Soil Microbial Community Abundance Research Articles

Impact mechanisms of various surfactants on the biodegradation of phenanthrene in soil: Bioavailability and microbial community responses

The present study was conducted to systematically explore the mechanisms underlying the impact of various surfactants (CTAB, SDBS, Tween 80 and rhamnolipid) at different doses (10, 100 and 1000 mg/kg) on the biodegradation of a model polycyclic aromatic hydrocarbon (PAH) by indigenous soil microorganisms, focusing on bioavailability and community responses. The cationic surfactant CTAB inhibited the biodegradation of phenanthrene within the whole tested dosage range by decreasing its bioavailability and adversely affecting soil microbial communities. Appropriate doses of SDBS (1000 mg/kg), Tween 80 (100, 1000 mg/kg) and rhamnolipid at all amendment levels promoted the transformation of phenanthrene from the very slow desorption fraction (Fvslow) to bioavailable fractions (rapid and slow desorption fractions, Frapid and Fslow), assessed via Tenax extraction. However, only Tween 80 and rhamnolipid at these doses significantly improved both the rates and extents of phenanthrene biodegradation by 22.1–204.3 and 38.4–76.7 %, respectively, while 1000 mg/kg SDBS had little effect on phenanthrene removal. This was because the inhibitory effects of anionic surfactant SDBS, especially at high doses, on the abundance, diversity and activity of soil microbial communities surpassed the bioavailability enhancement in dominating biodegradation. In contrast, the nonionic surfactant Tween 80 and biosurfactant rhamnolipid enhanced the bioavailability of phenanthrene for degradation and also that to specific degrading bacterial genera, which stimulated their growth and increased the abundance of the related nidA degradation gene. Moreover, they promoted the total microbial/bacterial biomass, community diversity and polyphenol oxidase activity by providing available substrates and nutrients. These findings contribute to the design of suitable surfactant types and dosages for mitigating the environmental risk of PAHs and simultaneously benefiting microbial ecology in soil through bioremediation.

The Application of Orychophragmus violaceus as a Green Manure Relieves Continuous Cropping Obstacles in Peanut Cultivation by Altering the Soil Microbial Community and Functional Gene Abundance

The Application of Orychophragmus violaceus as a Green Manure Relieves Continuous Cropping Obstacles in Peanut Cultivation by Altering the Soil Microbial Community and Functional Gene Abundance

Multi-walled carbon nanotubes affect yield, antioxidant response, and rhizosphere microbial community of scented rice under combined cadmium-lead (Cd–Pb) stress

Rice production is threatened by heavy metal stress. The use of multi-walled carbon nanotubes (MWCNTs) in agriculture has been reported in previous studies. We aimed to quantify the impact of MWCNTs on the growth and physiological characteristics of scented rice under cadmium (Cd) and lead (Pb) stresses. Therefore, a pot experiment was conducted, two scented rice varieties Yuxiangyouzhan and Xiangyaxiangzhan were used as materials grown under different concentrations of MWCNTs (0, 100, and 300 mg kg−1 recorded as CK, CNPs100, and CNPs300, respectively). The yield, antioxidant response, and rhizosphere microbial community of scented rice were studied. The results showed that compared with the CK treatment, the CNPs100 and CNPs300 treatments increased leaf dry weight by 17.95%–56.22% at the heading stage, and the H2O2 content in leaves decreased significantly by 36.64%–42.27% at the maturity stage. Under CNPs100 treatment, the grain yield of two scented rice varieties increased significantly by 17.54% and 27.40%, respectively. The MWCNTs regulated the distribution of the Cd and Pb in different plant tissues. The content of Cd (0.11–0.20 mg kg−1) and Pb (0.01–0.04 mg kg−1) in grain were at a safety level (<0.2 mg kg−1). Moreover, MWCNTs increased soil microbial community abundance and altered community composition structure under Cd–Pb stress, which in turn improved agronomic traits and quality of scented rice. Overall, this study suggested that the application of MWCNTs regulates the growth, yield, physiological response, and soil microbial community, the genotypes response effect of scented rice to MWCNTs is needed further studied.

