Effects of biochar on soil microbial community and functional genes of a landfill cover three years after ecological restoration

Remediation strategy of biochar with different addition approaches on antibiotic resistance genes in riparian zones under dry wet alternation

The global prevalence of antibiotic resistance genes (ARGs) has aroused increasing concern due to its threat to ecological security and human health. Although biochar has been widely used for pollution remediation including ARGs, little is known its regulation on antibiotics and ARGs propagation under riparian zones, where undergo frequent occurrence of dry and wet alternations (DWA) caused by water-level fluctuation. Therefore, this study investigated the regulative effects of biochar through different addition approaches on ARGs spread in riparian zone sediments. Under DWA, the presence of biochar (2 % w/w) inhibited microbial diversity and function expression, especially for tiled biochar. In addition, compared with DWA, the tiled biochar decreased ARGs abundance by 45.36 %, while the well-mixed increased that by 269.02 %. The ARGs abundance in sediments was positively correlated with mobile genetic element abundance (R2=0.996, p < 0.05), indicative of high horizontal gene transfer potential of ARGs. Metabolomics revealed that both DWA and biochar significantly altered microbial metabolism pathways in sediments, involving sulfur metabolism and histidine metabolism. Furthermore, ARGs propagation in riparian zones may be dominantly driven by MGEs, especially by transposases and integrase. These findings highlight the tiled biochar remediation effects on ARGs in riparian zones under DWA caused by global warming.

Enhancing the Resilience of Agroecosystems Through Improved Rhizosphere Processes: A Strategic Review

As farming practices evolve and climate conditions shift, achieving sustainable food production for a growing global population requires innovative strategies to optimize environmentally friendly practices and minimize ecological impacts. Agroecosystems, which integrate agricultural practices with the surrounding environment, play a vital role in maintaining ecological balance and ensuring food security. Rhizosphere management has emerged as a pivotal approach to enhancing crop yields, reducing reliance on synthetic fertilizers, and supporting sustainable agriculture. The rhizosphere, a dynamic zone surrounding plant roots, hosts intense microbial activity fueled by root exudates. These exudates, along with practices such as green manure application and intercropping, significantly influence the soil's microbial community structure. Beneficial plant-associated microbes, including Trichoderma spp., Penicillium spp., Aspergillus spp., and Bacillus spp., play a crucial role in improving nutrient cycling and promoting plant health, yet their interactions within the rhizosphere remain inadequately understood. This review explores how integrating beneficial microbes, green manures, and intercropping enhances rhizosphere processes to rebuild microbial communities, sequester carbon, and reduce greenhouse gas emissions. These practices not only contribute to maintaining soil health but also foster positive plant-microbe-rhizosphere interactions that benefit entire ecosystems. By implementing such strategies alongside sound policy measures, sustainable cropping systems can be developed to address predicted climate challenges. Strengthening agroecosystem resilience through improved rhizosphere processes is essential for ensuring food security and environmental sustainability in the future. In conclusion, using these rhizosphere-driven processes, we could develop more sustainable and resilient agricultural systems that ensure food security and environmental preservation amidst changing climate situations.

In situ bioaccumulation of metals by Prosopis juliflora and its detoxification potential at the metal contaminated sites

Heavy metals emanate from diverse anthropogenic activities and the top soil in the vicinity of these activities acts as an immediate sink and facilitates diffusion of heavy metals into the food chain. In the semi-arid plains of India, Prosopis juliflora is the most common and dominant weed along the motorways and barren lands including industrial environs. This investigation hypothesizes the adaptive nature of Prosopis juliflora in the metal enriched soils and attempts to understand its hyper-accumulating potential of metals besides bioconversion/detoxification capability. Prosopis juliflora samples (root, stem, leaves, and pods) from 100 sites in the environs of anthropogenic activities (vehicular emissions and industrial operations) were analyzed for heavy metal concentrations (Cu, Fe, Cr, Cd, Ni, Pb). Prosopis juliflora accumulate metals at the rate of 0.138 mg/kg/day DW for Copper (Cu), Fe: 0.142 mg/kg/day DW, Cr: 0.114 mg/kg/day DW, Ni: 0.048 mg/kg/day DW, Pb: 0.052 mg/kg/day DW, Cd: 0.009 mg/kg/day DW. Furthermore, X-ray Photoelectron Spectroscopy (XPS) metal oxidation state analysis revealed that in the pods of Prosopis juliflora heavy metals (Fe, Cr, Pb) largely existed in non-toxic form (toxic:non-toxic - 3:6), while in the under canopy soil, metals predominantly existed in toxic form (toxic:non-toxic - 7:2); conclusively XPS results ascertains the heavy metal bioconversion/detoxification potential of the plant. These findings suggest that presence of Prosopis juliflora coppice in the barren landscapes across the transportation corridors and metal based industrial zones may ideally favor phyto-remediation of heavy metals.

