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Effects of biochar and compost on microbial community assembly and metabolic processes in glyphosate, imidacloprid and pyraclostrobin polluted soil under freezethaw cycles
Pesticide misuse and overuse severely pollute agricultural soils, water, and crop yields, harming people and animals. This situation raises serious concerns about environmental pollution on a global scale. As an eco-friendly material for soil remediation, biochar can efficiently immobilize pesticides in the soil. Several studies have focused on the feasibility of biochar in remediating polluted soil. However, its influences during the remediation of pesticide-polluted soils remain indistinct. The present review illuminates the positive and negative influences of biochar on the dissemination of pesticides, the underlying mechanisms, the regulating factors, and critical considerations in the ongoing development of biochar for pesticide use. It also delineates the positive and negative impacts of biochar on pesticides in the soil, evaluates potential pitfalls based on recent research, and offers suggestions for prospective biochar applications crucial for remediating contaminated soil. This review reveals that the fate and types of pesticides, along with the physicochemical properties of soil and biochar types, can significantly influence the remediation of pesticide-polluted soil using biochar. Biochar has the potential to enhance the abundance of certain bacteria and the colonization of arbuscular mycorrhizal fungi, both of which play crucial roles in soil remediation. Biochar can also modify soil moisture, microbial communities, and other factors that impact the rate of pesticide degradation while simultaneously reducing other types of arbuscular mycorrhizal fungi. This review underscores the importance of thoroughly understanding the properties of biochar before its application to polluted soils. This review can serve as a basis for subsequent studies on the biochar-mediated remediation of contaminated soils.
The application of organic amendments (OAs) obtained from biological treatment technologies is a common agricultural practice to increase soil functionality and fertility. OAs and their respective pretreatment processes have been extensively studied. However, comparing the properties of OAs obtained from different pretreatment processes remains challenging. In most cases, the organic residues used to produce OAs exhibit intrinsic variability and differ in origin and composition. In addition, few studies have focused on comparing OAs from different pretreatment processes in the soil microbiome, and the extent to which OAs affect the soil microbial community remains unclear. This limits the design and implementation of effective pretreatments aimed at reusing organic residues and facilitating sustainable agricultural practices. In this study, we used the same model residues to produce OAs to enable meaningful comparisons among compost, digestate, and ferment. These three OAs contained different microbial communities. Compost had higher bacterial but lower fungal alpha diversity than ferment and digestate. Compost-associated microbes were more prevalent in the soil than ferment- and digestate-associated microbes. More than 80% of the bacterial ASVs and fungal OTUs from the compost were detected 3 months after incorporation into the soil. However, the addition of compost had less influence on the resulting soil microbial biomass and community composition than the addition of ferment or digestate. Specific native soil microbes, members from Chloroflexi, Acidobacteria, and Mortierellomycota, were absent after ferment and digestate application. The addition of OAs increased the soil pH, particularly in the compost-amended soil, whereas the addition of digestate enhanced the concentrations of dissolved organic carbon (DOC) and available nutrients (such as ammonium and potassium). These physicochemical variables were key factors that influenced soil microbial communities. This study furthers our understanding of the effective recycling of organic resources for the development of sustainable soils.
Acidification can seriously affect the growth of tea trees and the yield and quality of tea leaves. In this study, we analyzed the effects of acidification on the physicochemical properties, microorganisms and metabolites of tea rhizosphere soils with different pH values, and the results showed that with the increase of soil pH, the organic matter content, cation exchange capacity, microbial biomass carbon, microbial biomass nitrogen, microbial respiration intensity, bacterial number and actinomyces number in tea rhizosphere soil all showed an increasing trend, while the fungi number decreased. The results of soil metabolite analysis showed that 2376, 2377 and 2359 metabolites were detected in tea rhizosphere soil with pH values of 3.29, 4.74 and 5.32, respectively, and the number of similar compounds reached 2331, accounting for more than 98%. The results of soil metabolite content analysis showed that with the increase of soil pH, the total contents of metabolite of tea rhizosphere soil increased significantly. The results of correlation analysis between physicochemical indexes of soil and microorganisms and soil metabolites showed that physicochemical indexes of soil and microorganisms were significantly correlated with 221 soil metabolites, among which 55 were significantly positively correlated and 166 were significantly negatively correlated. Based on correlation interaction network analysis, 59 characteristic compounds were obtained and divided into 22 categories, among which 7 categories compounds showed a significant increasing trend with the increase of soil pH, while the other 15 categories compounds showed the opposite trend. Based on the functional analysis of characteristic metabolites, this study found that with the increase of soil pH in tea rhizosphere, the diversity and number of soil microorganisms increased, and the cyclic ability of C and N of tea rhizosphere soil was enhanced, which in turn might lead to the enhancement of resistance of tea tree and promote the growth of tea tree.
Context. The application of soil amendments to immobilise pesticide residues is a promising technology for meeting human health requirements, environmental protection and cost-effective remediation. Aims. This study aims to evaluate the effect of rice straw biochar (RB), rice straw compost (RC) and their mixtures at rates of 0.5% and 1.0% in pots, on the immobilisation of pesticides (such as atrazine, glyphosate and chlorpyrifos) in contaminated soil, using spectroscopy analysis under grown canola (Brassica napus L.) plants. Methods. Determination of immobilisation of pesticide residues by GC or HPLC and chemical properties of RB and RC and adding them at differentrates to the contaminated soil. Keyresults. The results showed that the addition of RB or RC alone or their mixtures led to a significant increase in the exchangeable Ca 2+ contents, organic matter (OM), cation exchange capacity (CEC), uptake of N, P and K and dry weight of canola plants. Pesticide concentrations decreased with increasing OM, CEC, and exchangeable Ca 2+ with the soil amended by RC and RB. The data indicated that adding RB at levels of 0.5% and 1.0% resulted in reductions in chloropyrifos by 43.2% and 63.1%, glyphosate by 32.8% and 77.3%, and atrazine by 21.9% and 72.2%, respectively, as compared to the control. Addition of (RC + RB) at 0.5% gave the highest pesticide immobilisation, followed (RC+RB) at 1.0%. Conclusion. These results indicate that the dominant mechanisms of pesticides immobilisation in the alkaline soils amended with RC and RB by FTIR and XRD analysis were π-π interaction, pore filling, hydrophobic effect, H-bonding, degradation as well as improvement of soil properties and dry yield of canola plants. Implications. Our results suggested the possibility of adding recycled rice straw in the form of compost or biochar to the contaminated soil to improve its properties, immobilise pesticides and increase its production capacity.
Atrazine, one of the most commonly used herbicides in the world, is of concern because of its frequent occurrence in various water bodies and the potential threat it constitutes to ecosystems. The transport of contaminants in seasonally ice-covered lakes is an important factor affecting the under-ice water environment, and changes in phase during ice growth and melting cause redistribution of atrazine between ice and water phases. To explore the migration pattern of atrazine during freezing and thawing, laboratory simulation experiments involving freezing and thawing were carried out. The effects of ice thickness, freezing temperature, and initial concentration on the migration ability of atrazine during freezing were investigated. The results showed that the relationship between the concentration of atrazine in ice and water during freezing was ice layer < water before freezing < water layer under the ice. Atrazine tended to migrate to under-ice water during the freezing process, and the intensity of migration was positively correlated with the ice thickness, freezing temperature, and initial concentration. During the thawing phase, atrazine trapped in the ice was released into the water in large quantities in the early stages. The first 20% of meltwater concentration was significantly higher than the average concentration in ice, with the highest case being 2.75 times the average concentration in ice. The results reported in this study are a useful reference for planning possible pollution control measures on such lakes during their freeze-thaw process.
Soil pesticide contamination induced by modern agriculture has become a serious global issue. Its uncontrolled and inefficient application is among the main reasons for their enrichment in plants and animals subsequently transferred to humans and providing a public health risk. Biochar as a renewable and economical carbonaceous material provides a natural solution for immobilizing pesticides and improving soil health. The biochar impact in agricultural contaminated soil is governed by various factors such as the physico-chemical properties of biochar, pyrolysis, soil conditions, and the application method, which can lead to significant gaps in the removal or mitigation of toxic substances. The current study summarizes the negative effects of pesticide use and the advantages of biochar according to other remediation techniques, succeeded by the mechanism and controlling factors on minimizing pesticide leaching and bioavailability in soil. In addition, the role of biochar on fundamental processes of adsorption, desorption, biodegradation, and leaching is discussed. Ultimately, the major future research regulation and key strategies that are fundamental for pesticide-contaminated soil remediation are proposed.
