significance in maintaining the urban environment and ecological functions, management practices for urban forests can be unreasonable at times. This study investigated the impact of two common practices, litter removal and biochar application, on soil properties in an urban forest in Changsha city, China. The aim was to understand how these practices affect soil carbon, nutrients, and microbial activity in urban settings. The results showed that soil water content (SWC), pH, available phosphorus (AP), and soil microbial biomass carbon (SMBC) were significantly reduced in areas where litter was removed compared to areas where litter was retained. Conversely, biochar application led to a significant increase in SWC, pH, AP, and SMBC. The treatment alone had no significant effects on total nitrogen (TN), soil organic carbon (SOC), and soluble soil organic carbon (SSOC) in the examined urban forests. However, the SOC and SSOC contents significantly increased over time with biochar application. Our results demonstrated that the influences of litter removal and biochar application on soil property were attributed to the regulation of AP and SMBC in the studied urban forests. This study provides a scientific basis and reference for understanding the sustainable management of urban environments and guiding future conservation efforts in urban greening spaces.

Variation in Bacterial and Fungal Communities in Soils from Three Major Apple Pear (Pyrus bretschneideri Rehd.) Orchards.

Microbial communities are closely related to the overall health and quality of soil, but studies on microbial ecology in apple pear orchard soils are limited. In the current study, 28 soil samples were collected from three apple pear orchards, and the composition and structure of fungal and bacterial communities were investigated by high-throughput sequencing. The molecular ecological network showed that the keystone taxa of bacterial communities were Actinobacteria, Proteobacteria, Gemmatimonadetes, Acidobacteria, Nitrospirae, and Chloroflexi, and the keystone taxon of fungal communities was Ascomycota. Mantel tests showed that soil texture and pH were important factors shaping soil bacterial and fungal communities, and soil water soluble organic carbon (WSOC) and nitrate nitrogen (NO3--N) were also closely related to soil bacterial communities. Canonical correspondence analysis (CCA) and variation partition analysis (VPA) revealed that geographic distance, soil texture, pH, and other soil properties could explain 10.55%, 13.5%, and 19.03% of the overall variation in bacterial communities, and 11.61%, 13.03%, and 20.26% of the overall variation in fungal communities, respectively. The keystone taxa of bacterial and fungal communities in apple pear orchard soils and their strong correlation with soil properties could provide useful clues toward sustainable management of orchards.

Effects of filter-feeding fish faeces on microbial driving mechanism of lake sediment carbon transformation

Silver carp (Hypophthalmichthys molitrix) can filter the carbon in the food taken up by phytoplankton and plays an important role in carbon fixation. In this study, the faeces of silver carp, the dominant fish species in Qiandao Lake, China, were collected and subjected to a closed incubation and transformation experiment for three months. The physical and chemical indices of water and sediment mixture, carbon metabolic enzyme activity, and microbial sequences were analyzed to identify the key microbial strains that affect carbon transformation as well as the main factors influencing carbon transformation. The results showed maximum CO2 and CH4 emission fluxes on day 15 of fish faeces and sediment interaction. In the faeces addition group, the contents of soluble organic carbon, soluble inorganic carbon, SO42−, and PO43− were significantly increased, while the dissolved oxygen content was significantly decreased. Furthermore, the pH, total carbon content, volatile suspended solids content, and activities of four carbon-metabolizing enzymes were significantly increased in the faeces addition group. The 16sRNA analysis of methanogenic and methane-oxidizing bacteria showed that Euryarchaea and Pseudomonas accounted for the highest proportion respectively. The most significant differences expression were found for Methylbacterium in the methanogenic bacteria and Methylobacter in the methane oxidizing bacteria. Structural variance model showed that interaction of fish faeces and sediments mainly caused changes in sulfate content, leading to variations in methanogens and methanotrophs and promotion of CH4 emission. The results of this study can provide a theoretical reference for the mechanism of carbon reduction and emission reduction of lake filter-feeding fish.