Biochar's role in improving pakchoi quality and microbial community structure in rhizosphere soil

Background

Biochar amendments enhance crop productivity and improve agricultural quality. To date, studies on the correlation between different amounts of biochar in pakchoi (Brassica campestris L.) quality and rhizosphere soil microorganisms are limited, especially in weakly alkaline soils. The experiment was set up to explore the effect of different concentrations of biochar on vegetable quality and the correlation between the index of quality and soil bacterial community structure changes.

Methods

The soil was treated in the following ways via pot culture: the blank control (CK) without biochar added and with biochar at different concentrations of 1% (T1), 3% (T2), 5% (T3), and 7% (T4). Here, we investigatedthe synergistic effect of biochar on the growth and quality of pakchoi, soil enzymatic activities, and soil nutrients. Microbial communities from pakchoi rhizosphere soil were analyzed by Illumina MiSeq.

Results

The results revealed that adding 3% biochar significantly increased plant height, root length, and dry weight of pakchoi and increased the contents of soluble sugars, soluble proteins, Vitamin C (VC), cellulose, and reduced nitrate content in pakchoi leaves. Meanwhile, soil enzyme activities and available nutrient content in rhizosphere soil increased. This study demonstrated that the the microbial community structure of bacteria in pakchoi rhizosphere soil was changed by applying more than 3% biochar. Among the relatively abundant dominant phyla, Gemmatimonadetes, Anaerolineae, Deltaproteobacteria and Verrucomicrobiae were reduced, and Alphaproteobacteria, Gammaproteobacteria, Bacteroidia, and Acidimicrobiia relative abundance increased. Furthermore, adding 3% biochar reduced the relative abundance of Gemmatimonas and increased the relative abundances of Ilumatobacter, Luteolibacter, Lysobacter, Arthrobacter, and Mesorhizobium. The nitrate content was positively correlated with the abundance of Gemmatimonadetes, and the nitrate content was significantly negatively correlated with the relative abundance of Ilumatobacter. Carbohydrate transport and metabolism in the rhizosphere soil of pakchoi decreased, and lipid transport and metabolism increased after biochar application.

Conclusion

Overall, our results indicated that applying biochar improved soil physicochemical states and plant nutrient absorption, and affected the abundance of dominant bacterial groups (e.g., Gemmatimonadetes and Ilumatobacter), these were the main factors to increase pakchoi growth and promote quality of pakchoi. Therefore, considering the growth, quality of pakchoi, and soil environment, the effect of using 3% biochar is better.

Biochar modulating soil biological health: A review

Biochar can be used for multifunctional applications including the improvement of soil health and carbon storage, remediation of contaminated soil and water resources, mitigation of greenhouse gas emissions and odorous compounds, and feed supplementation to improve animal health. A healthy soil preserves microbial biodiversity that is effective in supressing plant pathogens and pests, recycling nutrients for plant growth, promoting positive symbiotic associations with plant roots, improving soil structure to supply water and nutrients, and ultimately enhancing soil productivity and plant growth. As a soil amendment, biochar assures soil biological health through different processes. First, biochar supports habitats for microorganisms due to its porous nature and by promoting the formation of stable soil micro-aggregates. Biochar also serves as a carbon and nutrient source. Biochar alters soil physical and chemical properties, creating optimum soil conditions for microbial diversity. Biochar can also immobilize soil pollutants and reduce their bioavailability that would otherwise inhibit microbial growth. However, depending on the pyrolysis settings and feedstock resources, biochar can be comprised of contaminants including polycyclic aromatic hydrocarbons and potentially toxic elements that can inhibit microbial activity, thereby impacting soil health.

Assessment of metal pollution and effects of physicochemical factors on soil microbial communities around a landfill

The physicochemical properties, chemical fractions of six metals (Cu, Zn, Pb, Cd, Cr, and Mn), and microbial communities of soil around a typical sanitary landfill were analyzed. The results indicate that soils around the landfill were from neutral to weak alkalinity. The contents of organic matter (OM), total nitrogen (TN), total phosphorous (TP), and activities of catalase, cellulase, and urease were significantly higher in landfill soils than those in background soils. Negative correlations were found between pH and metals. Cr was the dominant metal. Cu, Pb, Cr, and Mn were accumulated in the nearby farmland soils. Cd had the highest percentage of exchangeable fraction (33.7%-51.8%) in landfill and farmland soils, suggesting a high bioavailability to the soil environment affected by the landfill. Pb, Cr, and Mn existed mostly in oxidable fraction, and Cu and Zn were dominant in residual fraction. There was a low risk of soil metals around the landfill based on the RI values, while according to RAC classification, Cd had high to very high environmental risk. The MisSeq sequencing results showed that Actinobacteria, Proteobacteria, Chloroflexi, and Acidobacteria were the dominant phyla of bacteria, and the most abundant phylum of fungi was Ascomycota. The NMDS analysis revealed that the landfill could influence soil fungal communities more intensely than bacterial communities. TN, cellulase, and bioavailable metals (Pb-Bio and Cr-Bio) were identified to have main influences on microbial communities. Pb-Bio was the most dominant driving factor for bacterial community structures. For fungi, Pb-Bio was significantly negatively related to Olpidiomycota and Cr-Bio had a significantly negative correlation with Ascomycota. It manifests that bioavailable metals play important roles in assessing environmental risks and microbial community structures of soil around landfill.