Prairie restoration promotes the abundance and diversity of mutualistic arbuscular mycorrhizal fungi.

Predicting how biological communities assemble in restored ecosystems can assist in conservation efforts, but most research has focused on plants, with relatively little attention paid to soil microbial organisms that plants interact with. Arbuscular mycorrhizal (AM) fungi are an ecologically significant functional group of soil microbes that form mutualistic symbioses with plants and could therefore respond positively to plant community restoration. To evaluate the effects of plant community restoration on AM fungi, we compared AM fungal abundance, species richness, and community composition of five annually cultivated, conventionally managed agricultural fields with paired adjacent retired agricultural fields that had undergone prairie restoration 5-9 years prior to sampling. We hypothesized that restoration stimulates AM fungal abundance and species richness, particularly for disturbance-sensitive taxa, and that gains of new taxa would not displace AM fungal species present prior to restoration due to legacy effects. AM fungal abundance was quantified by measuring soil spore density and root colonization. AM fungal species richness and community composition were determined in soils and plant roots using DNA high-throughput sequencing. Soil spore density was 2.3 times higher in restored prairies compared to agricultural fields, but AM fungal root colonization did not differ between land use types. AM fungal species richness was 2.7 and 1.4 times higher in restored prairies versus agricultural fields for soil and roots, respectively. The abundance of Glomeraceae, a disturbance-tolerant family, decreased by 25% from agricultural to restored prairie soils but did not differ in plant roots. The abundance of Claroideoglomeraceae and Diversisporaceae, both disturbance-sensitive families, was 4.6 and 3.2 times higher in restored prairie versus agricultural soils, respectively. Species turnover was higher than expected relative to a null model, indicating that AM fungal species were gained by replacement. Our findings demonstrate that restoration can promote a relatively rapid increase in the abundance and diversity of soil microbial communities that had been degraded by decades of intensive land use, and community compositional change can be predicted by the disturbance tolerance of soil microbial taxonomic and functional groups.

Effects of reduced snowpack due to climate warming on abiotic and biotic soil properties in alpine and boreal forest systems

Reduction in snow cover, depth, onset, and duration of seasonal snow in mid-latitude regions due to climate warming has multiple global and local scale ecosystem impacts. These effects include modulations of the hydrological cycles and increases in land surface solar radiation absorption due to decreased albedo. Changes in snow cover characteristics also affect underlying soils. Snow has an insulating effect on soils by decoupling air and soil temperatures, thus seasonal snow cover reduction leads to overall lower soil temperatures and an increase in freeze-thaw cycles. This is especially prominent during the fall and spring thaw seasons when the snow cover is not as extensive. This in turn has downstream impacts on soil physical, chemical, and biological properties. Among these impacts are soil moisture reduction, temperature, frost regimes, soil pH shifts, and alteration in nutrient flux dynamics during winter, snowmelt period and the following summer growing season. These changes in soil physicochemical properties due to snowpack reduction can then impact the biological soil properties via increased plant root mortality, reduced abundance and diversity of soil arthropods, and shifts in composition, abundance and activity of soil microbial communities. All these soil biotic factors can in turn alter the dynamics of soil nutrient fluxes and future greenhouse gas emissions. Here, we integrate data on the effects of snow cover reduction on abiotic and biotic soil properties, with focus on temperate alpine and forest ecosystems and with an outlook on future impacts.