Assessing and Quantifying the Carbon, Nitrogen, and Enzyme Dynamics Effects of Inter-row Cover Cropping on Soils and Apple Tree Development in Orchards

Cover crops between rows in orchards can improve the development of soil resources and increase agricultural productivity. However, there have been few reports of cover crops that can act as a “green manure” in apple orchards across arid and semiarid zones. This study investigated the effects of planting interrow vegetation on soil properties and apple tree performance during a 32-month experiment. There were six treatments: clean cultivation as a control; natural grass planting; planting with ryegrass; planting with alfalfa; planting with tall fescue; and planting with villous wild pea cover crops. The treatments primarily affected the 0- to 20-cm surface soil layer. Soil carbon, nitrogen, and enzyme levels initially decreased (during the first 12–24 months); then, they increased (24–32 months). The cover crops significantly increased nutrient contents (soluble organic carbon, microbial carbon and nitrogen, alkaline dissolved nitrogen, nitrate nitrogen, and ammonium nitrogen) in the 0- to 20-cm soil layer by more than 19.6% and increased the related enzyme activities by more than 25.2%. The alfalfa and wild pea alleys had a stronger effect on the soil environment than the control, natural grass, ryegrass, and tall fescue alley treatments; however, after 32 months, the alfalfa treatment inhibited fruit tree growth and development. This was unexpected because alfalfa seemed to have a positive effect on soil fertility characteristics. Under local ecological conditions, villous wild pea had the greatest effect on apple orchard productivity and significantly increased short branching by 15.9%, fruit weight per fruit by 12.6%, yield per plant by 8.6%, and soluble sugar content by 10.5% compared with clean cultivation. The correlation analysis showed that there were significant or highly significant positive correlations between fruit tree performance and soil carbon, nitrogen, and enzyme activity levels as the soil layer depth increased. Therefore, under local ecological conditions, cover crops have a greater effect on orchard surface soil fertility than on deeper soils, and intercropping with villous wild pea potentially produces the greatest improvement in apple orchard productivity.

Conversion of farmland to forest or grassland improves soil carbon, nitrogen, and ecosystem multi-functionality in a subtropical karst region of southwest China

The conversion of farmland to forest in China has been recognized for its positive impact on above-ground vegetation and carbon sequestration. However, the impact on soil quality during land conversion, particularly in vulnerable karst areas, has received less attention. In this study conducted in a karst area of southwest China, eight different farmland conversion strategies were investigated to assess improvements in surface soil carbon, nitrogen, and ecosystem multi-functionality (EMF). Our results showed that farmland converted to afforestation areas or farmland that was abandoned contained higher amounts of carbon (total, organic, active) and ammonium nitrogen (NH4+-N) in the soil compared to farmland converted to grassland or maize crop. Soluble organic carbon levels were higher in afforestation and grassland areas compared to maize crop controls. By contrast, soil from grassland and abandoned land exhibited higher levels of nitrate nitrogen (NO3--N) compared to afforestation land or maize crop controls. There were no differences in NH4+-N content between any condition, except for afforestation land that specifically contained the Zenia insignis plant species. Afforestation land consistently exhibited higher EMF values than grassland. Pearson correlation analysis revealed positive relationships between soil indices and EMF scores, except for NO3--N.Random forest analysis explained 95% of the variation in soil EMF and identified specific soil factors: total carbon, organic carbon, active labile organic carbon, total nitrogen, and ammonium nitrogen, as the main drivers of soil multi-functionality. Our studies show how various reforestation strategies can enhance soil nutrient sequestration and improve soil multi-functionality of farmland in the karst areas.These findings provide insight into sustainable soil management practices for converting farmland into natural areas.

Determination of Soil Carbon Pools in Selected Soils of Abia State, Nigeria

Soil carbon pools exist in Abia State soils but variation, quantification and speciation remain unascertained. This study was carried out on soils collected from two locations (Umuahia North and Ikwuano LGAs) under three land use systems: arable land (AL), forest land (FL) and palm plantation (PP). The aim of the study was to assess carbon pools in the study soil. Laboratory data was subjected to analysis of variance (ANOVA) in Randomized Complete Block Design (RCBD). Significantly different means were separated using Fisher’s least significant difference (F-LSD) at 5% level of probability (p≤0.05). Correlation analysis was used to assess the relationship between the selected soil properties. It was observed that organic carbon increased significantly (p<0.05) 2.47 under forest land in Umuahia North and decreased to 0.97 under arable land in Ikwuano, permanganate oxidizable carbon (POC) increased significantly in Umuahia North (p<0.05) while decreasing in Ikwuano, the POC interaction on the both locations were significant, water soluble organic carbon (WSOC) and microbial biomass carbon (MBC) were neither significant in location, land use or their interaction.