Biochar Production and Characteristics, Its Impacts on Soil Health, Crop Production, and Yield Enhancement: A Review

Rapid urban expansion and a booming population are placing immense pressure on our agricultural systems, leading to detrimental impacts on soil fertility and overall health. Due to the extensive use of agrochemicals in agriculture, the necessity to meet the expanding demand for food has also resulted in unsustainable farming practices. Around the world, biochar, a multipurpose carbonaceous material, is being used to concurrently solve issues with enhancing soil fertility, plant growth, and development under both normal and stressful circumstances. It improves water retention, fosters nutrient absorption, and promotes microbial activity, creating a fertile environment that supports sustainable and resilient agriculture. Additionally, biochar acts as a carbon sink, contributing to long-term carbon sequestration and mitigating climate change impacts. The major benefit of biochar is that it helps the adsorption process with its highly porous structures and different functional groups. Understanding the elements involved in biochar formation that determine its characteristics and adsorptive capacity is necessary to assure the viability of biochar in terms of plant productivity and soil health, particularly biological activity in soil. This paper focuses on the development, composition, and effects of biochar on soil fertility and health, and crop productivity.

Effects of biochar on earthworms during remediation of potentially toxic elements contaminated soils

With the widespread use of biochar for soil remediation and improvement, its effects on soil organisms are receiving increased attention. The impacts of biochar on earthworms are still poorly understood. This study aimed to assess the potential ecotoxicity of rice husk biochar (RB) and sludge biochar (SB) on earthworms during potentially toxic elements (PTEs) contaminated soil remediation. The results showed that high rates of RB addition (5% and 10%) caused earthworm mortality, but SB addition did not affect earthworm survival. When added at non-lethal rates (3%), RB and SB addition did not affect survival, weight loss, and PTEs accumulation of earthworms, while resulting in apparent avoidance behavior and oxidative stress response. Among them, RB addition was more likely to cause avoidance behavior, while SB addition had a more pronounced stress effect on earthworms. Additionally, the bacterial communities in the earthworm gut were more sensitive to biochar addition than those in soil. SB addition had a greater impact on earthworm gut bacterial communities than RB addition. The addition of RB and SB increased the abundance of Bacillaceae while decreasing the abundance of Rhizobiaceae in the earthworm gut. This change in the composition of bacterial community may impact the nitrogen cycle and organic matter degradation functions of earthworms. The study suggests that RB and SB may have different effects on earthworms during PTEs-contaminated soil remediation, depending on their properties. It will assist us to understand the potential ecotoxicity of biochar and provide several guidance for its safe application.

Insight into the soil aggregate-mediated restoration mechanism of degraded black soil via biochar addition: Emphasizing the driving role of core microbial communities and nutrient cycling

Soil microbial communities are responsive to biochar application. However, few studies have investigated the synergistic effects of biochar application in the restoration of degraded black soil, especially soil aggregate-mediated microbial community changes that improve soil quality. From the perspective of soil aggregates, this study explored the potential microbial driving mechanism of biochar (derived from soybean straw) addition in black soil restoration in Northeast China. The results showed that biochar significantly improved the soil organic carbon, cation exchange capacity and water content, which play crucial roles in aggregate stability. The addition of biochar also significantly increased the concentration of the bacterial community in mega-aggregates (ME; 0.25-2 mm) compared with micro-aggregates (MI; <0.25 mm). Microbial co-occurrence networks analysis showed that biochar enhanced microbial interactions in terms of the number of links and modularity, particularly in ME. 16 S rRNA sequencing predicted that the expression of genes related to carbon (rbcL, acsA, gltS, aclB, and mcrA) and nitrogen (nifH and amoA) transformation increased after the addition of biochar. Furthermore, the functional microbes involved in carbon fixation (Firmicutes and Bacteroidetes) and nitrification (Proteobacteria) were significantly enriched and are the key regulators of carbon and nitrogen kinetics. Structural equation model (SEM) analysis further showed that the application of biochar promoted soil aggregates to positively regulate the abundance of soil nutrient conversion-related microorganisms, thereby increasing soil nutrient content and enzyme activities. These results provide new insights into the mechanisms of soil restoration through biochar addition.