The herbicide glyphosate (N-phosphonomethylglycine) has been the most commonly applied herbicide worldwide for the past 40 years. This review presents and discusses the state of knowledge concerning groundwater contamination by glyphosate and its metabolite, aminomethylphosphonic acid (AMPA). A dataset of 48 reports and articles reporting on glyphosate and AMPA in groundwater worldwide was constructed from the published literature. Specific attention was given to the analysis of available studies on glyphosate and AMPA transport in groundwater to investigate groundwater contamination factors. The information presented in this review highlights detectable groundwater contamination in several countries, with many cases exceeding European groundwater quality standards. Both agricultural and non-agricultural applications of glyphosate can be significant sources of pollution, and proximity to agricultural fields is a significant risk factor. AMPA has two primary sources, glyphosate and amino polyphosphates, but very little information is available about the origin of AMPA detected in groundwater. Glyphosate and AMPA transport to groundwater can be significant in well-structured soils that are rich in macropores, where it generally occurs via preferential flow. An inverse relationship was highlighted between the groundwater depth and glyphosate and the occurrence and concentration of AMPA in groundwater; however, some discrepancies among the studies were identified. Heavy rainfall shortly after glyphosate application poses a high risk of its transport to groundwater. Seasonal trends in glyphosate and AMPA in groundwater, related to application timing, agronomic practices, and weather conditions, were also observed. Finally, risk-management measures are proposed.
Global concerns for desertification have focused on the slow recovery of extensive and expanding drylands following disturbance, which may be exacerbated by climate change. Biological soil crusts (biocrusts) are photosynthetic soil communities found in drylands worldwide, which are central to the stability and resilience of dryland ecosystems, but vulnerable to global change. Here we use multiple decade-long experiments to investigate the consequences of climate and land-use change on biocrusts and soil stability. Biocrusts recovered rapidly under ambient temperatures but warming interacted with the precipitation disturbance to halt recovery. Moreover, warming alone caused losses of mosses, lichens and soil stability. Our results present a new mechanism contributing to land degradation in drylands whereby warming drives a state shift in biocrust communities, which degrades soil stability. The synergistic effects of climate and land-use change co-occur globally and our results support projections of increased desertification and lowered dryland resilience under warming.
In this paper, several experiments were carried out to study the environmental behavior and influencing factors of glyphosate (PMG) in peach orchard ecosystem. The results of field experiments showed that PMG and its metabolite aminomethylphosphonic acid (AMPA) were detected in peach tree leaves and peach tree fruits, although PMG was only sprayed on the soil. The residues of PMG and AMPA in peach tree leaves were ~0.1 mg/kg and ~0.5 mg/kg and in peach tree fruits were ~0.01 mg/kg and 0.07-0.11 mg/kg, respectively. By conducting a series of laboratory simulation experiments, the environmental factors affecting the degradation of PMG were screened and evaluated. The results showed that PMG metabolized much faster in loess soil than red soil and black soil (with the DT50 of 11.6 days, 62.4 days, and 34.1 days, respectively). By analyzing the basic properties of the soil, we investigated the effects of pH, moisture content, organic matter (exogenous biochar) and ambient temperature using orthogonal experiments, and the results were further confirmed by microbial experiment. The results showed that alkaline conditions (pH = 7.8/9), high water content (25%) and microorganisms could promote the degradation of PMG. Sterile soil environment had a negative impact on the metabolic behavior of PMG to AMPA.
Biochar-induced changes in microbial communities are exclusively derived from the studies on the soil bacterial and fungal communities, and we lack an understanding of how biochar can affect taxonomic and functional communities of protists. Here, the short-term effects of two biochars originating from rice husk and poultry litter (hereinafter referred to as RH and PL, respectively) on taxonomic and functional community compositions of protists in a rice rhizosphere were studied using high-throughput sequencing. Soil physicochemical properties were differentially affected by the RH and PL amendments. The relative abundance of Stramenopiles, mainly oomycetes (Peronosporomycetes), was increased in the RH-amended soil, which was correlated with the increased total pore volume and C/N ratio. In the PL amended soil, the relative abundances of Amoebozoa, Alveolata, and Excavata were increased, and those increases were correlated with the enhanced pH and nutrient conditions. Among functional groups, the relative abundance of phagotrophic protists increased by the PL amendment, while the relative abundance of plant pathogens was decreased by both the RH and PL amendments. Network analysis indicated that phagotrophs were the keystone group and were sensitive to the biochar amendments. The keystone taxa in each biochar treatment were different: Cercozoa (Rhizaria) in control, Conosa (Amoebozoa) in RH, and Discoba (Excavata) in PL. The impact of biochar on protist communities correlated with its physicochemical properties, which depends on the source material.
Agricultural soil contamination in seasonally frozen land threatens food security. It is necessary to investigate the effects of freeze-thaw cycles on heavy metal bioavailability so as to select suitable immobilization agents. In this study, the soil was collected from a mid-latitude agricultural site in Liaoning Province, China, which was spiked with cadmium (Cd²⁺) and lead (Pb²⁺). Four immobilization treatments were set up, including (i) corn stover biochar, (ii) organic fertilizer, (iii) combined biochar and organic fertilizer, and (iv) the control group. The immobilized soils were subjected to 16 freeze-thaw cycles to temperatures of −10 °C, −20 °C, and −30 °C. It was found that freeze-thaw cycling increased the labile cadmium (Cd) and lead (Pb) content in the soil (i.e., exchangeable). The organic fertilizer treatment performed best in short-term immobilization, which was demonstrated by the amount of diethylenetriaminepentaacetic acid (DTPA) extractable lead (Pb) being 17.3–53.3% lower than that of the other treatments, and 7.2–31.5% lower for cadmium (Cd). Biochar, on the other hand, displayed better long-term performance under freeze-thaw cycling. This is probably because the biochar’s organic carbon content is relatively stable, and therefore, releases relatively little dissolved organic carbon (DOC) which could re-mobilize heavy metals. Furthermore, additional sorption sites are formed and the abundance of oxygen-containing functional groups increased when biochar breaks down during freeze-thaw cycles. Overall, the joint application of biochar and organic fertilizer had the greatest immobilization effect, which inhibited the cracking of soil aggregates, reduced the labile metal content, and displayed both short- and long-term immobilization effectiveness. It is suggested that combined biochar and organic fertilizer may offer an effective strategy for the sustainable agricultural management of cadmium (Cd) and lead (Pb) contaminated in seasonally frozen land.
The occurrence of emerging contaminants, such as: personal care products, medicines, pharmaceuticals, pesticides, and their transformation products in the environment is of concern for human health and aquatic ecosystems due to their high persistence, toxicity and potential to bioaccumulation. Among pesticides, the main attention and thus our focus is on neonicotinoids: acetamiprid, clothianidin, imidacloprid, thiacloprid and thiamethoxam, which are widely used classes of insecticides in agriculture. Determining the associated risk to humans and ecosystems from neonicotinoid insecticides requires detailed understanding of their fate and transport in the environment which is complex and includes diverse pathways and processes depending on environmental compartments in which they occur. This paper critically reviews the current state of the art about processes, parameters and phenomena influencing the fate of neonicotinoid insecticides in soil-water systems (i.e. soil and groundwater), and reveals existing knowledge gaps. Sorption, biodegradation, chemical transformations of neonicotinoid insecticides in the soil and leaching to the groundwater, as well as groundwater/surface water interactions are highlighted, as they determine their further migration from sources, through soils to groundwater systems and then to other environmental compartments posing ecological and human risks. A number of key knowledge gaps in fate of neonicotinoid insecticides in soil-water systems are identified, that concern mostly processes and pathways occurring in the groundwater, and require further research to assess the associated risk to humans and ecosystems.