Mollisol Erosion-Driven Efflux of Energetic Organic Carbon and Microflora Increases Greenhouse Gas Emissions from Cold-Region Rivers.

Massive soil erosion occurs in the world's Mollisol regions due to land use change and climate warming. The migration of Mollisol organic matter to river systems and subsequent changes in carbon biogeochemical flow and greenhouse gas fluxes are of global importance but little understood. By employing comparative mesocosm experiments simulating varying erosion intensity in Mollisol regions of northeastern China, this research highlights that erosion-driven export and biomineralization of terrestrial organic matter facilitates CO2 and CH4 emission from receiving rivers. Stronger Mollisol erosion, as represented by a higher soil-to-water ratio in suspensions, increased CO2 efflux, particularly for the paddy Mollisols. This is mechanistically attributable to increased bioavailability of soluble organic carbon in river water that is sourced back to destabilized organic matter, especially from the cultivated Mollisols. Concurrent changes in microbial community structure have enhanced both aerobic and anaerobic processes as reflected by the coemission of CO2 and CH4. Higher greenhouse gas effluxes from paddy Mollisol suspensions suggest that agricultural land use by supplying more nitrogen-containing, higher-free-energy organic components may have enhanced microbial respiration. These new findings highlight that Mollisol erosion is a hidden significant contributor to greenhouse gas emissions from river water, given that the world's four major Mollisol belts are all experiencing intensive cultivation.

Response of Potassium Humate Extracted from Different Organic Sources on Yield and Quality of Green Chilli

Aim: In recent trend of organic farming, use of humic substances plays important role, as it act as biostimulants to boost the yield of crop. Humic substances can be easily obtained by locally available organic sources. Hence, three different organic sources viz. Farm Yard Manure (FYM), vermicompost, lignite were characterized for their physico-chemical properties and quality parameters along with nutrients to judge their quality and maturity to extract humic substances. The potassium salt of humic acid extracted from these three sources were used as foliar application at different concentrations to study their effects on yield and quality of green chilli. Study Design: The pot culture experiment was conducted in Completely Randomized Design comprising eleven treatments with three replications. Place and Duration of the Study: The experiment was conducted in rabi season 2021-22 at College of Agriculture, Karad, Maharashtra, India. Methodology: Three organic sources viz. Farm Yard Manure (FYM), vermicompost and lignite were used to extract humic substances (humic and fulvic acid). These organic sources were studied for their physico-chemical properties and quality parameters along with their nutrient status to compare their quality and maturity for extraction of humic substances. Humic substances obtained from these different sources were studied for their content and characteristics. The potassium humate extracted from these organic sources were used in a pot culture study on green chilli, comprising eleven treatments and three replications. The different levels of potassium humate (200 to 600 ppm) were used as foliar application on transplanted chilli at 30 and 45 days after transplanting (DAT) along with recommended dose of fertilizers (GRDF) for studying its effects on yield and quality of green chilli. Results: Among all the three organic sources, vermicompost was reported as the best organic source to extract humic substances from its physico-chemical properties viz. pH (6.9), EC (0.3 dS m-1), water soluble organic carbon (0.76 %) and C:N ratio (18.0), which are considered as quality and maturity parameters to obtain good quality humic substances. Nutrient status for macro and micronutrients were reported to be higher in vermicompost followed by FYM and least content in lignite. In the pot culture experiment, the foliar application of potassium humate extracted from vermicompost resulted in significant improvement in fresh and dry yield of chilli fruit and stalk as compared to potassium humate application extracted from FYM and lignite. Among the various concentrations used (200-600 ppm) for the foliar application of potassium humate, application @ 400 ppm extracted from vermicompost along with GRDF (T7) was reported as the best treatment resulting in significantly increase in the fresh and dry yield of chilli fruits and stalk. Further, it was noticed that the same treatment was observed to be effective in significant improvement of the ascorbic acid content as quality parameter in fresh green chilli fruits.