Unraveling the effect of added microbial inoculants on ammonia emissions during co-composting of kitchen waste and sawdust: Core microorganisms and functional genes

Despite the role of microorganisms in nitrogen biotransformation has been extensively explored, how microorganisms mitigate NH₃ emissions in the transformation of nitrogen throughout the composting system is rarely addressed. The present study explored the effect of microbial inoculants (MIs) and the contribution of different composted phases (solid, leachate, and gas) on NH₃ emissions by constructing a co-composting system of kitchen waste and sawdust with and without the addition of MI. The results showed that NH₃ emissions increased markedly after adding MIs, in which the contribution of leachate ammonia volatilization to NH₃ emissions was most prominent. The core microorganisms of NH₃ emission had a clear proliferation owing to the MIs reshaping community stochastic process. Also, MIs can strengthen the co-occurrence between microorganisms and functional genes of nitrogen to promote nitrogen metabolism. In particular, the abundances of nrfA, nrfH, and nirB genes, which could augment the dissimilatory nitrate reduction process, were increased, thus enhancing NH₃ emissions. This study bolsters the fundamental, community-level understanding of nitrogen reduction treatments for agricultural.

Coupled effects of elevated CO2 and biochar on microbial communities of vegetated soil

Soil microbial communities are important for plant growth and establishing healthy ecosystems. Although biochar is widely adopted as a sustainable fertilizer, its influence on soil ecological functions is still unclear, especially under climate change such as elevated carbon dioxide concentration (eCO₂). This study explores the coupled effects between eCO₂ and biochar on microbial communities in soil planted with tree seedlings of Schefflera heptaphylla. Root characteristics and soil microbial communities were examined and interpreted with statistical analysis. Results show that biochar application at ambient carbon dioxide concentration (aCO₂) always improves plant growth, which is further promoted under eCO₂. Similarly, β-glucosidase, urease and phosphatase activities are enhanced by biochar at aCO₂ (p < 0.05). In contrast, only urease activity increases with biochar added at eCO₂ (p < 0.05). The beneficial effects of biochar on soil enzyme activities become less significant at eCO₂. Depending on biochar type, biochar can increase bacterial diversity and fungal richness at aCO₂. However, at eCO₂, biochar does not significantly affect microbial richness (p > 0.05) while microbial diversity is reduced by peanut shell biochar (p < 0.05). Owing to better plant growth under biochar application and eCO₂, plants are likely to become more dominant in specializing the microbial communities that are favourable to them. In such community, the abundance of Proteobacteria is the greatest and increases after biochar addition at eCO₂. The most abundant fungus also shifts from Rozellomycota to Ascomycota and Basidiomycota. These microbes can improve soil fertility. Even though the microbial diversity is reduced, using biochar at eCO₂ can further promote plant growth, which in turn enhances carbon sequestration. Thus, biochar application can be an effective strategy to facilitate ecological restoration under climate change and relieve the problem of eCO_2.

Response characteristics of antibiotic resistance genes and bacterial communities during agricultural waste composting: Focusing on biogas residue combined with biochar amendments

This research investigated biogas residue and biochar addition on antibiotic resistance genes (ARGs), mobile genetic elements (MGEs), and changes in bacterial community during agricultural waste composting. Sequencing technique investigated bacterial community structure and ARGs, MGEs changes. Correlations among physicochemical factors, ARGs, MGEs, and bacterial community structure were determined using redundancy analysis. Results confirmed that biochar and biogas residue amendments effectively lowered the contents of ARGs and MGEs. The main ARGs detected was sul1. Proteobacteria and Firmicutes were the main host bacteria strongly associated with the dissemination of ARGs. The dynamic characteristics of the bacterial community were strongly correlated with pile temperature and pH (P < 0.05). Redundancy and network analysis revealed that nitrate, intI1, and Firmicutes mainly affected the in ARGs changes. Therefore, regulating these key variables would effectively suppress the ARGs spread and risk of compost use.

Characteristics of carbon, nitrogen, phosphorus and sulfur cycling genes, microbial community metabolism and key influencing factors during composting process supplemented with biochar and biogas residue

Carbon (C), nitrogen (N), phosphorus (P), and sulfur (S) cycling functional genes and bacterial and fungal communities during composting with biochar and biogas residue amendments were studied. Correlations between microbial community structure, functional genes and physicochemical properties were investigated by network analysis and redundancy analysis. It was shown that the gene of acsA abundance accounted for about 50% of the C-related genes. Biogas residue significantly decreased the abundance of denitrification gene nirK. Biogas residues can better promote the diversity of bacteria and fungi during composting. Biochar significantly increased the abundance of Humicola. Redundancy analysis indicated that pile temperature, pH, EC were the main physicochemical factors affecting the microbial community. WSC and NO₃^--N have significant correlation with C, N, P, S functional genes. The research provides a theoretical basis for clarifying the metabolic characteristics of microbial communities during composting and for the application of biochar and biogas residues in composting.

