Soil Microbial Characteristics Research Articles

Effects of Film Mulching on Soil Microbial Diversity and Community Structure in the Maize Root Zone under Drip Irrigation in Northwest China

Mulching is a widely used agricultural water conservation measure in the semiarid regions of Northwest China. In order to explore the response process of different film mulching methods to soil microorganisms, we characterized the effect of different film mulching methods on soil microbial diversity and community structure characteristics in the root zone of drip-irrigated maize during the heading and maturity stages using high-throughput sequencing of 16SrDNA and ITS amplicons combined with bioinformatics analysis. Full mulching (FM) was contrasted to controls of no mulching (NM) and half-mulching (HM), yielding an order of microbial diversity, abundance, and evenness scores of HM > FM > NM. The HM and FM treatments reduced the relative abundance of Proteobacteria and Actinobacteria (the most abundant bacteria) in the bacterial community structure but increased that of Acidobacteria and Chloroflexi. In the fungal community structure, HM decreased the abundance of Sordariomycetes but increased that of Eurotiomycetes (the most abundant fungi). The abundance and community structure of bacteria were significantly correlated with soil temperature and those of fungi with pH. HM improved network complexity and competitive relationships among bacteria, while FM increased the relationship between fungal groups and the symbiosis of fungal communities. HM significantly increased maize yield (20.37% and 6.01% above NM and FM, respectively). In summary, full mulching was more favorable than no mulching for soil microbial diversity and community structure composition, but soil microbial diversity and yield responded better to half-mulching. These results provide a background for improving the yield of drip-irrigated maize and protecting the microbial ecosystems of farmland soils.

Nitrogen application increases the productivity of perennial alpine cultivated grassland by improving soil physicochemical properties and microbial community characteristics

Nitrogen application increases the productivity of perennial alpine cultivated grassland by improving soil physicochemical properties and microbial community characteristics

Microplastic coupled with soil dissolved organic matter mediated changes in the soil chemical and microbial characteristics

The abundance of microplastics (MPs) in soil environments has attracted significant attentions, due to their impact on soil physico-chemical properties. However, limited information is available on the influences of MPs on soil carbon composition and microbial utilization characteristics. Therefore, a two-month incubation experiment was conducted to add polyethylene microplastics (PE-MPs) with different levels (1%, 10%) and sizes (150–300 μm and 75–150 μm) into different soils. After that, soil chemical properties including the dissolved organic carbon (DOC), spectral characteristics of dissolved organic matter (DOM) and soil microbial characteristics were analyzed. Results revealed that PE-MPs addition caused significant differences in soil chemical properties between farmland and woodland soils, particularly in soil pH, DOM composition, and soil phosphatase activity. Woodland soil always exhibited higher levels of DOC content, microbial diversity, and soil carbon source utilization compared to farmland soil, leading to increased humification in the DOM of woodland soil. PE-MPs with a larger particle size significantly increased both the soil DOC content and enzyme activity. Addition of PE-MPs altered the soil DOM composition, and the fluorescence parameters like the biological index (BIX) and humification degree. Moreover, the carbon source utilization intensity of microorganisms on PE MPs-contaminated soils is higher in woodland soils. Various analyses confirmed that compared to other soil properties, characteristics of soil DOM had a more significant impact on soil microbial community composition. Thus, PE-MPs in conjunction with soil DOM spectral characteristics regulated soil microbial diversity, which is crucial for understanding soil carbon sequestration.

Soil Microbial Community Characteristics and Their Effect on Tea Quality under Different Fertilization Treatments in Two Tea Plantations.