In the current context, there is a growing interest in reducing the use of chemical fertilizers and pesticides to promote ecological agriculture. The use of biochar and plant growth-promoting rhizobacteria (PGPR) is an environmentally friendly alternative that can improve soil conditions and increase ecosystem productivity. However, the effects of biochar and PGPR amendments on forest plantations are not well known. The aim of this study is to investigate the effects of biochar and PGPR applications on soil nutrients and bacterial community. To achieve this goal, we applied amendments of (i) biochar at 20 t hm−2, (ii) PGPR at 5 × 1010 CFU mL−1, and (iii) biochar at 20 t hm−2 + PGPR at 5 × 1010 CFU mL−1 in a eucalyptus seedling plantation in Guangxi, China. Three months after applying the amendments, we collected six soil samples from each treatment and from control plots. From each soil sample, we analyzed several physicochemical properties (pH, electrical conductivity, total N, inorganic N, NO3−-N, NH4+-N, total P, total K, and soil water content), and we determined the bacterial community composition by sequencing the ribosomal 16S rRNA. Results indicated that co-application of biochar and PGPR amendments significantly decreased concentrations of soil total P and NH4+-N, whereas they increased NO3-N, total K, and soil water content. Biochar and PGPR treatments increased the richness and diversity of soil bacteria and the relative abundance of specific bacterial taxa such as Actinobacteria, Gemmatimonadetes, and Cyanobacteria. In general, the microbial composition was similar in the two treatments with PGPR. We also found that soil physicochemical properties had no significant influence on the soil composition of bacterial phyla, but soil NH4+-N was significantly related to the soil community composition of dominant bacterial genus. Thus, our findings suggest that biochar and PGPR amendments could be useful to maintain soil sustainability in eucalyptus plantations.
Background: Biochar amendments have been widely proposed as a conventional and efficient strategy to promote soil organic carbon (SOC) sequestration via negative priming. Unfortunately, the extent and biological mechanisms responsible for biochar-induced negative priming are still not fully understood. Despite traditional explanations focused on the environmental filtering mechanisms of biochar amendments on microbial biomass and community composition underlying the priming effect on SOC dynamics, whether and how a biochar-induced competitive interaction with keystone taxa determines SOC mineralization in natural ecosystems has been minimally explored.
Results: Here, we paid particular attention to the relationships between the diversity and network structure of soil bacterial and fungal communities, and SOC mineralization. A 3-year field experiment was conducted comprising five treatments: no fertilization, conventional fertilization, and conventional fertilization with three rates of biochar amendments. Biochar amendments considerably increased soil moisture capacity and pH, and subsequently shaped the composition and co-occurrence networks of soil bacterial and fungal communities. Importantly, network analysis revealed that the biochar amendments triggered the competitive interaction with putative keystone taxa in the bacterial and fungal networks. Structural equation modeling suggested that the competitive interaction with keystone taxa promoted bacterial and fungal diversity, and consequently reduced carbohydrate catabolism and soil metabolic quotient. Stable isotope probing incubations further provided consistent evidence of competition by keystone taxa with continual increases in the bacterial and fungal diversity under the biochar amendments.
Conclusions: We found that biochar-induced competition with keystone taxa stimulated the bacterial and fungal diversity, and consequently decreased SOC mineralization. The comprehensive understanding of the unexplored biological mechanisms underlying the biochar-induced negative priming may provide crucial implications for enabling SOC sequestration.
Core Ideas
Significantly more pesticides leached from frozen than from unfrozen soil columns.
Rapid breakthrough of pesticides indicated preferential flow in frozen soil.
A strong negative correlation between Kf and leaching was observed.
The effect of sorption properties is weaker in the presence of macropore flow.
Macropore flow may be less important for highly mobile or highly sorbed pesticides.
Field and laboratory studies show increased leaching of pesticides through macropores in frozen soil. Fast macropore flow has been shown to reduce the influence of pesticide properties on leaching, but data on these processes are scarce. The objective of this study was to investigate the effect of soil freezing and thawing on transport of pesticides with a range of soil sorption coefficients (Kf). To do this we conducted a soil column study to quantify the transport of bromide and five pesticides (2‐methyl‐4‐chlorophenoxyacetic acid, clomazone, boscalid, propiconazole, and diflufenican). Intact topsoil and subsoil columns from two agricultural soils (silt and loam) in southeastern Norway were used in this experiment, and pesticides were applied to the soil surface in all columns. Half the columns were then frozen (−3°C), and the other half were left unfrozen (4°C). Columns were subjected to repeated irrigation events where 25 mm of rainwater was applied during 5 h at each event. Irrigations were followed by 14‐d periods of freezing or refrigeration. Percolate was collected and analyzed for pesticides and bromide. Pesticide leaching was up to five orders of magnitude larger from frozen than unfrozen columns. Early breakthrough (<<1 pore volume) of high concentrations was observed for pesticides in frozen columns, indicating that leaching was dominated by preferential flow. The rank order in pesticide leaching observed in this study corresponded to the rank order of mean Kf values for the pesticides, and the results suggest that sorption plays a role in determining leaching losses even in frozen soil.
Unraveling the dynamics and driving forces of abundant and rare bacteria in response to glacial retreat is essential for a deep understanding of their ecological and evolutionary processes. Here, we used Illumina sequencing datasets to investigate ecological abundance, successional dynamics, and the co-occurrence patterns of abundant and rare bacteria associated with different stages of soil development in the Hailuogou Glacier Chronosequence. Abundant taxa exhibited ubiquitous distribution and tight clustering, while rare taxa showed uneven distribution and loose clustering along the successional stages. Both abundant and rare subcommunities were driven by different factors during assembly: the interactions of biotic and edaphic factors were the main driving forces, although less important for rare taxa than for the abundant ones. In particular, the redundancy analysis and structural equation modeling showed that soil organic C, pH, and plant richness primarily affected abundant subcommunities, while soil N and pH were most influential for rare subcommunities. More importantly, variation partitioning showed that edaphic factors exhibited a slightly greater influence on both abundant (7.8%) and rare (4.5%) subcommunities compared to biotic factors. Both abundant and rare bacteria exhibited a more compact network topology at the middle than at the other chronosequence stages. The overlapping nodes mainly belonged to Proteobacteria and Acidobacteria in abundant taxa and Planctomycetia, Sphingobacteriia, and Phycisphaerae in rare taxa. In addition, the network analysis showed that the abundant taxa exhibited closer relationships and more influence on other co-occurrences in the community when compared to rare taxa. These findings collectively reveal divergent co-occurrence patterns and driving forces for abundant and rare subcommunities along a glacier forefield chronosequence in the eastern Tibetan Plateau.
Crop pathogens and pests reduce the yield and quality of agricultural production. They cause substantial economic losses and reduce food security at household, national and global levels. Quantitative, standardized information on crop losses is difficult to compile and compare across crops, agroecosystems and regions. Here, we report on an expert-based assessment of crop health, and provide numerical estimates of yield losses on an individual pathogen and pest basis for five major crops globally and in food security hotspots. Our results document losses associated with 137 pathogens and pests associated with wheat, rice, maize, potato and soybean worldwide. Our yield loss (range) estimates at a global level and per hotspot for wheat (21.5% (10.1–28.1%)), rice (30.0% (24.6–40.9%)), maize (22.5% (19.5–41.1%)), potato (17.2% (8.1–21.0%)) and soybean (21.4% (11.0–32.4%)) suggest that the highest losses are associated with food-deficit regions with fast-growing populations, and frequently with emerging or re-emerging pests and diseases. Our assessment highlights differences in impacts among crop pathogens and pests and among food security hotspots. This analysis contributes critical information to prioritize crop health management to improve the sustainability of agroecosystems in delivering services to societies. © 2019, The Author(s), under exclusive licence to Springer Nature Limited.
Compositions of pollutant-catabolic consortia and interactions between community members greatly affect the efficiency of pollutant catabolism. However, the relationships between community structure and efficiency of catabolic function in pollutant-catabolic consortia remain largely unknown. In this study, an original enrichment (AT) capable of degrading atrazine was obtained. And two enrichments – with a better/worse atrazine-degrading efficiency (ATB/ATW) – were derived from the original enrichment AT by continuous sub-enrichment with or without atrazine. Subsequently, an Arthrobacter sp. strain, AT5, that was capable of degrading atrazine was isolated from enrichment AT. The bacterial community structures of these three enrichments were investigated using high-throughput sequencing analysis of the 16S rRNA gene. The atrazine-degrading efficiency improved as the abundance of Arthrobacter species increased in enrichment ATB. The relative abundance of Arthrobacter was positively correlated with those of Hyphomicrobium and Methylophilus, which enhanced atrazine degradation via promoting the growth of Arthrobacter. Furthermore, six genera/families such as Azospirillum and Halomonas showed a significantly negative correlation with atrazine-degrading efficiency, as they suppressed atrazine degradation directly. These results suggested that atrazine-degrading efficiency was affected by not only the degrader but also some non-degraders in the community. The promotion and suppression of atrazine degradation by Methylophilus and Azospirillum/Halomonas, respectively, were experimentally validated in vitro, showing that shifts in both the composition and abundance in consortia can drive the change in the efficiency of catabolic function. This study provides valuable information for designing enhanced bioremediation strategies.