The potential for biochar application in "Shatangju" (Citrus reticulate cv.) orchard on acid red soil: Biochar prepared from its organic waste in an orchard

Carbonization of agricultural and forestry wastes is the main use of biochar application in agriculture. In this study, the effects of biochar on the physical and chemical properties of soil and diversity in rhizosphere microorganisms, leaf nutrients and fruit quality of acid red soil in "Shatangju" (Citrus reticulate cv.) orchard were studied using organic wastes and small-scale carbonization furnaces from orchards were used to produce biochar. The results showed that the finished rate of biochar produced from the organic wastes in the orchard was approximately 37%, and the carbon content of the finished product was as high as 80%. The results suggested that the biochar produced in the orchard could meet the annual consumption of the orchard. Applying biochar can improve the physical and chemical properties of acid soil in the "Shatangju" orchard by enhancing the availability of various mineral nutrients such as nitrogen, phosphorus, potassium, calcium, magnesium and boron. The species and quantity of root and rhizosphere microbial communities (fungi, bacteria and archaea) increased, and the dominant bacterial group changed, manifested in the increase in microbial diversity. Biochar directly affected the soil pH value and increased the soil organic carbon content, which may be the main reason for the change in microbial diversity in the soil and rhizosphere of "Shatangju" in the orchard and pot tests. The fruit quality of each treatment group with biochar was also better than that of the control group and improved fruit coloring. In the pure soil test, whether or not chemical fertilizer was applied, 3% biochar amendments can provide a suitable pH value for "Shatangju" growth and are relatively stable. Regardless of whether or not fertilizer was applied, 1.5%-3% biochar improved the soil in the pot test. In the field, the biochar at a rate of 2.4 kg/plant to 3.6 kg/plant, respectively, was the best in improving soil physical and chemical properties, foliar nutrition and fruit quality. Therefore, the amount of biochar added in the open environment (if the garden) can be slightly adjusted according to the results of the closed environment test (pure soil test and pot test). In this experiment, we explored the self-recycling of organic carbon, mainly through the preparation of a simple small-scale biochar furnace suitable for the use by orchards, and selected the appropriate amount of biochar to improve the physical and chemical conditions of "Shatangju" orchard soil and increase fruit quality.

Long-term excessive application of K2SO4 fertilizer alters bacterial community and functional pathway of tobacco-planting soil

To improve tobacco leaf quality, excessive K2SO4 fertilizers were applied to soils in major tobacco-planting areas in China. However, the effects of K2SO4 application on soil microbial community and functions are still unclear. An eight-year field experiment with three kinds of K2SO4 amounts (low amount, K2O 82.57 kg hm-2, LK; moderate amount, K2O 165.07 kg hm-2, MK; high amount, K2O 247.58 kg hm-2, HK) was established to assess the effects of K2SO4 application on the chemical and bacterial characteristics of tobacco-planting soil using 16S rRNA gene and metagenomic sequencing approaches. Results showed that HK led to lower pH and higher nitrogen (N), potassium (K), sulfur(S) and organic matter contents of the soil than LK. The bacterial community composition of HK was significantly different from those of MK and LK, while these of MK and LK were similar. Compared to LK, HK increased the relative abundance of predicted copiotrophic groups (e.g. Burkholderiaceae, Rhodospirillaceae families and Ellin6067 genus) and potentially beneficial bacteria (e.g. Gemmatimonadetes phylum and Bacillus genus) associated with pathogens and heavy metal resistance, N fixation, dissolution of phosphorus and K. While some oligotrophic taxa (e.g. Acidobacteria phylum) related to carbon, N metabolism exhibited adverse responses to HK. Metagenomic analysis suggested that the improvement of pathways related to carbohydrate metabolism and genetic information processing by HK might be the self-protection mechanism of microorganisms against environmental stress. Besides, the redundancy analysis and variation partitioning analysis showed that soil pH, available K and S were the primary soil factors in shifting the bacterial community and KEGG pathways. This study provides a clear understanding of the responses of soil microbial communities and potential functions to excessive application of K2SO4 in tobacco-planting soil.

Effects of whole-orchard recycling on nitrate leaching potential in almond production systems

Inefficient nitrogen (N) fertilization and irrigation have led to unhealthy nitrate levels in groundwater bodies of agricultural areas in California. Simultaneously, high commodity prices and drought have encouraged perennial crop growers to turnover less-productive orchards, providing opportunities to recycle tree biomass in situ and to use high-carbon (C) residues to conserve soil and water resources. Although climate change adaptation and mitigation benefits of high-C soil amendments have been shown, uncertainties remain regarding the benefits and trade-offs of this practice for N cycling and retention. We used established almond [Prunus dulcis (Mill.) D. A. Webb] orchard trials on Hanford fine sandy loam with short-term and long-term biomass recycling legacies to better understand the changes in N dynamics and retention capacity associated with this practice. In a soil column experiment, labeled N fertilizer was added and traced into various N pools, including microbial biomass and inorganic fractions in soil and leachate. Shifts in microbial communities were characterized using the abundance of key N cycling functional genes regulating nitrification and denitrification processes. Our findings showed that, in the short term, biomass recycling led to N immobilization within the orchard biomass incorporation depth zone (0-15 cm) without impacts on N leaching potential. However, this practice drastically reduced nitrate leaching potential by 52%, 10 yr after biomass incorporation without an increase in N immobilization. Although the timing of these potential benefits as a function of microbial population and C and N biogeochemical cycles still needs to be clarified, our results highlight the potential of this practice to meaningfully mitigate nitrate discharges into groundwater while conserving soil resources.