Nutrient dynamics in wetland systems associated with hydrological and anthropogenic variations in the south of Samborombón Bay, Argentina

Wetlands provide numerous ecosystem services to the environment, such as nutrient removal and storage. The aim of this work is to evaluate the nutrient dynamics in different sectors within wetland systems in the south of the Samborombón Bay (Argentina) based on hydrological and/or anthropogenic variations. For this purpose, the hydrological features of the wetland were defined through the analysis of satellite images, precipitation and tidal data, and field surveys. Three sectors were identified in the wetland: one with tidal influence, another which is dependent on rainfall, and another that receives inputs from rainfall and from a sewage effluent treatment plant. In order to analyze the nutrient dynamics, samples of surface water, groundwater, and sediments were collected from these sectors. Measurements of pH and electrical conductivity were determined in situ in water samples, while the concentration of inorganic forms of phosphorus and nitrogen, soluble reactive silica, and organic carbon were determined through laboratory analysis. Also, bioavailable phosphorus, organic matter, pH, and electrical conductivity were determined in the sediment samples collected. Statistical analysis of the data reveals differences between the sectors and allows the interpretation of the dynamics of the studied components in the wetland. Electrical conductivity distinguishes the intertidal sectors of the wetland while components associated with P and N discriminate the sectors with inputs from the sewage effluent treatment plant. On the other hand, soluble reactive silica, organic carbon, and organic matter do not seem to be influenced by the tide or effluent discharge. This study demonstrates that the studied wetland works as a nutrient retention area, providing ecosystem services to local inhabitants. Although these services can be utilized, they require a continuous monitoring over time to provide an early warning in case the variations in P and N cycles could lead to eutrophication or wetland degradation.

Rice straw increases microbial nitrogen fixation, bacterial and nifH genes abundance with the change of land use types.

Soil microorganisms play an important role in soil ecosystems as the main decomposers of carbon and nitrogen. They have an indispensable impact on soil health, and any alterations in the levels of organic carbon and inorganic nitrogen can significantly affect soil chemical properties and microbial community composition. Previous studies have focused on the effects of carbon and nitrogen addition on a single type of soil, but the response of soil microorganisms to varying carbon and nitrogen inputs under different land soil use types have been relatively understudied, leaving a gap in our understanding of the key influencing factors. To address this gap, we conducted a study in the tropical regions of Hainan province, focusing on four distinct land use types: natural forest soil (NS), healthy banana soil (HS), diseased banana garden soil (DS), and paddy soil (PS). Within each of these environments, we implemented five treatments: CK, RS (rice straw), RSN (rice straw and NH4NO3), RR (rice root), and RRN (rice root and NH4NO3). Our aim was to investigate how soil bacteria response to changes in carbon and nitrogen inputs, and to assess their potential for biological nitrogen fixation. The results showed that the addition of rice straw increased the absorption and utilization of nitrate nitrogen by microorganisms. The addition of rice roots (RR) did not increase the absorption capacity of inorganic nitrogen by microorganisms, but increased the content of poorly soluble organic carbon. Most importantly, the addition of rice straw increased microbial respiration and the utilization efficiency of N2 by microorganisms, and the further addition of ammonium nitrate increased microbial respiration intensity. With the change of soil type, the rice straw increases microbial nitrogen fixation, bacterial and nifH genes abundance. Meanwhile, microbial respiration intensity is an important factor influencing the differences in the structure of bacterial communities. The addition of inorganic nitrogen resulted in ammonium nitrogen accumulation, reduced microbial richness and diversity, consequently diminishing the soil microorganisms to resist the environment. Therefore, we believe that with the change of soil types, corresponding soil nutrient retention strategies should be devised and incorporated while reducing the application of ammonium nitrogen, thus ensuring healthy soil development.

Deciphering the carbon and nitrogen component conversion in humification process mediated by distinct microbial mechanisms in composting from different domestic organic wastes.