Little is known about the effects of temperature and drying–rewetting on soil phosphorus (P) fractions and microbial community composition in regard to different fertilizer sources. Soil P dynamics and microbial community properties were evaluated in a soil not fertilized or fertilized with KH2PO4 or swine manure at two temperatures (10 and 25 °C) and two soil water regimes (continuously moist and drying–rewetting cycles) in laboratory microcosm assays. The P source was the dominant factor determining the sizes of labile P fractions and microbial community properties. Manure fertilization increased the content of labile P, microbial biomass, alkaline phosphomonoesterase activity, and fatty acid contents, whereas KH2PO4 fertilization increased the content of labile inorganic P and microbial P. Water regimes, second to fertilization in importance, affected more labile P pools, microbial biomass, alkaline phosphomonoesterase activity, and fatty acid contents than temperature. Drying–rewetting cycles increased labile P pools, decreased microbial biomass and alkaline phosphomonoesterase activity, and shaped the composition of microbial communities towards those with greater percentages of unsaturated fatty acids, particularly at 25 °C in manure-fertilized soils. Microbial C and P dynamics responded differentially to drying–rewetting cycles in manure-fertilized soils but not in KH2PO4-fertilized soils, suggesting their decoupling because of P sources and water regimes. Phosphorus sources, temperature, and water regimes interactively affected the labile organic P pool in the middle of incubation. Overall, P sources and water availability had greater effects on P dynamics and microbial community properties than temperature.
Freeze-thaw cycles are predicted to increase in cold temperate regions. The potential influence of the interactions of freeze-thaw cycles and agrochemicals on the release of Cd into river water is unknown. In this study, the interactions of freeze-thaw cycles and chlorpyrifos (FC) on Cd mobility in soils were analysed. The spatial variability of soil Cd under long-term intensive tillage in a freeze-thaw agro-system was also identified. The temporal variation of sediment Cd was detected based on analysis of the sediment geochemistry. The results showed that FC increased soil Cd mobility, with an increase of approximately 10% in CaCl2-extractable Cd. The increased mobile fractions of water-soluble and exchangeable Cd originated from the decreased fraction of Fe-Mn-oxide-associated Cd and organic matter-bound Cd. The total Cd content in the surface soil followed the zonally decreasing trend of dry land > paddy land > natural land. The Cd concentrations and sedimentation rates of the sediment core generally increased from 1943 to 2013 due to agricultural exploration and farmland irrigation system construction, indicating an increase of the Cd input flux into water. The results provide valuable information about the soil Cd transport response to the influence of climatic and anthropogenic factors in cold intensive agro-systems.
Drying-rewetting and freezing-thawing can drastically alter P availability in soil. We studied how these weather events affect microbial immobilisation/mobilisation of P on the four soil types from a climatic gradient with increasing annual mean temperatures and a progressive decrease in precipitation: Podzol, Phaeozem, Chernozem and Kastanozem. Soils were exposed to (1) optimal moisture and temperature, (2) drying-rewetting and (3) freezing-thawing. Soils were treated with a 33P spike immediately after rewetting or thawing to simulate P pulse. Thereafter, P immobilisation by soil microorganisms was estimated by direct fumigation and anion exchange membrane techniques. To ensure correct estimation of microbial P (Pmic), the conversion factors kP were determined individually for each soil by 33P labelling with the correction for 33P sorption and 31P–33P isotopic exchange. The membrane extraction minimised both sorption and isotopic exchange of P released with both sorption and isotopic exchange coefficients close to 0.9 irrespectively of the soil. Specific kP varied from 0.19 to 0.38. Pmic values followed the pattern freezing-thawing < drying-rewetting < optimal conditions, varying from 2.0 to 36.6 mg P kg−1. Intensive microbial immobilisation of 33P after rewetting (up to 41 %) demonstrated a conversion of dissolved P to Pmic potentially available for plant nutrition. Remarkably, no detectable microbial immobilisation of 33P was found in the freezing-thawing treatment. In contrast to drying, freezing decreased total Pmic by up to 7.5 times. Values of membrane-extractable 33P increased in the order drying-rewetting < control < freezing-thawing, and up to 77 % of added 33P was recovered in dissolved P forms after thawing, indicating the potential risk of P leaching after freezing-thawing events.
Straw return has been widely implemented to sequester soil organic carbon (SOC) and enhance soil quality in rice-wheat cropping systems, however, the mechanism through which it influences microbial assemblages into mediating biochemical metabolic pathways in soil remains ambiguous. This study aimed at investigating the composition and assembly of soil microbial communities and the soil metabolome prevailing across four straw return practices (control: no straw return; RR: rice-straw return; WR: wheat-straw return; DR: both rice- and wheat-straw return) during wheat cultivation on a rice-wheat rotation field. Straw return primarily altered the abundance of lipids (LL), organic acids (OA), organic nitrogen compounds, and benzenoids, with DR having a greater impact on soil metabolites than WR or RR. Besides being predominantly present in the lipid (LM) and amino acid (AAM) metabolic pathways, these differentially expressed metabolites (DEMs) were also dispersed throughout the nucleotide, xenobiotic, and secondary metabolite pathways. Straw return substantially elevated homogeneous selection in the order DR > WR > RR > control. The links of taxa to LM and AAM occupied by 64.9% in the DEMs-microbial taxa correlation network, with majority of taxa being derived from the keystone modules of the microbial network. Furthermore, these taxa potentially modulated variations in microbiota assembly by 27–45.1%, soil metabolites by 13.3–70.7%, and soil nutrient properties by 24.8–49.6%; and their removal evidently mitigated the natural connectivity of the microbial network. Structural equation modeling depicted that straw return exerted positive effects on LL and OA by regulating microbial assembly. Therefore, our results demonstrated that straw return drive microbial community assembly to dominate the taxa mediating soil LM and AAM for enhancing SOC sequestration and soil quality.
Global climate change has altered soil freeze‒thaw cycle events, and little is known about soil microbe response to and multifunctionality regarding freeze‒thaw cycles. Therefore, in this study, biochar was used as a material to place under seasonal freeze-thaw cycling conditions. The purpose of this study was to explore the ability of biochar to regulate the function of freeze-thaw soil cycles to ensure spring sowing and food production. The results showed that biochar significantly increased the richness and diversity of soil bacteria before and after freezing-thawing. In the freezing period, the B50 treatment had the greatest improvement effect (2.6% and 5.5%, respectively), while in the thawing period, the B75 treatment had the best improvement effect. Biochar changed the composition and distribution characteristics of the bacterial structure and enhanced the multifunctionality of freeze-thaw soil and the stability of the bacterial symbiotic network. Compared with the CK treatment, the topological characteristics of the bacterial ecological network of the B50 treatment increased the most. They were 0.89 (Avg.degree), 9.79 (Modularity), 9 (Nodes), and 255 (Links). The freeze-thaw cycle decreased the richness and diversity of the bacterial community and changed the composition and distribution of the bacterial community, and the total bacterial population decreased by 658 (CK), 394 (B25), 644 (B50) and 86 (B75) during the thawing period compared with the freezing period. The soil multifunctionality in the freezing period was higher than that during the thawing period, indicating that the freeze-thaw cycle reduced soil ecological function. From the perspective of abiotic analysis, the decrease in soil multifunctionality was due to the decrease in soil nutrients, enzyme activities, soil basic respiration and other singular functions. From the perspective of bacteria, the decrease in soil multifunctionality was mainly due to the change in the Actinobacteriota group. This work expands the understanding of biochar ecology in cold black soil. These results are conducive to the sustainable development of soil ecological function in cold regions and ultimately ensure crop growth and food productivity.
Neonicotinoid pesticides are the most widely used insecticides worldwide and have become a global environmental issue. Previous studies have shown that imidacloprid, the most used neonicotinoid, can negatively affect a wide range of organisms, including non-target insects, fish, invertebrates, and mammals. Imidacloprid can also accumulate and persist in soils, posing threats to the terrestrial ecosystem. However, we know little about one ecologically important group of organisms, the single-celled soil protists. In this study, we used a soil amoeba, Dictyostelium discoideum, to test whether and how imidacloprid affects the growth and development of soil amoebae. We provide the first empirical evidence that environmental concentrations of imidacloprid negatively impacted the fitness and development of soil amoebae. In addition, the adverse effects did not show a dose-response relationship with increased imidacloprid concentrations, where no significant difference was observed among the treatment groups. Further transcriptome analyses showed that imidacloprid affected amoeba's key DEGs related to phagocytosis, cell division, morphogenesis, and cytochrome P450. Moreover, soil amoebae show both conserved and novel transcriptional responses to imidacloprid. In conclusion, this study has expanded the non-target list of imidacloprid from animals and plants to single-celled protists, and we believe the impact of neonicotinoid pesticides on the microbiome is significantly underestimated and deserves more studies.