Fertilization is an essential aspect of tea plantation management that supports a sustainable tea production and drastically influences soil microbial communities. However, few research studies have focused on the differences of microbial communities and the variation in tea quality in response to different fertilization treatments. In this work, the soil fertility, tea quality, and soil microbial communities were investigated in two domestic tea plantations following the application of chemical and organic fertilizers. We determined the content of mineral elements in the soil, including nitrogen, phosphorus, and potassium, and found that the supplementation of chemical fertilizer directly increased the content of mineral elements. However, the application of organic fertilizer significantly improved the accumulation of tea polyphenols and reduced the content of caffeine. Furthermore, amplicon sequencing results showed that the different ways of applying fertilizer have limited effect on the alpha diversity of the microbial community in the soil while the beta diversity was remarkably influenced. This work also suggests that the bacterial community structure and abundance were also relatively constant while the fungal community structure and abundance were dramatically influenced; for example, Chaetomiaceae at the family level, Hypocreaceae at the order level, Trichoderma at the genus level, and Fusarium oxysporum at the species level were predominantly enriched in the tea plantation applying organic fertilizer. Moreover, the bacterial and fungal biomarkers were also analyzed and it was found that Proteobacteria and Gammaproteobacteria (bacteria) and Tremellomycetes (fungi) were potentially characterized as biomarkers in the plantation under organic fertilization. These results provide a valuable basis for the application of organic fertilizer to improve the soil of tea plantations in the future.

Appropriate Application of Organic Fertilizer Can Effectively Improve Soil Environment and Increase Maize Yield in Loess Plateau

Fertilization has a significant impact on soil nutrients and microbiological properties, which, in turn, affect crop yield. However, the specific effects of organic and inorganic fertilizers on soil fertility and microbial characteristics in maize fields, as well as the key soil factors influencing changes in crop yield, remain largely unknown. A study was conducted over two years (2021–2022) to investigate the impact of various nitrogen fertilization rates and types on maize yield and soil properties in the Loess Plateau. Field experiments with five nitrogen levels (60, 90, 120, 150, and 180 kg N ha−1) and two fertilizer types (chemical and organic) were conducted. The optimal yield was achieved with 150 kg N ha−1, significantly surpassing that of other treatments by 4.5−45.7%. Compared with the organic fertilizers, the chemical fertilizers increased soil salt and catalase levels, with soil nitrate and ammonium content being higher at the jointing stage but lower at maturity. Organic fertilization improved soil potassium, organic matter, urease and phosphatase activities, and microbial populations. Yield correlated with several soil indicators, including salt content, nitrate, available potassium, and enzyme activities. Notably, soil nitrate also correlated with actinomyces quantity. A principal component analysis showed that the organic fertilizer was more beneficial to soil health than the chemical fertilizer. Consequently, this study recommends 150 kg N ha−1 of organic fertilizer for sustainable maize farming and soil health in China’s northwest arid region, providing a theoretical framework for agricultural practices.

Mixing of pine and arbuscular mycorrhizal tree species changed soil organic carbon storage by affecting soil microbial characteristics

Pure and mixed pine forests are found all over the world. The mycorrhizal type affects soil microbial activity and carbon sequestration capacity in pure forests. However, the effects of mycorrhizal type on microbial characteristics and carbon sequestration capacity in pine mixed forests remain untested. Further, making it difficult to predict carbon storage of the conversion from pure pine forests to mixed forests at larger scales. Herein, a meta-analysis showed that the contents of soil microbial biomass, mineral-associated organic carbon, and soil organic carbon in pine mixed forests with introduced arbuscular mycorrhizal tree species (PMAM) increased by 26.41 %, 58.55 %, and 27.41 %, respectively, compared to pure pine forests, whereas those of pine mixed forests without arbuscular mycorrhizal tree species (PMEcM) remained unchanged. Furthermore, the effect size of microbial biomass, mineral-associated organic carbon and organic carbon contents in subsoil of PMAM are 56.48 %, 78.49 % and 43.05 %, respectively, which are higher than those in topsoil. The improvement of carbon sinks throughout the PMAM soil profile is positively correlated with increases in microbial biomass and mineral-associated organic carbon in subsoil, according to regression analysis and structural equation modelling. In summary, these results highlight that the positive effects of introducing arbuscular mycorrhizal tree species rather than ectomycorrhizal tree species into pure pine forests on soil microbial biomass and carbon sequestration. The positive link between microbial biomass, mineral-associated organic carbon, and soil organic carbon suggests an underlying mechanism for how soil microorganisms store carbon in pine mixed forests. Nevertheless, our findings also imply that the soil carbon pool of PMAM may be vulnerable under climate change. Based on the above findings, we propose that incorporating mycorrhizal type of tree species and soil thickness into mixed forests management and biodiversity conservation.