Effects of molasses-based microbial dust suppressant on soil dust and microbial community

This study aims at the practical needs of soil dust control and molasses resource utilization. By adding molasses to the soil and combining it with the components of microbial dust suppressants, it explores its impact on the surface soil dust suppression performance and microbial communities. The results show that after spraying treatment, the soil surface hardness is positively correlated with the molasses concentration, the surface hardness is the highest (41.14 HA) when the molasses concentration is 10%; the anti-wind erosion effect shows a trend of first increasing and then decreasing with the molasses concentration, the anti-rain erosion effect needs to be improved; microbial community analysis show that molasses significantly affected the relative abundance of soil microbial community, and appropriate addition (1%) could optimize the microbial community structure and enhance the functions of carbohydrate and energy metabolism pathways, and the abundance of pathogenic species increased when the molasses concentration was higher (above 5%). Therefore, considering the dust suppression effect and environmental safety, a dust suppressant with a molasses concentration of 1% is more suitable for dust suppression. However, the synergistic pathway and mechanism of dust suppression through the interaction between molasses and MICP technology need to be further explored.

Effects of Microtopography on Soil Microbial Community Structure and Abundance in Permafrost Peatlands.

Soil microorganisms play crucial roles in the stability of the global carbon pool, particularly in permafrost peatlands that are highly sensitive to climate change. Microtopography is a unique characteristic of peatland ecosystems, but how microtopography affects the microbial community structures and their functions in the soil is only partially known. We characterized the bacterial and fungal community compositions by amplicon sequencing and their abundances via quantitative PCR at different soil depths in three microtopographical positions (hummocks, flats, and hollows) in permafrost peatland of the Greater Xing'an Mountains in China. The results showed that the soil of hummocks displayed a higher microbial diversity compared to hollows. Microtopography exerted a strong influence on bacterial community structure, while both microtopography and soil depth greatly impacted the fungal community structure with variable effects on fungal functional guilds. Soil water content, dissolved organic carbon, total phosphorus, and total nitrogen levels of the soil mostly affected the bacterial and fungal communities. Microtopography generated variations in the soil water content, which was the main driver of the spatial distribution of microbial abundances. This information stressed that the hummock-flat-hollow microtopography of permafrost peatlands creates heterogeneity in soil physicochemical properties and hydrological conditions, thereby influencing soil microbial communities at a microhabitat scale. Our results imply that changes to the water table induced by climate warming inducing permafrost degradation will impact the composition of soil microbes in peatlands and their related biogeochemical functions, eventually providing feedback loops into the global climate system.

Effects of Different Conditioners on Soil Microbial Community and Labile Organic Carbon Fractions under the Combined Application of Swine Manure and Straw in Black Soil

The return of straw and manure to agricultural fields can impact soil organic carbon (SOC) and biological properties. However, there is a lack of research on how using swine manure, maize straw, and various conditioners together affects soil bacterial and fungal populations. This study aimed to investigate six treatments, namely, only maize straw (S00), maize straw combined with swine manure (S0Z), maize straw combined with biochar and swine manure (SCZ), maize straw combined with boron slag and swine manure (SBZ), maize straw combined with biological agent and swine manure (SJZ), and maize straw combined with bio-organic fertilizer and swine manure (SFZ). The results showed that after the two-year return, all treatments increased the SOC content in 2023, which was 12.55–26.89% higher than S00, and the SCZ treatment significantly increased the soil organic carbon (SOC), dissolved organic carbon (DOC), easily oxidizable carbon (EOC), particulate organic carbon (POC), and microbial biomass carbon (MBC) content by 26.89%, 25.44%, 56.88%, 16.08%, and 43.54%, compared to S00. A redundancy analysis (RDA) showed that the continuous application of manure, maize straw, and conditioners has a positive impact on the diversity and abundance of soil microbial communities, enhancing the accumulation of soil carbon. Furthermore, our research revealed that soil fungi exhibited higher sensitivity in soil carbon composition following the addition of manure, straw, and conditioners to agricultural fields than bacteria. In conclusion, the addition of different conditioners to the fields is beneficial to biodiversity conservation from the perspective of achieving soil carbon storage and soil protection. Our findings suggested that the combination of maize straw, biochar, and swine manure has been proven to be the most effective treatment for increasing labile organic carbon fractions and enhancing the microbial community.