Biochar aging affects the stability of soil carbon. Analyzing the effect of biochar on soil organic carbon (SOC) forms and their relations with microbial community assembly and carbon metabolism with time is helpful for soil carbon sequestration (by adapting the farm management approach). Four treatments with no, low, medium, and high biochar application rates (0 %, 1 %, 2 %, and 4 % of the total dry weight of topsoil before winter wheat planting, abbreviated as control, LB, MB, and HB, respectively) were conducted in the field. The SOC and particulate organic carbon positively correlated with the biochar application rate. Biochar decreased readily oxidizable carbon (P < 0.05) after 8 months of application compared to the control; however, the difference disappeared with time. Biochar increased dissolved organic carbon (DOC) but had no effect on water- soluble organic carbon (WSOC); DOC and WSOC decreased with time. Furthermore, LB and HB stabilized the bacterial alpha diversities with time. Based on high-throughput sequencing, HB reduced the relative abundance of Actinobacteriota but increased that of Acidobacteria (P < 0.05) after 12 months of biochar application. Time-wise, the bacterial community assembly was determined by deterministic processes that were significantly affected by the available nitrogen, DOC, or WSOC. Compared with the control, biochar decreased bacterial links and improved bacterial metabolism of phenolic acids and polymers with time, as evidenced by Biolog EcoPlates. Structural equation modeling revealed that the contribution of bacterial assembly processes to carbon metabolism changed with time. Microbial carbon metabolism was most positively influenced by differences in the composition of bacterial specialists. These findings reinforced that changes in soil labile organic carbon were time-dependent but not necessarilty affected by the biochar application rate.
The problem of potentially toxic elements (PTEs) in farmland is a key issue in global pollution prevention and control and has an important impact on environmental safety, human health, and sustainable agricultural development. Based on the climate background of high–latitude cold regions, this study simulated freeze–thaw cycles through indoor tests. Different initial conditions, such as biochar application rates (0%, 1%, 2%) and different initial soil moisture contents (15%, 20%, 25%), were set to explore the morphological changes in cadmium (Cd) and lead (Pb) in soil and the response relationship to the changes in soil physicochemical properties. The results indicate that soil pH decreases during freeze–thaw cycles, and soil alkalinity increases with increasing biochar content. Freeze–thaw cycles caused the total amount of PTEs to have a U–shaped distribution, and the amount of PTEs in the soluble (SOL) and reducible (RED) fraction increased by 0.28–56.19%. Biochar reduced the amount of Cd and Pb migration in the soil, and an increase in soil moisture content reduced the availability of Cd and Pb in the soil. Freezing and thawing damaged the soil structure, and biochar reduced the fractionation of small particle aggregates by enhancing the stability of soil aggregates, thereby reducing the soil's ability to adsorb Cd and Pb. In summary, for farmland soil remediation and pollution control, the application of biochar has a certain ability to optimize soil properties. Considering the distribution of PTEs in the soil and the physicochemical properties of the soil, the application of 1% biochar to soil with a 20% moisture content is optimal for regulating seasonally frozen soil remediation.
Biochar has been widely used as a soil conditioner, but research on the mid-and long-term effects of biochar on soil structure and soil erosion is still seriously lacking. To investigate the effects of mid- and long-term applications of biochar on soil improvement and soil erosion, a 4-year experiment was carried out on a field runoff plot of 3° sloping farmland in the black soil region of Northeast China. By examining the influence of different biochar application amounts (0, 25, 50, 75, and 100 t ha⁻¹) on annual runoff, annual soil erosion, soil water retention curves, unsaturated hydraulic conductivity and unsaturated water diffusivity over four consecutive years, the optimal biochar application rate was determined. The results showed that the biochar application amount, year and their interaction imposed significant effects on soil structure, annual runoff, annual soil erosion, and moisture characteristic parameters. When the water content exceeded a certain value (0.28 cm³ cm⁻³), biochar improved the soil hydraulic conductivity. biochar inhibited the horizontal diffusion of water, while Pearson correlation analysis indicated that soil structure improvement encouraged soil water holding capacity enhancement and prevented soil erosion. Based on the analysis of the soil structure and soil erosion during the four-year period, the best biochar application rate for water and soil improvement of the sloping farmlands in the black soil area was proposed, namely, biochar application at 50 t ha⁻¹ for two consecutive years. The research results provide practical application for combat soil erosion of sloping land.
Glyphosate can be degraded by soil microorganisms rapidly and is impacted by temperature and soil properties. Enhanced temperature and total organic carbon (TOC) as well as reduced pH increased the rate of ¹³C3¹⁵N-glyphosate conversion to CO2 and biogenic non-extractable residues (bioNERs) in a Haplic Chernozem (Muskus et al., 2019) and in a Humic Cambisol (Muskus et al., 2020). To date; however, the combined effect of temperature and TOC or pH on microbial community composition and glyphosate degraders in these two soils has not been investigated. Phospholipid fatty acid [PLFA] biomarker analysis combined with ¹³C labeling was employed to investigate the effect of two soil properties (pH, TOC) and of three temperatures (10 °C, 20 °C, 30 °C) on soil microorganisms. Before incubation, the properties of a Haplic Chernozem and a Humic Cambisol were adjusted to obtain five treatments: (a) Control (Haplic Chernozem: 2.1% TOC and pH 6.6; Humic Cambisol: 3% TOC and pH 7.0), (b) 3% TOC (Haplic Chernozem) or 4% TOC (Humic Cambisol), (c) 4% TOC (Haplic Chernozem) or 5% TOC (Humic Cambisol), (d) pH 6.0 (Haplic Chernozem) or pH 6.5 (Humic Cambisol), and (e) pH 5.5 for both soils. All treatments were amended with 50 mg kg⁻¹ glyphosate and incubated at 10 °C, 20 °C or 30 °C. We observed an increase in respiration, microbial biomass and glyphosate mineralization with incubation temperature. Although respiration and microbial biomass in the Humic Cambisol was higher, the microorganisms in the Haplic Chernozem were more active in glyphosate degradation. Increased TOC shifted the microbiome and the ¹³C-glyphosate degraders towards Gram-positive bacteria in both soils. However, the abundance of ¹³C-PLFAs indicative for the starvation of Gram-negative bacteria increased with increasing TOC or decreasing pH at higher temperatures. Gram-negative bacteria thus may have been involved in earlier stages of glyphosate degradation.
Soil amendments have been extensively used to remediate heavy metal contaminated soils by immobilizing or altering edaphic properties to reduce the bioavailability of heavy metals. However, the potential influences of long-term soil amendments applications on microbial communities and polluted soil health are still in its infancy despite that have been applied for decades. We used amplicon sequencing and q-PCR array to characterize the root-associated microbial community compositions and rhizosphere functional genes in a five-year field experiment with consecutive application of four amendments (lime, biochar, pig manure, and a commercial Mg-Ca-Si conditioner). Compared with the control, soil amendments reduced the available Cd (CaCl2 extractable Cd) in soils and strongly affected bacterial community compositions in four root-associated niches. Five rare keystone bacterial species were found belonging to the family Gallionellaceae (1), Haliangiaceae (1), Anaerolineaceae (2), and Xanthobacteraceae (1), which significantly correlated with soil pH and the functional genes nifH and phoD. Random forest analysis showed that rhizosphere soil pH and microbial functions, and root-associated keystone bacterial community compositions mainly influenced the Cd concentrations in rice grains. Altogether, our field data revealed five-year consecutive application of soil amendments regulated root-associated microbial community assembly and enhanced microbial functions, thereby improved rhizosphere health of Cd-contaminated soils.