Biochar Addition Altered Bacterial Community and Improved Photosynthetic Rate of Seagrass: A Mesocosm Study of Seagrass Thalassia hemprichii

Seagrass meadows, as typical “blue carbon” ecosystems, play critical ecological roles in the marine ecosystem and decline every year. The application of biochar in soil has been proposed as a potential soil amendment to improve soil quality and mitigate global climate change. The effects of biochar on soil bacterial activities are integrally linked to the potential of biochar in achieving these benefits. However, biochar has been rarely applied in marine ecosystems. Whether the application of biochar could work on the seagrass ecosystem remained unknown. In this study, we investigated the responses of sediment and rhizosphere bacterial communities of seagrass Thalassia hemprichii to the biochar addition derived from maize at ratios of 5% by dry weight in the soil during a one-month incubation. Results indicated that the biochar addition significantly changed the sedimental environment with increasing pH, total phosphorus, and total kalium while total nitrogen decreased. Biochar addition significantly altered both the rhizosphere and sediment bacterial community compositions. The significant changes in rhizosphere bacterial community composition occurred after 30days of incubation, while the significant variations in sediment bacterial community composition distinctly delayed than in sediment occurred on the 14th day. Biochar application improved nitrification and denitrification, which may accelerate nitrogen cycling. As a stabilizer to communities, biochar addition decreased the importance of deterministic selection in sediment and changed the bacterial co-occurrence pattern. The biochar addition may promote seagrass photosynthesis and growth by altering the bacterial community compositions and improving nutrient circulation in the seagrass ecosystem, contributing to the seagrass health improvement. This study provided a theoretical basis for applying biochar to the seagrass ecosystem and shed light on the feasible application of biochar in the marine ecosystem.

Graphical Abstract

Soil salinity regulation of soil microbial carbon metabolic function in the Yellow River Delta, China

The ecological consequences of soil salinization, one of the major causes of soil degradation worldwide, on soil carbon (C) emissions are well known, but less is known about the related microbial C metabolic function. We conducted laboratory incubation experiments on soil samples under a salt gradient at four levels (non-saline, low, medium, and high salinity soils) from coastal saline-alkaline soil of the Yellow River Delta, China, to assess the role of soil salinity in regulating C emissions and microbial abundance. We also evaluated the associations between salt content and the read number of microbial C metabolism genes by determining the soil metagenomes. We found that soil salinity was negatively related to soil C, nitrogen (N) content, C emissions, bacterial gene copy number, and the relative abundances of Actinobacteria, Thermoleophilia, and Betaproteobacteria, but positively related to the C/N ratio and the relative abundance of Gemaproteobacteria and Halobacteria. Increases in soil salinity correlated with decreases in carbohydrate metabolism and gene abundances of glycosyl transferases and glycoside hydrolases based on the metagenomic data. In contrast, the enzyme active genes of carbohydrate esterases and auxiliary activities were positively related to soil salinity. This study provides a clear understanding of the response of soil microbial communities and their C metabolic functions to soil salinity. We offer evidence that soil salinity has significant effects on microbial communities and soil C metabolic functions, resulting in an overall negative effect on soil C emissions.

Quantitative analysis of soil sustainability after applying stabilizing amendments in long-term Cd-contaminated paddy soils

Considering the biomagnification in food chains, cadmium (Cd) contamination in paddy fields has become concerning. The remediation of soil cadmium by the addition of amendments is a common agricultural practice. However, it remains ambiguous whether amendment use decreases soil environmental quality (SEQ) and sustainability. In this study, five compound amendments with different pH were utilized in long-term Cd-contaminated paddy soils. The SEQ of all treatments was quantitatively assessed according to a comprehensive evaluation mathematical model (Criteria Importance Through Inter-criteria Correlation (CRITIC)-Technique for Order Preference by Similarity to Ideal Solution (TOPSIS)), and the indicators involved in microbial functional gene (MFG) abundance, soil physicochemical and microbiological properties (CMP) and soil microbial function (N-related enzyme and transformation rate, N-ET) were measured. The results show that the SQE and remediation effect (expressed by the decrease in available Cd (A_Cd), %) in our treatments were alkaline > natural > acidic except for D alkaline treatment. The significant contradiction between soil SQE and remediation effect in D treatment attribute to its dose effects, which inhibiting microbial nitrogen assimilation and dissimilation and therefore counteracts the promoting effect of the decrease in A_Cd. Based on this discussion, three alkaline amendments (A, B and D) with similar effective remediation effect were employed in four other Cd-contaminated soils. Results indicated that both negative effect (D treatment) and promoting effect (A and B treatment) existed in the next 3 years.