Response mechanism of soil microorganisms to simulated precipitation in the source wetland of Qinghai Lake

BackgroundChanges in precipitation patterns crucially impact soil microbial communities, and the ecosystem in Qinghai-Tibet Plateau (QTP) is highly vulnerable to climate change. However, we do not fully understand how soil microbial communities in the source wetlands of QTP respond to changes in precipitation. In this study, we employed advanced techniques such as high-throughput sequencing and metabolomics to investigate how soil microbial communities in a source wetland of Qinghai Lake respond to changes in precipitation after quadrennial precipitation treatment.ResultsOur findings showed that the predominant microbiota in the source wetland was Proteobacteria. Interestingly, alterations in precipitation levels, whether increased or reduced, did not significantly impact the diversity or functional groups of the microbial community. However, the structure of the microbial community did respond notably to changes in precipitation, leading to shifts in the relative abundance of Spirochaetes and Treponema. A notable finding was that reduced precipitation levels (– 25% and − 50%) and mild increases in precipitation (25%) within the region contributed to increased soil carbon content. However, this effect ceased to manifest when precipitation increased by 50%. Additionally, the reduction in precipitation prompted the release of soil metabolites like syringic acid and aldosterone, while enhanced precipitation resulted in a decrease in aldosterone content.ConclusionsPrecipitation changes altered the relative abundance of soil microbial communities and metabolites, which was conducive to increasing carbon storage in this alpine wetland.

Remediation of cadmium-contaminated soil by biochar-loaded nano-zero-valent iron and its microbial community responses

At present, cadmium (Cd)-contaminated soil has been increasingly serious, which is adverse to soil health. In this study, biochar (BC) and biochar-loaded nanoscale zero-valent iron (nZVI@BC) were synthesized for remediation of Cd-contaminated soil. The effects of various factors including reaction time, dosage, nZVI loading on Cd fractionation, soil available iron, pH, CEC, and soil enzyme activity were comprehensively discussed. It can be concluded that nZVI@BC exhibited more excellent immobilization effect of Cd, and was positively correlated with dosage and reaction time, but negatively related to nZVI loading. As a result, 5% nZVI@BC(1:3) performed the best. Soil available iron, pH, and CEC were significantly enhanced with increasing nZVI loading. The immobilization mechanism was analyzed, including ion exchange, physical adsorption, surface complexation, electrostatic attraction as well as co-precipitation. Besides, nZVI@BC remarkably promoted soil catalase activity, but inhibited urease and FDA hydrolase activities. Furthermore, the effects and differences on the diversity, abundance, and species composition of soil microbial communities were deeply explored. The order of bacterial community richness in each group was CK > Cd > BC > nZVI@BC, and the bacterial community diversity was CK > nZVI@BC > Cd > BC. The greatest difference of species abundance composition was observed between nZVI@BC treatment group and the control. Additionally, forty-three biomarkers were screened, which primarily belonged to Proteobacteria, Gemmatimonadetes, Firmicutes, and Actinobacteria. This study will provide the profound theoretical basis for nZVI@BC remediation of Cd-contaminated soil and its microbial community responses.

Selenium Fertilizer Improves Microbial Community Structure and Diversity of Rhizospheric Soil and Selenium Accumulation in Tomato Plants