Soil microorganisms play key roles in agricultural ecosystems. However, little is known about their dynamic diversity patterns and community assembly processes, especially in the rare microbial biosphere in agriculture systems. In this study, we determined the responses of diversities and assembly processes of abundant and rare bacterial and fungal subcommunities to agricultural practice (i.e. cover crop) in a semiarid orchard soil by using 16S and ITS rRNA gene sequencing. We found that the community structures of abundant and rare taxa exhibited a similar response to cover crop or growth periods. Growth periods significantly changed the bacterial and fungal subcommunities structure. Only the fungal subcommunities structure was affected by cover crop. The community assembly of abundant and rare fungi was respectively dominated by stochastic process and deterministic process and less affected by cover crop and growth period. For abundant bacteria, the assembly process was dominated by heterogeneous and undominated processes, and the importance of heterogeneous selection process was increased by cover crop at setting and maturing period. The assembly process of rare bacterial community was dominated by a homogeneous selection and the relative importance of dispersal limitation was increased at maturing period. We also found that the assembly processes of abundant taxa were significantly related to the soil DON, NH4⁺-N, NO3–-N and pH, while the assembly processes of rare taxa were significantly related to the soil DOC, AP and SOC. Our results provide new insights into the formation of the microbial community in orchard soil under a cover crop, especially the seasonal succession of abundant and rare bacterial and fungal subcommunities.
Soil microbial community diversity and composition are responsive to biochar application. However, the impacts of biochar application on soil microbial community structure and interactions in different aggregate fractions are poorly understood. We conducted a 3-year field trial involving biochar application to black soil in northeastern China. Four biochar treatments were applied: 0 (B0, control), 10 (B10), 30 (B30) and 50 (B50) t ha⁻¹ biochar. Compared to the B0 treatment, biochar application significantly decreased the diversity of bacterial and fungal communities. In addition, biochar application significantly increased the relative abundances (RAs) of Bacteroidetes and Proteobacteria and significantly decreased those of Actinobacteria, Chloroflexi, Planctomycetes and Verrucomicrobia. Moreover, the B30 and B50 treatments significantly increased and decreased the RA of Nitrospirae, respectively. Moreover, the RA trends of Acidobacteria, Nitrospirae and Planctomycetes among different aggregate fractions was mega-aggregates (ME; > 2 mm) > macroaggregates (MA; 0.25–2 mm) > microaggregates (MI; < 0.25 mm); the RAs of Basidiomycota and Glomeromycota in ME were higher than those in MA and MI. The RA of Ascomycota in MI was the highest among the different aggregate fractions. The co-occurrence networks showed that the B30 treatment enhanced microbial interactions in terms of the number of links, average degree, and modularity, while the B50 treatment reduced these interactions. Additionally, co-inertia analysis demonstrated that the microbial interactions in ME were enhanced by biochar application. Thus, an appropriate biochar application (e.g., 30 t ha⁻¹ used in the present study area) can enhance soil microbial interactions, especially in ME.
Neonicotinoids have been previously detected in Iowa surface waters, but less is known regarding their occurrence in groundwater. To help fill this research gap, a groundwater study was conducted in eastern Iowa and southeastern Minnesota, a corn and soybean producing area with known heavy neonicotinoid use. Neonicotinoids were studied in alluvial aquifers, a hydrogeologic setting known to be vulnerable to surface-applied contaminants. Groundwater samples were analyzed from 40 wells for six neonicotinoid compounds (acetamiprid, clothianidin, dinotefuran, imidacloprid, thiacloprid, thiamethoxam), and sulfoxaflor. Samples were analyzed using liquid chromatography tandem mass spectrometry (LC/MS/MS) with both direct aqueous injection and solid phase extraction methods. Neonicotinoids were prevalent in the alluvial aquifers with 73% of the wells having at least one neonicotinoid detection. Clothianidin (68%, max: 391.7 ng/L) was the most commonly detected, followed by imidacloprid (43%, max: 6.7 ng/L) and thiamethoxam (3%, max: 0.2 ng/L). Acetamiprid, dinotefuran, sulfoxaflor, and thiacloprid were not detected during the study. The solid phase extraction method was more sensitive than direct aqueous injection, where only clothianidin detected in 23% of samples. SPE is the preferred method for detecting low concentrations of hydrophilic pesticides in water. This study documented that the combination of heavy chemical use overlying a hydrogeologic setting vulnerable to surface applied contaminants leads to transport of neonicotinoids into an important groundwater resource.
The role of soil organic nitrogen (e.g., amino acids) in regulating soil microbial community has not been well documented, which is much different from that of soil organic carbon. Feather-based compost (FBC) is rich in amino acids that can enhance soil life and microbial activity. Therefore, this study was designed to evaluate the possible role of amino acids in FBC in regulating soil microbial community. In pot experiment, FBC was applied to lettuce (Lactuca sativa) grown in an infertile subtropical soil. Soil chemical property, enzyme activity, and hydrolysable amino acids were analyzed, and microbial community was characterized with polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis. FBC significantly increased plant biomass, soil available nutrient contents, and enzyme activity. Thirteen kinds of amino acids were detected in soil, and FBC significantly increased the contents of 12 kinds of amino acids, with 5 absent in soils without FBC application. Both amino acids and soil chemical property were significantly correlated with microbial community and soil enzyme activity, and their contributions to the changes in microbial community and soil enzyme activity were comparable. Phenylalanine, leucine, and glutamate were the top 3 kinds of amino acids structuring microbial community. Our results suggest that FBC greatly promoted plant growth probably via the regulatory effects of amino acids on soil microbial community, which sheds light on the application of amino acid-rich compost in agricultural production.
Uptake of residual pesticides in a soil by a certain crop plant may be governed by their physicochemical properties. Uptake and translocation of pesticides (imidacloprid, acetamiprid, tricyclazole, azoxystrobin, tebuconazole and difenoconazole) with the octanol/water partition coefficient (log Kow) ranging from 0.57 to 4.36 were investigated in soil with maize as a model plant. The results show that all tested pesticides in soil were uptaken by maize with accumulation amount of 27.73, 17.75, 18.96, 12.56, 10.66 and 2.13 μg for imidacloprid, acetamiprid, tricyclazole, azoxystrobin, tebuconazole and difenoconazole at 14 d, respectively. The accumulation amount was negatively correlated with adsorption coefficients and positively correlated with pesticide concentration in in situ pore water (CIPW). Root bioconcentration factor varied widely from 0.61 for imidacloprid to 974.64 for difenoconazole was positively correlated with log Kow and molecular weight but negatively with water solubility. Conversely, translocation factor varied from 0 for difenoconazole to 1.64 for imidacloprid was negatively correlated with log Kow but positively with water solubility. It determined that uptake, accumulation and translocation of the pesticides in soil by maize are governed by their physicochemical properties, especially log Kow. CIPW is an appropriate candidate to evaluate the accumulation of pesticides in maize from soil.
Exposure assessment of pesticides has substantially improved over time, with methods that now include a combination of advanced analytical techniques and fate/transport models to evaluate their spatio-temporal distribution. However, current regulatory environmental risk assessment considers thresholds from laboratory studies completed under standardized conditions that do not reflect environmental dynamics. Using the GUTS model framework, we predicted the impact of time-varying pesticide exposures on the survival of gammarids in a small agricultural stream. LP50 values were used as an additional metric for assessing risks (defined in GUTS as the multiplication factor applied to the concentration time series to induce 50% mortality by the end of exposure). Although real-case exposures to individual pesticides were predicted to produce little to no impact on survival, the LP50 values indicate acute (LP50≤100) and/or chronic (LP50≤10) toxicities for azoxystrobin, chlorpyrifos, diazinon, and imidacloprid, while risk to propiconazole exposure was considered very low (LP50≫100). Finally, the model was extended to reflect mixture toxicity via concentration addition. It predicted risks under acute and chronic exposures to organophosphates and neonicotinoids. Given that gammarids are simultaneously exposed to multiple chemicals and other stressors throughout their lifetime, a decline in survival probabilities due to chemical stress can likely influence their overall fitness. We recognize that some assumptions require validation, but our work included a level of realism that can assist risk managers when evaluating the cumulative consequences of chemical exposure. .