This study aimed to compare the process of maturity and humus fraction evolution as well as bacterial community dynamics in composting from different domestic organic wastes (food waste (FW), and vegetable waste (VW)) and decipher the key biotic influencing factors of humic acid formation through correlation analysis and ecological network. The results showed that organic carbon components in FW with high ratio of soluble organic carbon and hemicellulose were more easily to be degraded in composting compared to VW. After 30days of composting, the content of HA-C generated by VW was 35.41%, higher than 29.01% of FW, and the growth rate of HA-C generated was 38.42% and 28.34%, respectively. PARAFAC analysis showed that the structure of HA generated in VW was more complex, and the proportion of humic acid-like components (C3 + C4) was 60.32%, while FW only accounted for 43.86%. However, the evolution growth rate of aromatic components in HA in FW was 26.88% in 30days of compost, which was higher than 15.17% in VW. High-throughput sequencing indicated that Lactobacillus was the initial dominated genera in composting from different domestic wastes. Thermobifida, Thermovum, and Pusillimas as well as Aeribacillus were core bacterial genera that promoted the humification process in FW and VW, respectively. Network analysis showed that there was higher bacterial interacted connection degree and complexity in FW compared to VW. This study was of great significance for optimizing organics conversion and humification efficiency of household waste composting.

Molecular-level insights into the temperature-dependent formation dynamics and mechanism of water-soluble dissolved organic carbon derived from biomass pyrolysis smoke

Water soluble organic carbon (WSOC) derived from biomass pyrolytic smoke is deposited through atmospheric aerosols, negatively affecting aquatic ecological quality and safety. However, the temperature-dependent molecular diversity and dynamic formation of smoke-derived WSOC remain poorly understood in water. Herein, we explored the molecular-level formation mechanism of pyrolytic smoke-derived WSOC in water to explain the evolution, heterogeneous correlations, and sequential responses of molecules and functional groups to increasing pyrolysis temperature. Two-dimensional correlation spectroscopy was used to innovatively establish the characteristic correlations between spectroscopy and Fourier transform-ion cyclotron resonance mass spectrometry. Temperature-dependent formation of WSOC exhibited diversity in absorbance/fluorescent components, unique/common molecules, and their chemical parameters, showing the simultaneous formation and degradation reactions. The common WSOC molecules with lower and higher degrees of oxidation showed significant positive and negative correlations with the fluorescent components, respectively. The primary sequential response of WSOC molecules to increasing pyrolysis temperature (lignin-like molecules → unsaturated hydrocarbons, condensed aromatic molecules → lipid-like/aliphatic-/peptide-like molecules) corresponded to the temperature response of functional groups (carboxylic/alcoholic → polysaccharides → aromatics/amides/phenolic/aliphatic groups), demonstrating well synergistic relationships between them. These novel findings will contribute to the comprehensive understanding and assessments of potential environmental behavior or risks of WSOC in aquatic ecosystems.

Effects of different artificial vegetation restoration modes on soil microbial community structuree in the soil erosion area of southern China

Investigating the effects of diverse artificial vegetation restoration methods on soil microbial communities is important for understanding soil health and achieving sustainable utilization of vegetation resources. In this study, the surface soil samples (0–10 cm) of three artificial vegetation restoration modes were selected as the research object which included the fenced forest, the arbor-shrub-grassland, and the chestnut forest in the soil and water loss area of South China. Three artificial vegetation restoration modes have significantly increased both the abundance and diversity of bacteria and fungi in areas affected by soil erosion, thus contributing to the stabilization of the ecosystem. Specifically, the arbor-shrub-grassland mode demonstrated the most significant improvements. Soil alkali nitrogen (71.10%, P = 0.000) and organic matter content (63.30%, P = 0.001) emerged as the primary factors driving this increase in bacterial and fungal diversity. After restoration, the composition of soil bacterial and fungal communities in soil erosion areas has undergone significant changes. However, it was observed that only the arbor-shrub-grassland mode could induce a shift in dominant bacterial species from Chloroflexi to Acidobacteria. Variations in soil bacterial and fungal community compositions across different modes were attributed to differences in soluble organic carbon (65.80%, P = 0.002) and soil bulk density (49.00%, P = 0.010). In conclusion, the increased fungal abundance and the bacterial shift observed in the arbor-shrub-grassland mode underscore its superior effectiveness in rehabilitating degraded soils, compared to both the fenced forest and the chestnut forest modes.