ABSTRACT Selenium (Se) is an essential microelement in living organisms, and has a beneficial effect on plant growth and stress tolerance at low concentrations. Se biofortification is commonly practiced in agriculture and is considered the best method for increasing human Se uptake. This study aimed to investigate the effects of Se fertilizer application on Se accumulation and microbial communities in the rhizospheric soil of tomato plants. A pot experiment with five treatments, i.e. (a) non-Se fertilizer as control (Ck) and Se fertilizer in the form of (b) sodium selenite (1 mg kg−1), (c) sodium selenite (5 mg kg−1), (d) sodium selenate (1 mg kg−1), and (e) sodium selenate (5 mg kg−1) was set up. The results showed that Se content in the tomato plants’ parts gradually increased with an increasing concentration of sodium selenate or selenite. Sodium selenate significantly increased tomato yield and improved Se accumulation in tomato plants. Se-treated treatments decreased the abundance of soil microbial community, and had no effect on the Chao1 and Shannon indices of them. Furthermore, Se application increased the relative abundance of Acidobacteriota and Actinobacteriota involved in the decomposition of organic matter, reducing Bacteriodota and Ascomyta, and significantly affected the bacterial community structure. Thus, Se fertilizer application increased the crop yield, improved Se accumulation, and the structure and diversity of rhizospheric soil microbial community in the tomato plants. In line with our experiment, 5 mg kg−1 concentration selenate is a reasonable way to harvest Se-enriched tomatoes.

Mitigation of aeolian erosion of loess soil by Bio-Stimulated microbial induced calcite precipitation

Microbial-induced calcite precipitation (MICP) is a soil amelioration technique that addresses various environmental and engineering concerns. Here, we present a study focusing on aeolian erosion control of loess soil from the Negev Desert (Israel). Changes in the treated soil's chemical, physical, and microbial community (abundance and diversity) were characterized following bio-stimulation of native, urea-hydrolyzing soil bacteria to achieve MICP. Bio-stimulation of the loess soil was induced in liquid media (batch experiments) and by spraying soil trays with stimulation media (urea and yeast extract). These experiments showed that the Negev loess could be readily stimulated to induce bacterial urea hydrolysis. Three to four daily sprayings were sufficient to achieve effective bio-stimulation, evidenced by a high hydrolysis rate and an alkaline pH. Erodibility experiments on a decimeter scale (50 cm x 50 cm trays) were performed on loess sprayed with treatment media with varying concentrations of urea and CaCl2, with a constant 1:1 M ratio. The effectiveness of the treatments was studied in a wind tunnel and by image analysis of desiccation cracks. Upscaling of the experiments to the large trays revealed a more complicated reality with urease activity, community composition, and calcium carbonate precipitation depending on the concentration of the treatment medium. Specifically, we show that a twofold reduction in the area and length of the desiccation cracks can be achieved by spraying the soil with a 0.5 M solution, resulting in effective MICP or a high concentration treatment (>1M solution) without achieving MICP. Our results show that erosion mitigation in loess soil depends on an interplay between biotic and abiotic processes based on the treatment media concentration and provides a necessary step for upscaling the bio-stimulated MICP strategy for future field implementations.

Assessing the aging and environmental implications of polyethylene mulch films in agricultural land.

Polyethylene mulch films (MFs) are widely employed in agricultural land to enhance crop yield and quality, but the MF residue causes significant environmental concerns. To promote the sustainable application of MFs, it is essential to assess their fate throughout their service life and understand the underlying degradation mechanisms. In this study, surface-exposed and soil-buried MFs were separately collected from agricultural land in Inner Mongolia, China. The variations in aging performance and corresponding property alterations of MF were thoroughly examined. The results indicated that sunlight exposure considerably hastens MF degradation, whereas buried MFs experience a more moderate aging process due to the inhibitory effects of the dark and anaerobic environment on oxidation. Surface cracking was observed in MF-Light samples as a result of photodegradation, while chemical and moisture interactions with soil caused partial perforation in MF-Soil samples. Relative to the pristine MF, the oxidation, unsaturation, and hydroxylation levels of MF-Light increased to 0.88, 0.35, and 0.73, respectively, with corresponding values for MF-Soil at 0.44, 0.13, and 0.24. The generated oxygen-containing functional groups lead to a decrease in contact angles of MF-Light and MF-Soil, enhancing their hydrophilicity. The aging process of MFs led to a decline in mechanical properties, posing challenges for recycling. Moreover, nearly all phthalate esters (PAEs) were released from MFs, regardless of sunlight exposure or soil burial. The use of MFs also impacted the abundance of soil microbial communities. Specifically, the selected polyethylene MF enriched Actinobacteriota by 75%, while reducing Chloroflexi and Firmicutes by 27% and 45%, respectively.