Biochar and fertilizer improved the growth and quality of the ice plant (Mesembryanthemum crystallinum L.) shoots in a coastal soil of Yellow River Delta, China

Coastal soil is an important land reserve that may be used to alleviate the shortage of cultivated land; however, this soil is stressed by saline conditions and nutrient deficiency. Biochar offers the potential to reclaim coastal soil, but the response of plant growth to biochar addition in salt-affected soil is species-dependent. In this study, the response of ice plant (Mesembryanthemum crystallinum L.), an economically valuable halophyte that grows in the coastal soil of the Yellow River Delta, to wood chip biochar (WBC) either alone or in combination with chemical fertilizer was investigated using a 90-day pot experiment. The WBC enhanced the growth of ice plants in the coastal soil, but combining it with chemical fertilizer did not increase its effect. The nutritional quality of the plants was improved by the addition of WBC, regardless of whether chemical fertilizer was applied; moreover, WBC amendment enhanced photosynthesis and reduced the oxidative stress of the plants. The ameliorated soil properties (e.g., soil organic matter and water holding capacity) and increased contents of available macronutrients (e.g., P and K) and micronutrients (e.g., Mg, Mn, B and Zn) resulting from soil amendment with WBC may have contributed to the enhanced growth and quality of the ice plants. Additionally, in soil modified with WBC, an increased abundance of beneficial taxa (e.g., Erythrobacter, Sphingomonas and Lysobacter) and a shift in the microbial community may also have helped to improve the growth and quality of the ice plants. The results of our study provide useful information for developing a biochar-based technology to use in combination with valuable halophytes to reclaim degraded coastal soil and enhance food security.

Bacterial response to soil property changes caused by wood ash from wildfire in forest soils around mining areas: Relevance of bacterial community composition, carbon and nitrogen cycling

The different physical-chemical properties of the black ash (200-500 °C) and white ash (>510 °C) generated by wildfire may result in varied impacts on soil biological and abiotic indicators. Many studies have highlighted the environmental impacts of wood ash application due to its complex mixture of beneficial and detrimental compounds. However, few studies have compared the effect of black ash and white ash on soil, especially for the heavy metal polluted soil. In this study, we used the comparative analysis of parallel microcosm experiments to study the impacts of white ash and black ash on bioavailable heavy metals and metabolic potentials of microbial community. The results indicated that both white ash and black ash increased the concentration of soil bioavailable As and Cr, while the increasing trend of bioavailable As could be limited by Ca in the treatment of white ash. The addition of black ash could enhance the abundance of genes related to the Calvin cycle (CBB). Different kinds of wood ash inputs into soils could cause the differences in the microbial taxa for carbon fixation, as indicated by the dominance of different taxa for carbon fixation in white ash versus black ash treatments. Additionally, both white ash and black ash impaired dissimilatory nitrate reduction to ammonium (DNRA), nitrate assimilation and nitrification, while white ash enhanced denitrification.

Insights into the stabilization of landfill by assessing the diversity and dynamic succession of bacterial community and its associated bio-metabolic process

The distribution of bacterial community in an actual landfill was analyzed and the bioprocess involved in refuse degradation was clarified. The results showed that the degradation degree of refuse showed great differences with the landfill age, in which the contents of organic matter (OM) and total Kjeldahl nitrogen (TKN) in refuse as well as the chemical oxygen demand (COD) in leachate presented decreasing trends with increasing landfill age. The diversity of bacterial community increased first and then decreased with increasing landfill age. The main bacterial phyla involved in refuse degradation were Proteobacteria, Firmicutes and Bacteroidetes, among which, Proteobacteria had an absolute advantage with a relative abundance ranging of 66-78%. With increasing landfill age, the abundance of Firmicutes decreased gradually, while that of Bacteroidetes increased. Pseudomonas, Thiopseudomonas, Psychrobacter and Desemzia were the main genera. The distribution of bacterial community in samples with landfill ages of 0-1 and 1-3 years were greatly influenced by TKN and pH, respectively. Amino acid and carbohydrate metabolism were the main biological pathways according to the Kyoto Encyclopedia of Genes and Genomes (KEGG) database, and the biodegradation of xenobiotics as well as terpenoids and polyketides also accounted relatively high frequencies in the landfill. These results provide a better understanding of landfill microbiology and bioprocesses for landfill stabilization.

Seepage characteristics of three-layered landfill cover system constituting fly-ash under extreme ponding condition

A multi-layered final cover system is constructed over the landfill after it reaches its full capacity to minimize water ingress into the underlying hazardous waste. Three layered landfill cover are designed for areas experiencing very humid climatic conditions. Under the effects of climate change, the occurrences of extreme rainfall events become more frequent and this has resulted in catastrophic floods and hence extreme ponding. This study investigates the seepage characteristics of three-layered capillary barrier cover systems under an extreme ponding condition of 1.5 m water head, through detailed laboratory column tests and finite-element seepage analysis. Four 1.2 m-tall columns having different configurations (C1-C4) were studied. Fly ash (FA) was used to amend the surface and barrier layers in columns C2 and C4, in line with the novel concept of "waste protect waste". Spatiotemporal variations of volumetric water content of the four columns were monitored for three years continuously. With FA amendment in the surface layer and an inclusion of a 0.01 m thick geosynthetic clay liner between the drainage and barrier layers, the onset of basal percolation was significantly delayed until 700 days of ponding, compared to 115 days without FA amendment. Capillary flow dominated the gravitational flow and perched water table was formed as waterfront advanced from the drainage to barrier layers. Further seepage analysis considering a realistic humid climate boundary condition showed that all four configurations were successful in preventing basal percolation for 800 days.