Spatial Distribution Patterns of Soil Organic Carbon in Karst Forests of the Lijiang River Basin and Its Driving Factors

The aim of this study was to explore the carbon storage potential of karst forest soils in the Lijiang River Basin, reveal the spatial pattern of soil organic carbon (SOC), investigate the contributions and pathways of each driving factor to the spatial distribution of soil organic carbon, and provide a scientific basis for assessing the carbon cycle function of karst forests in the region. We employed structural equation modeling (SEM) and correlation analysis to investigate the spatial distribution characteristics of forest soil organic carbon in different basin sections (upper, middle, and lower reaches) and soil layers at different depths of the Lijiang River. Additionally, the direct and indirect ratios of each factor were quantified. The results showed that the overall soil layer of karst forest soils in the Lijiang River Basin was shallow, and soil organic carbon was phenoconcentric. The distribution of soil organic carbon content in different watershed sections was upstream > downstream > midstream, and the distribution of readily oxidizable carbon (ROC) and dissolved organic carbon (DOC) was consistent, whereas the distribution of microbial biomass carbon (MBC) was upstream > midstream > downstream. The contribution of various biotic and abiotic factors to the spatial distribution of soil organic carbon in karst forests in the watershed was different, and their contributions were ranked in descending order as:soil physicochemical factors > soil organic carbon active fraction > sample elevation > sample species diversity, with the total effects of 1.148, 0.574, 0.284, and -0.013, respectively. Among them, the sample site elevation had only an indirect effect on soil organic carbon, and the soil organic carbon active fraction had only a direct effect on soil organic carbon. Among the driving factors, total soil nitrogen, soil oxidizable organic carbon, sample site species richness, and soil soluble organic carbon could be used as important predictors of soil organic carbon content in karst forests in the Lijiang River Basin. Therefore, it is necessary to establish an effective eco-environmental protection mechanism covering the whole Lijiang River Basin, to reduce and control the impact of anthropogenic disturbances (especially in the middle urban section of the Lijiang River Basin), and to enhance and protect the species diversity of karst forests in the basin in order to improve soil physicochemical properties, improve and enhance the content of the soil organic carbon active fraction, and enhance the soil organic carbon stocks of karst forests in the Lijiang River Basin through other effective ways, as well as to promote the enhancement of the regional forest carbon sink function.

Study on the effect of biomass charcoal-biogas application technology on soil carbon and nitrogen fractions and soil microbiological properties based on biomass charcoal-biogas application technology

Abstract The application of biogas and biomass charcoal to terrestrial crops and vegetables can promote their growth. The effects of the combined application of the two on soil carbon and nitrogen fractions and soil microbiological properties are not well-studied. Therefore, in this experiment, the red and yellow soil of Hangzhou City, Zhejiang Province, was used as the research object, and two factors, biomass charcoal and biogas, were set up to investigate the soil changes under the conditions of biomass charcoal-biogas application. One-way ANOVA and correlation analysis examined the differences in soil and crop radish under biomass charcoal-biogas application technology. The experimental results showed that the 2% application of hog manure charcoal at 350°C and 100% N amount of replacement of biosolids dosing treatments were the most effective, which could increase the content of organic matter, soluble organic carbon, etc., as well as the content of nitrogen in the soil, and improve the activity of soil enzymes. The enhancement of radish yield was greater with the application of swine manure charcoal with biogas than with the single application of both, and the maximum radish yield was achieved with the 100% N amount substitution of biogas with the application of swine manure charcoal at 2%-350°C treatment. The heavy metal contents in radish were below the limit values after 9 months of application of both biogas and biomass charcoal, which did not affect the edible safety of radish.