Effect of micro–nano bubbles on the remediation of saline–alkali soil with microbial agent

The widespread distribution of saline–alkali soil around the world affects the health of ecological systems and the development of the national economy by limiting the growth of plants. However, the commonly used remediation technologies have the drawbacks of low efficiency, high cost, and secondary pollution. This study investigated the feasibility and efficacy of novel combined micro–nanobubbles (MNBs) and microbial agent (MA) technology for the remediation of saline–alkali soil. The results demonstrated that the combined MA–MNBs method greatly renovated the properties of saline–alkali soil compared with the technologies of single utilization of MA or MNBs process in the laboratory. The method resulted in a reduction of soil electrical conductivity and pH levels, an improvement in soil fertility, and the formation of soil aggregates. Moreover, the method significantly impacted the growth of plants, particularly in plant length, dry weight, and rhizome elongation. Further high–throughput sequencing and gene expression analysis revealed that the MA–MNBs method enhanced the abundance of soil microbial community compared with single MA and MNBs treatment. Gene enrichment analysis revealed that the MA–MNBs method could compensate for the shortcomings of single MA treatment and enhance the expression of energy metabolism and salt stress–related genes attributed to MNBs treatment, thereby significantly improving the growth and development of plants. Consistently, 6115 kg/ha of rice was yielded in the field for the saline–alkali soils using this MA–MNBs method, with zero crops before remediation. This study provided a novel, efficient, and green strategy for the remediation of saline–alkali soil without adding any chemicals.

Effects of Continuous Manure Application on the Microbial Community and Labile Organic Carbon Fractions

The application of organic materials contributes to the sustainable development of agriculture. Increased manure inputs have a fundamental effect on the composition and dynamics of soil organic carbon (SOC). In this study, we conducted a 10-year field experiment in Changchun, Jilin, Northeast China, to investigate the effects of manure addition on soil organic carbon components and soil microorganisms. Specifically, we established four treatments: (i) chemical fertilizer or no addition of manure (CK), (ii) pig manure with chemical fertilizer (ZF), (iii) cow manure with chemical fertilizer (NF), and (iv) chicken manure with chemical fertilizer (JF). The results showed that the JF treatment significantly increased the soil organic carbon (SOC), dissolved organic carbon (DOC), and readily oxidized organic carbon (ROC) content by 20.36%, 105.9%, and 61.32%, respectively, relative to CK. The microbial biomass carbon (MBC) content in JF, ZF, and NF treatments were significantly higher than that of CK, which increased by 107.24%, 116.45%, and 96.71%, respectively. The particulate organic carbon (POC) content in NF and JF treatments differed significantly, increasing by 25.61% and 19.01%, respectively, relative to CK. Redundancy analysis showed that continuous manure application had a positive effect on soil microbial community diversity and abundance, which was favorable for the accumulation of soil carbon. We also found that soil fungi were more sensitive than bacteria to changes in soil carbon composition following manure application. In conclusion, adding different organic materials can better support biodiversity conservation and realize ecosystem services of surface carbon storage and soil conservation. Our results reveal the importance of microbial fixation in soil carbon dynamics according to the different distribution of active organic carbon pools, which will help enhance our understanding of the carbon cycle.