Application of biochar technology in the remediation of organic contaminated soils has drawn growing interest in recent years. In this study, sorption and degradation of two typical neonicotinoid insecticides, imidacloprid (IMI) and clothianidin (CLO) in Chinese typical paddy soil and red soil amended with six kinds of biochars were investigated. The results showed that surface area (SA), pH, total organic carbon and dissolved organic carbon (DOC) of the two soils all increased after biochar amendment, while H/C decreased. With biochar pyrolyzing temperature (PT) increasing from 300 °C to 700 °C, the sorption of the two insecticides on biochar–soil mixtures increased by more than 4.3-fold, due to the increasing SA and decreasing H/C. The acidic pH of the two tested soils also favored the enhanced sorption of the insecticides by removing the ash on biochar. The amendment of low-PT (300 °C) biochar promoted the biodegradation of IMI and CLO by 11.3–41.9% via providing more DOC and available N for microorganisms, while inhibiting the chemical degradation. Oppositely, the high-PT (500–700 °C) biochars inhibited the biodegradation of the insecticides by decreasing their bioavailability and promoted the chemical degradation by providing mineral active groups, and generating ·OH and other free radicals. In addition, soil type also affected the effects of biochar remediation. The highest 60-day degradation extent was achieved for CLO (90.5%) and IMI (81.4%) in paddy soil by adding biochar derived from pig manure at 700 °C PT. In summary, the effect of biochar on the fate of organic contaminants in soil is a comprehensive result involving several processes and a systematic study considering the type and property of biochar and soil is needed to optimize biochar technology.
Polycyclic aromatic hydrocarbon (PAH) contamination in agricultural soils poses serious stress to the soil microbiome. With the broad application of biochar, however, the co-effects of biochar and plant roots on the bacterial responses to PAH stress remain unclear. Here, the effects of biochar and the rhizosphere on bacterial community structure and functions were analyzed by coupling enzyme activity tests, high-throughput sequencing, and soil metabolomics. The contents of available nutrients and dissolved organic carbon, enzyme activities, and carbon metabolism functions were improved by biochar and plant roots. With the combined effects of biochar and plant roots, sucrose and starch metabolism was mainly impacted, and the soil metabolite diversity decreased. There was a strong co-occurrence network among soil properties, bacterial members, and metabolites in the biochar-amended and rhizosphere soils, favoring bacterial resistance to PAH stress, and consequently, PAH removal. In light of the above results, we suggest that biochar application can efficiently improve bacterial functions in rhizosphere soil, and our results facilitate the development of in situ remediation programs in soil contaminated with PAHs.
This is the first large scale study of fate of the glyphosate (GLP) and its metabolites, (AMPA, N-acetyl glyphosate, N-acetyl AMPA, sarcosine and glycine) monitored by LC/MS/MS. The laboratory trials of behavior of GLP in two types of agricultural soil were performed. Soil (S), soil enriched with sewage sludge (S + SL), soil with Pseudomonas fluorescens (S + P) and soil enriched with sewage sludge and P. fluorescens (S + SL + P) was treated with Roundup 360 SL under controlled conditions. The presence of metabolites was depended on the soil type and enrichment with sludge or bacteria. The GLP and its soil metabolites caused increase of microorganisms association in comparison to control. We assumed that P. fluorescens and sewage sludge influence on time of GLP dissipation. Moreover, GLP degradation in presence of P. fluorescens and sewage sludge is carried out in different metabolic pathways compared to control (S + GLP). Furthermore, presence of particular GLP metabolites is related to different metabolic pathways and is connected with P. fluorescens and sewage sludge occurrence in soil. Additionally, P. fluorescens and sewage sludge stimulate enzymatic activity of soils.
Adding biochar (BC) to soils is proposed to enhance carbon sequestration in agricultural soils. However, there is limited knowledge regarding the effects of the interactions between BC and nitrogen (N) on soil organic carbon (SOC) mineralization at an interannual scale. We conducted a three-year field experiment to systematically reveal the impacts of BC combined with N fertilizer on a silty clay soil, including its physicochemical properties, soil respiration characteristics and microbial community. BC applied once at 0, 20 and 40 t ha⁻¹ (B0, B1 and B2, respectively) was combined with three N fertilization levels (0, 120 and 240 kg N ha⁻¹; N0, N1 and N2, respectively). Only winter wheat (Triticum aestivum L.) was cultivated, and it was cultivated in a winter wheat-summer fallow crop system. BC application persistently increased the SOC content by 36.3–91.6% over three years. Several soil parameters were also improved by BC combined with N after one year, such as bulk density, NO3- and available P content. Compared with its values with B0 treatments with N1 or N2, the total soil CO2 emitted decreased by 6.7–8.9% in response to BC combined with N1 but increased by 5.9–7.5% in response to BC combined with N2. B1N1 not only significantly increased microbial biomass but also decreased qCO2. In addition, B1N1 in particular increased the relative abundances of members of the microbial population associated with increased microbial C use efficiency, such as Rhizopus and Helotiaceae. However, B2N1 and B2N2 strongly disturbed the soil microbial ecosystem; moreover, the lowest alpha diversity of the bacterial community was observed in B2N2 soils. In summary, adding BC at a high rate to N-fertilized soil strongly disturbs the soil microbial ecosystem and reduces the C-sequestering potential of soil, while B1N1 treatment is recommended to enhance soil C sequestration and improve soil fertility under dryland farming.
The increased use of plastic films and pesticides on agricultural soil leads to the accumulation of plastic debris and pesticide residues in soil. This accumulation has become a serious environmental issue, as it threatens life of earthworms, inhibits the enzyme activities and microbial diversity, and contributes to the loss of soil microbial carbon and nitrogen. However, little information is available regarding the effects of pesticides on soil dissolved organic matter (DOM). It is also unknown how plastic debris, especially small-sized particles called microplastics, influences the effects of pesticides on soil DOM. In this study, we performed a 30-day soil incubation experiment. Three levels of the common herbicide glyphosate were applied to soil: 0 (control, CK), 3.6 kg ha⁻¹ (G1) and 7.2 kg ha⁻¹ (G2). We also tested four levels of glyphosate and microplastics (homopolymer polypropylene powder) co-addition: 3.6 kg ha⁻¹ + 7% (w/w) (M1G1), 3.6 kg ha⁻¹ + 28% (w/w) (M2G1), 7.2 kg ha⁻¹ + 7% (w/w) (M1G2), and 7.2 kg ha⁻¹ + 28% (w/w) (M2G2). Glyphosate addition slightly increased soil fluorescein diacetate hydrolase (FDAse) and phenol oxidase (PO) activities. Although the glyphosate addition significantly promoted the accumulation of dissolved organic phosphorus (DOP) within the first 14 days, the M2 treatment decreased DOP at day 30. M2G1 and M2G2 increased soil FDAse activity and promoted the accumulation of DOC and DOP relative to G1 and G2 respectively while M1G1 and M1G2 benefited DON accumulation. Our results highlighted that the interaction between glyphosate and low microplastics content negatively affected DOC and DOP dynamics, leading to the loss of bioavailable C and P loss. The interaction between glyphosate and high content microplastics negatively affected DON compared with glyphosate addition, possibly decreasing DON.
Benzophenone-3 (BP-3) is extensively applied in sunscreens and some other related cosmetic products. It is necessary to efficiently and safely remove BP-3 from environments by application of various treatment technologies. However, to the authors' knowledge, BP-3 biodegradation by a single bacterial strain has not been reported before. In this study, a Gram-negative aerobic bacterium capable of degrading BP-3 as a sole carbon source was isolated from a municipal wastewater treatment plant and classified as Methylophilus sp. FP-6 according to BIOLOG GEN III and 16S rDNA analysis. Methanol was chosen for further experiments as a co-metabolic carbon source to enhance the microbial degradation efficiency of BP-3. Orthogonal and one-way experiments were all performed to investigate the optimal culture conditions for degradation of BP-3 by Methylophilus sp. FP-6. The degradation rate of BP-3 reached about 65% after 8 days of incubation with strain FP-6 under optimal culture conditions. The half-life (t1/2) of BP-3 biodegradation by strain FP-6 was estimated as 2.95 days according to the BP-3 degradation curve. The metabolite intermediates generated during the BP-3 degradation process were analyzed by LC-MS/MS and three metabolite products were identified. According to the analysis of metabolic intermediates, three pathways for degradation of BP-3 by strain FP-6 were proposed. The results from this study gave first insights into the potential of BP-3 biodegradation by a single bacterial strain.
Agricultural chemicals affect the daily life of food production. However, the abuse of pesticides led to the damage to the environment. Pyraclostrobin (PYR) is commonly used strobilurin fungicide which inhibits fungal respiration through mitochondrial cytochrome-b and c1 inhibition. There is increasing concerns that PYR may adversely impact the environment. Although impacts on ecological receptors have been detailed, little information is available regarding the toxicological impact of PYR on soil microbial community dynamics and functioning. Understanding the potential impact on soil microbial populations is important. The activity of enzymes (urease, dehydrogenase, and β-glucosidase) and diversity of microbial community structure using high-throughput 16S rRNA sequencing were evaluated at different soil-PYR concentrations (0.1, 1.0, and 2.5 mg/kg) over a 48 day exposure period. Urease activity remained stable in general. Pyraclostrobin inhibited dehydrogenase activity during the exposure period. The β-glucosidase activity was inhibited on day 28 and induced on day 48 at 1.0 and 2.5 mg/kg. The genera Gp6, Exiguobacterium, Gp4, and Gemmatimonas were both the dominant genera and significantly changed genera. Pyraclostrobin had different level of influence on soil microbes containg their enzyme activity and community structure. The purpose of the current study was to examine the impact of PYR addition on soil enzymes as an indicator of soil health and to have complementary data on the impact of microbial populations. Furthermore, the study may also be the guide for further rational pesticide selection.