Cyanobacteria-based soil amendments in the soil-plant system: Effects of inoculations on soil nutrient and microbial dynamics under spring wheat growth

Cyanobacteria are promising alternatives to chemical fertilizers for managing nutrients and preserving soil function. In this study, two pot experiments were conducted to evaluate the effects of inoculations with the cyanobacterium Anabaena cylindrica on an arable Mollisol from the U.S. Upper Midwest and growth of spring wheat. Experiment 1 evaluated surface soil nutrient and microbial dynamics at early stages of wheat development. Experiment 2 evaluated the potential of microalgal inoculations (A. cylindrica and/or Chlamydomonas sp.) to replace urea and measured plant growth and soil parameters at three depths at harvest. Experiment 1 revealed inoculation increased surface soil soluble organic carbon (SolC), microbial biomass carbon (C), total nitrogen (N), mineral N, available phosphorus (P), and microbial activity. At day 42 after sowing, wheat plant N was higher in inoculated than non-inoculated soil, and the nitrate/nitrite level in inoculated soil significantly decreased in the presence of plants. In Experiment 2, inoculation had greater effects on surface soil than deeper soil depths for SolC, microbial biomass C and N, mineral N, and available-P. Grain yield was not statistically different in treatments with 100 % N from urea, 75 % N from A. cylindrica plus 25 % N-urea, and 100 % N from an algal mixture. Equivalent grain protein was achieved only when 25 % N from urea was replaced with N from A. cylindrica, highlighting the need for optimizing inoculation timing and plant N uptake. These results support the beneficial role of cyanobacteria-based inoculations for soil quality and plant growth, and as renewable resources for agricultural systems.

Nutrient loading weakens seagrass blue carbon potential by stimulating seagrass detritus carbon emission

Coastal nutrient loading has been linked to a decline in the capacity of seagrass ecosystems to sequester carbon (‘blue carbon’); however, the mechanisms are unclear. Here we investigated how nutrient loading can affect the contribution that seagrass plant material makes to blue carbon stocks by investigating plant quality-decomposition dynamics. Specifically, we used a combination of laboratory and field experiments to account for various changes in biogeochemical cycling from seagrass meadows, ranging from changes in leaf quality to CO2 fluxes. It was found that nutrient loading increased the ‘labile’ content of seagrass (i.e. increased levels of leaf nitrogen, phosphorus and soluble organic carbon (amino acid and soluble sugar content), and at the same time decreased levels of ‘recalcitrant’ carbon (i.e. materials that are harder for microbes to break down, such hemicellulose, cellulose and lignin contents). Nutrient-enriched leaves decomposed ∼ 18 % faster than non-enriched leaves (i.e. greater biomass loss from nutrient-affected seagrass), resulting in ∼ 80 % more CO2 emissions from nutrient-enriched seagrass. We also found that seagrass that naturally contained high levels of labile carbon at the start of the experiment were affected to a greater degree (i.e. higher CO2 emissions) by nutrients addition than seagrass that had high proportions of recalcitrant carbon to begin with. Overall, these findings suggest that nutrient loading can weaken the capacity of seagrass ecosystems to act as blue carbon sinks through its effect on seagrass leaf decomposability.

Metrological traceable calibration of organic carbon and elemental carbon based on laboratory-generated reference materials

Carbonaceous aerosol, including organic carbon (OC) and elemental carbon (EC), has significant influence on human health, air quality and climate change. Accurate measurement of carbonaceous aerosol is essential to reduce the uncertainty of radiative forcing estimation and source apportionment. The accurate separation of OC and EC is controversial due to the charring of OC. Therefore, the development of reference materials (RM) for the validation of OC/EC separation is an important basis for further study. Previous RMs were mainly based on ambient air sampling, which could not provide traceability of OC and EC concentration. To develop traceable RMs with known OC/EC contents, our study applied an improved aerosol generation and mixing technique, providing uniform deposition of particles on quartz filters. To generate OC aerosol with similar pyrolytic property of ambient aerosol, both water soluble organic carbon (WSOC) and water insoluble organic carbon (WIOC) were used, and amorphous carbon was selected for EC surrogate. The RMs were analyzed using different protocols. The homogeneity within the filter was validated, reaching below 2%. The long-term stability of RMs has been validated with RSD ranged from 1.7%–3.2%. Good correlation was observed between nominal concentration of RMs with measured concentration by two protocols, while the difference of EC concentration was within 20%. The results indicated that the newly developed RMs were acceptable for the calibration of OC and EC, which could improve the accuracy of carbonaceous aerosol measurement. Moreover, the laboratory-generated EC-RMs could be suitable for the calibration of equivalent BC concentration by Aethalometers.