Differences in Rhizosphere Microbial Community Structure and Composition in Resistance and Susceptible Wheat to Fusarium Head Blight

Fusarium head blight (FHB) is a serious disease of wheat that threatens wheat production worldwide. In this study, high-throughput sequencing technology was used to analyze the rhizosphere soil microbial metagenomes of 4 wheat cultivars with different levels of resistance to FHB. The results showed that there were differences in the diversity, structure, and composition of rhizosphere microorganisms between resistant and sensitive varieties. The rhizosphere soil bacterial diversity of the resistant wheat varieties Su Mai 3 and Yang Mai 16 was higher than that of the susceptible wheat varieties Zheng Mai 9023 and Zhou Mai 20. The diversity of rhizosphere fungi in resistant varieties was lower than that in susceptible varieties, but the abundance was higher than that in susceptible varieties. Variety was found to alter the community structure of wheat rhizosphere microorganisms. Resistant varieties SM3 and YM16 and moderately susceptible variety ZM9023 had similar microbial community structure, while highly susceptible variety ZM20 was significantly different from other varieties. The study is aimed at analyzing the effects of wheat varieties of different resistance to FHB on the composition and abundance of rhizosphere soil microbial community to screen out bacteria or fungi that can be used to control FHB, providing the theoretical basis for FHB biological control.

Accelerated spent coffee grounds humification by heat/base co-activated persulfate and products’ fertilization evaluation

Coffee, as the second most common beverage in the world, produced 60% of spent coffee grounds (SCG) with per ton of coffee beans processed. SCG is a typical lignocellulosic-rich organic waste and mainly disposed via composting or incineration. In this study, a rapid humification approach was proposed for the recycling of SCG using heat/base co-activated persulfate (heat/KOH/PS) advanced oxidation process. The yields of humic-like acid (HLA) and fulvic-like acid (FLA) reached 45 (3.96%) and 192 mg/g (19.2%) under the optimal humification conditions of 1% PS and 4% KOH at 100 ℃ in 1 h. The typical active groups of -OH and -COOH in FA standard were observed with higher amounts in the product compared to SCG, which may be related to occurrence of hydroxylation, carboxylation and Maillard reactions during humification. Radicals of •OH and SO4•- were identified in heat/KOH/PS system and made significant contribution to SCG humification. A slow-release nano FLA fertilizer (SNFF) was prepared by mixing treated SCG with attapulgite and showed good slow-release behaviors of HLA and FLA. In pot experiments with acid soil, SNFF increased the average root length of chickweeds by 233% compared with blank. Meanwhile, SNFF also contributed to increased abundance and richness of soil microbial community as well as a pH rise from 5 to 6.7, which was conducive to acid soil amendment. The earthworm test indicated positive ecological safety of SNFF. Overall, this study highlights an efficient humification method for the recycling of organic biowaste such as SCG in green agriculture.

Comparison of Soil Microbial Community between Managed and Natural Vegetation Restoration along a Climatic Gradient in Karst Regions

Managed and natural vegetation restorations are two vital measures of land restoration; however, their effects on soil microbial communities at a large scale are not clearly understood. Hence, changes in the microbial community composition after 15 years of vegetation restoration along a climatic gradient in the subtropical karst region of Southwest China were assessed based on phospholipid fatty acids (PLFAs) profiles. Managed (plantation forest) and natural (naturally recovered to shrubbery) vegetation restoration types were compared, with cropland and mature forest serving as controls. Soil microbial community abundance was significantly higher under the two vegetation restoration types than in the cropland; however, it was lower than in the mature forest. The abundance, composition, and structure of soil microbial communities did not differ significantly between plantation forest and shrubbery. Soil organic carbon or total nitrogen was the primary factor positively affecting soil microbial abundance, whereas the mean annual temperature (MAT) was recognized as the primary factor contributing to the variation in the soil microbial community structure. Moreover, temperature had opposite effects on different indicators of microbial community structure. That is, it positively and negatively affected the ratios of gram-positive to gram-negative bacterial PLFAs (GP:GN) and fungal to bacterial PLFAs (F:B), respectively. Our results show that both vegetation restoration types have the ability to improve soil productivity in karst areas. Furthermore, shifts in soil microbial community structure (GP:GN and F:B ratios) induced by warming are likely to lead to a higher proportion of labile carbon, which is sensitive to soil tillage. Hence, more attention should be paid to ecological restoration in warmer karst areas to alleviate the severe loss of soil carbon in croplands.