Biochar Role in the Sustainability of Agriculture and Environment

The exercise of biochar in agribusiness has increased proportionally in recent years. It has been indicated that biochar application could strengthen soil fertility benefits, such as improvement in soil microbial activity, abatement of bulk density, amelioration of nutrient and water-holding capacity and immutability of soil organic matter. Additionally, biochar amendment could also improve nutrient availability such as phosphorus and nitrogen in different types of soil. Most interestingly, the locally available wastes are pyrolyzed to biochar to improve the relationship among plants, soil and the environment. This can also be of higher importance to small-scale farming, and the biochar produced can be utilized in farms for the improvement of crop productivity. Thus, biochar could be a potential amendment to a soil that could help in achieving sustainable agriculture and environment. However, before mainstream formulation and renowned biochar use, several challenges must be taken into consideration, as the beneficial impacts and potential use of biochar seem highly appealing. This review is based on confined knowledge taken from different field-, laboratory- and greenhouse-based studies. It is well known that the properties of biochar vary with feedstock, pyrolysis temperature (300, 350, 400, 500, and 600 °C) and methodology of preparation. It is of high concern to further investigate the negative consequences: hydrophobicity; large scale application in farmland; production cost, primarily energy demand; and environmental threat, as well as affordability of feedstock. Nonetheless, the current literature reflects that biochar could be a significant amendment to the agroecosystem in order to tackle the challenges and threats observed in sustainable agriculture (crop production and soil fertility) and the environment (reducing greenhouse gas emission).

Soilless revegetation: An efficient means of improving physicochemical properties and reshaping microbial communities of high-salty gold mine tailings

Soilless revegetation is a cost-effective and eco-friendly method for the ecological restoration of gold mine tailings. However, due to gold mine tailings are high-salty, alkaline and low-nutrient, little research has been done on soilless revegetation of gold mine tailings. The aim of study was to apply soilless revegetation to gold mine tailings, and investigate the changes of physicochemical properties and microbial communities of tailings after soilless revegetation. Six selected herbaceous plants (Melilotus officinalis, Xanthium sibiricum, Festuca elata, Zoysia japonica, Amaranthus tricolor L., Artemisia desertorum) grew well on the bare tailings, and their heights reached as high as 16.28 cm after 90 days. After soilless revegetation, tailings salinity dramatically dropped from 547.15 to 129.24 μS cm^-1, and pH went down from 8.68 to 7.59 at most. The content of available phosphorus (AP), available nitrogen (AN) and organic matter (OM) in tailings gradually improved, especially the content of AP and OM increased 53.36% and 52.58%, respectively. Furthermore, microbial metabolic activity and diversity in tailings obviously increased 70.33-264.70% and 1.64-13.97% respectively. The relative abundance of potential plant growth-promoting bacteria increased 1.40-3.05%, while the relative abundance of opportunistic pathogens and halophilic bacteria decreased 10.58-17.03% and 2.98-6.52% respectively. Such variations of microbial communities were beneficial for tailings restoration. This study provided insight into soilless revegetation and its impact on tailings microorganisms, which could be a new strategy for ecological restoration of gold mine tailings.

Long-term biochar addition alters the characteristics but not the chlorine reactivity of soil-derived dissolved organic matter

Biochar is widely and increasingly applied to farmlands. However, it remains unclear how long-term biochar addition alters the characteristics and chlorine reactivity of soil-derived dissolved organic matter (DOM), an important terrestrial disinfection byproduct (DBP) precursor in watersheds. Here, we analyzed the spectroscopic and molecular-level characteristics of soil-derived DOM and the formation and toxicity of DBP mixtures from DOM chlorination for two long-term (5 and 11 years) biochar addition experimental farmlands. As indicated by spectroscopic indices and Fourier transform ion cyclotron resonance mass spectrometry analyses, 11 years of biochar addition could increase the humic-like and aromatic and condensed aromatic DOM and decrease the microbial-derived DOM, while 5 years of biochar addition at the other site did not. The response of condensed aromatic dissolved black carbon did not increase with increasing cumulative biochar dose but appeared to be affected by biochar aging time. Despite the possible increase in aromatic DOM, biochar addition neither increased the reactivity of DOM in forming trihalomethanes, haloacetonitriles, chloral hydrates, or haloketones nor significantly increased the microtoxicity or genotoxicity of the DBP mixture. This study indicates that biochar addition in watersheds may not deteriorate the drinking water quality via the export of terrestrial DBP precursors like wildfire events.