In recent years, pyraclostrobin has been widely used as a fungicide. However, pesticides remain in soil and water, potentially causing irreversible damage to non-target organisms. Thus, the present study investigated the toxicity of different pyraclostrobin concentrations (0, 0.1, 1.0, and 2.5 mg/kg) on earthworms (Eisenia fetida). On days 7, 14, 21, and 28, reactive oxygen species (ROS), superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (POD), glutathione-S-transferase (GST), and malondialdehyde (MDA) levels as well as DNA damage were evaluated. The ROS content under 0.1 mg/kg pyraclostrobin treatment first increased and later returned to the control level. High concentrations of pyraclostrobin (1.0 and 2.5 mg/kg) led to excessive ROS during the experiment. Enzyme activities and MDA contents in the experimental groups first increased and then decreased. Except for POD activity with 0.1 mg/kg pyraclostrobin treatment, SOD, POD, and GST activities under pyraclostrobin treatment were inhibited on day 28. However, CAT activities and MDA contents in the experimental groups were similar to control levels on day 28. DNA damage was promoted with increasing concentrations of pyraclostrobin. On days 21 and 28, DNA damage in earthworms treated with 0.1 mg/kg pyraclostrobin decreased. However, DNA damage in earthworms treated with 1.0 and 2.5 mg/kg pyraclostrobin rose slowly after the 14th day. In summary, pyraclostrobin can break the dynamic balance of ROS in the organism, which can affect the antioxidant defense system and ultimately cause DNA damage.
Waste management is a continuous global need. To minimize problems arising from municipal solid waste (MSW) disposal, composting has emerged as a simple alternative for the organic fraction of the waste. The composting process generates organic composts with a high metal retention capacity for potentially toxic elements (PTE). Thus, our objective was to examine how different composting methods (windrow composting, wire mesh composting bin, and passively aerated static pile composting) affect the final product, and how the characteristics of the generated composts influence their adsorption capacity for the lead (Pb), zinc (Zn) and cadmium (Cd) elements from mining waste. Therefore, the physical and chemical properties of Brazilian composts were investigated, as well as their adsorption capacities, through batch equilibrium tests with Pb, Zn and Cd in single-element solutions. All composts revealed promising adsorption characteristics, including a near-neutral pH (6.4-7.7); a negative ΔpH (-0.4 to -1.0); oxidizing conditions (Eh between +267.67 and + 347.00 mV); a considerable presence of organic matter (193.92-418.70 g kg-1); a substantial (albeit very varied) cation exchange capacity (29.00-75.00 cmolc kg-1); and significant porosity (pore volume between 0.01113 and 0.05400 cm3 g-1). These results showed that the composts share similar intrinsic characteristics, indicating that the different composting methods influenced subtly the physical and chemical properties of the final products. Overall, the removal selectivity follows the order Pb > Cd > Zn, with the removal percentage ranging from 94.0 to 99.6% for Pb, 55.4-89.8% for Cd and 22.1-64.0% for Zn. Thus, the joint assessment of the characterization and adsorption results shows evidence that composts, a low-cost organic material produced from waste, may be promising as alternative reactive materials for remediation of soils contaminated by Pb, Zn and Cd.
Soil ameliorants can improve soil physico-chemical properties and activate microbial communities in saline-sodic soils. However, there has been less focus on how aggregate fractions affect soil microbial communities under different ameliorant applications. Here, we used the phospholipid fatty acid (PLFA) analysis to explore the effects of soil ameliorants on microbial communities within mega-aggregates (diameter of >2 mm, ME), macro-aggregates (diameter of 0.25–2 mm, MA), and micro-aggregates (diameter of <0.25 mm, MI), based on an 8-year rice (Oryza sativa L.) field experiment. The five treatments included CK, non-amended control; SS, amended with sandy soil; DG, amended with desulfurization gypsum; FM, amended with farm manure; and M, amended with a mixture of sandy soil, desulfurization gypsum, and farm manure. Relative to the CK treatment, the SS, DG, FM, and M treatments significantly decreased the soil pH and electrical conductivity and significantly increased the soil organic carbon (SOC) content of the MI, while the FM and M treatments also significantly improved the SOC content of the MA and ME. Irrespective of the ameliorant used, the absolute abundance of total PLFAs and most microbial groups generally varied with the SOC content as follows: MA > ME > MI. Meanwhile, the proportional abundance of arbuscular mycorrhizal fungi (AMF) varied between different aggregate fractions as follows: ME > MA > MI. Additionally, the DG treatment significantly enhanced the soil aggregate stability by increasing the AMF abundance, AMF/saprotrophic fungi ratio, and SOC content of the MI. Furthermore, soil microbial groups were highly correlated with soil SOC (P < 0.001), C/N ratio (P < 0.001), pH (P < 0.01), total nitrogen (P < 0.01), and the proportion of aggregates with a >0.25 mm diameter (P < 0.05). In conclusion, desulfurization gypsum is more effective for improving the properties of saline-sodic soils in the western Songnen Plain.
Secondary metabolites secreted by microbes and plants act as mediators in plant-microbe interactions including nutrient uptake. However, until now very little is known about their role in nutrient assimilation, particularly amino acids, which are important compounds due to their high N content. Here we show that the addition of flavonoid secondary metabolites, derived from clover, to soil changed the bacterial diversity, enhanced the flux of asparagine, and increased the pools of glutamine/glutamate in the soil. This indicates that flavonoids are functionally important qualitative and quantitative components of clover root exudates. Furthermore, the addition of microbial secondary metabolites negatively affected clover uptake of asparagine and plant performance, which demonstrates that microbial competition for nutrients may have multiple physiological targets in the plant. Finally, the detection of intact asparagine in clover roots confirms that amino acid uptake is significant to the plant in agricultural soil. In conclusion, amino-acid flow in the clover rhizosphere can be modified by the effects of clover-derived flavonoids on the bacterial community structure, which affects the flux and pools of amino acids; microbial secondary metabolites, which reduce clover uptake of asparagine; and direct recapture of amino acids by clover.
The aim of this study was to investigate the dissipation of spirotetramat and its four metabolites (B-enol, B-keto, B-mono and B-glu) in different parts of vegetables belong to the minor crops (Appiacea and Brassicaceae) and soil from cultivation. The challenge of this study was to apply an optimized clean up step in QuEChERS to obtain one universal sorbent for different complex matrices like leaves with high levels of pigments, roots containing acids, sugars, polyphenolls and pigments and soil with organic ingredients. Eight commercial (Florisil, neutral alumina, GCB, PSA, C18, diatomaceous earth, VERDE and ChloroFiltr) and one organic (Chitosan) sorbents were tested. A modified clean up step in QuEChERS methodology was used for analysis. The dissipation of spirotetramat and its metabolites was described according to a first-order (FO) kinetics equation with R(2) between 0.9055 and 0.9838. The results showed that the time after 50% (DT50) of the substance degraded was different for soil, roots and leaves, and amounted to 0.2day, 2.8-2.9days and 2.1-2.4days, respectively. The terminal residues of spiroteramat (expressed as the sum of spirotetramat, B-enol, B-glu, B-keto and B-mono) were much lower than the MRLs.
Soil classification systems are widely used for quickly and easily summarizing soil properties and provide a shorthand method of communication between scientists, engineers, and end-users. Two of the most widely used soil classification systems are the United States Department of Agriculture (USDA) textural soil classification system and the Unified Soil Classification System (USCS). Unfortunately, not all soil map units are classified according to the USDA or USCS systems, and previous attempts to provide a crosswalk table have been inconsistent. Random Forest machine learning model was used to create a USCS prediction model using USDA soil property variables. Important variables for predicting USCS code from available soil properties were USDA soil textures, percent organic material, and available water storage. Prediction error rates less than 2% were achieved compared to error rates of approximately 40% using crosswalk methods.