Elevated CO2, O3 and their interaction have differential impact on soil microbial diversity and functions in wheat agroecosystems

Elevated carbon dioxide (EC) and elevated ozone (EO) due to changing climate have a significant impact on the plant growth rate, primary productivity, and root turnover. EC and EO could have a differential impact on the structure and functioning of soil microbial communities in terrestrial ecosystems via modifications in the microbial population, soil enzyme activity, decomposition of organic compounds and cycling of nutrients. For the development of sustainable agroecosystems, soil microbial communities are essential due to their major roles in nutrient cycling, crop-microbe interplay and resistance towards biotic/abiotic factors. However, it remains difficult to project how multiple climate change factors would affect below-ground functions. Free-Air CO2 and O3 enrichment facility (FAOCE) was used to explore the effects of EC (550 ± 50 ppm) and EO (65 ± 10 ppb) along with their combined interactive treatment ECO on the structure and abundance of soil microbial community, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) and microbes involved in N cycling in wheat crop (Triticum aestivum) under field conditions. The MBC increased by 20% in EC and declined by 5% in EO to ambient control. Treatments EC and ECO stimulated the growth of ammonia and nitrite-oxidizing bacteria. Heterotrophic microbial populations were favoured under EC and inhibited under EO. Treatments indirectly affected the soil microbial community structure by altering N-cycling microbes and modifying MBC and MBN which eventually changed soil fertility and biogeochemistry.

Impacts of Land Use Intensification Level on Fluvo-aquic Cropland Soil Microbial Community Abundance and Necromass Accumulation in North China

Despite the essential role of soil microorganisms in nutrient turnover in soil ecological systems and the recognized paramount significance of microbial necromass to soil organic carbon accumulation, how microbial community abundance and necromass respond to land use intensification level regulation remains poorly understood. To address this knowledge gap, based on the land use intensification level, three treatments were set up[annual wheat-maize rotation (CC), alternating temporary grassland with wheat planting (TG), and perennial grassland (PG)], and a long-term fixed filed experiment was established to investigate the influences of the regulation of land use intensification level on bacterial and fungal community abundances; the accumulation of bacterial, fungal, and total microbial necromass; and their contributions to SOC sequestration using droplet digital PCR and amino sugar detection technologies. We further sought to determine the key factors driving the bacterial, fungal, and total microbial necromass C accumulation. Our results demonstrated that fungal community abundance was strongly affected by land use intensification level regulation compared to that of the bacterial community, which increased with decreasing land use intensification level. The total microbial necromass C predominated the SOC accumulation across all three land use intensification levels, which contributed 52.78%, 58.36%, and 68.87% to SOC, respectively, exhibiting an increasing trend with the decline in land use intensification level. Fungal necromass C accounted for more than 80% of the total microbial necromass C, indicating its predominance in the accumulation of the total microbial necromass C and active variation via the reduction in land use intensification level. There was no significant difference in bacterial necromass C (MurA) content, with the trend of CC<PG<TG, whereas fungal necromass C (GluN) was observed to be significantly shifted by the modulation of land use intensification level, with contents in the TG and PG treatments being higher than that in the CC treatment, especially for the PG treatment (with an increase of 66.10%). The increase in bacterial necromass C accumulation was associated with microbial demand for N and was affected by the balance between soil C and N; however, the accumulation of fungal necromass C was jointly manipulated by a wide variety of biotic and abiotic factors. Altogether, our work provides evidence that agricultural land use intensification level regulation can enhance soil extracellular enzyme activity and accelerate nutrient transformation through changing edaphic properties, thus improving fungal amount and necromass C accumulation, with active contribution to total microbial necromass C and even SOC.