Soil Nutrient, Enzyme Activity, and Microbial Community Characteristics of E. urophylla × E. grandis Plantations in a Chronosequence

The effects of continuous Eucalyptus cropping on soil properties and microbial characteristics and the specific factors influencing tree species growth remain elusive. In this study, three Eucalyptus stands of three different ages were selected, and soil nutrients, microbial biomass, enzyme activity, microbial community composition, and diversity were quantified for each. The findings indicated a significant decline in soil pH, soil cation exchange, soil organic matter, and available phosphorus content with the plantation age. Simultaneously, there was an observed increase in soil alkaline hydrolyzed nitrogen content. In addition, urease and acid phosphatase activities did not show a significant difference with age. In spite of this, catalase activity exhibited a decline corresponding to the advancement in plantation age. The carbon and nitrogen content of the soil microbial biomass increased with the progression of Eucalyptus planting time. The high-throughput sequencing data demonstrated a reduction in microbial diversity in Eucalyptus soils as the planting age increased. Interestingly, the microbial community structure exhibited minimal alterations, and did not exhibit a predominantly oligotrophic state overall. In conclusion, the study results showed that short-term successive Eucalyptus cropping exerts a significant negative impact on the soil system.

Vertical differentiation drives the changes in the main microflora and metabolites of carbon and nitrogen cycling in the early freeze-thaw period in the Qinghai Lake Basin.

Global climate change has altered the frequency of soil freeze-thaw cycles, but the response of soil microorganisms to different elevation gradients during the early freeze-thaw period remains unclear. So far, the influence of the altitudinal gradient on the microbial community and metabolic characteristics in the early freeze-thaw period of the Qinghai Lake Basin remains unclear. To this end, we collected soil at different elevations in the early freeze-thaw period of the Qinghai Lake Basin and investigated the influence of the elevation gradient on soil microbial community characteristics and soil metabolic processes as well as the corresponding environmental driving mechanism by high-throughput sequencing and LC-MS (Liquid Chromatograph-Mass Spectrometer) nontargeted metabolite determination. The results showed that Proteobacteria were the dominant microflora in the Qinghai Lake Basin. The dominant phyla associated with carbon and nitrogen are Proteobacteria and Firmicutes, both of which are significantly affected by elevation. The soil physicochemical factors jointly affected the soil microbial communities and metabolism. Total phosphorus nitrate nitrogen and pH were the main driving factors of the microbial community, and metabolites were sensitive to changes in chemical factors. In short, the microbial community structure and function, soil physicochemical factors and soil metabolic processes were significantly affected by the altitudinal gradient in the early freeze-thaw period, while the microbial community diversity showed no significant response to the altitudinal gradient. Additionally, a high potassium content in the soil may promote the growth and reproduction of bacteria associated with carbon and nitrogen cycling, as well as the production of metabolites.

Optimizing organic fertilization towards sustainable vegetable production evaluated by long-term field measurement and multi-level fuzzy comprehensive model

Precision and efficient management of organic substitution fertilization is crucial in balancing soil health, environmental risks, and economic benefits for intensive crop cultivation. However, effectively determining the optimal organic substitution ratio in vegetable production remains uncertain and still relatively unexplored. We conducted a five-year vegetable field experiment and established four nitrogen-equivalent fertilization treatments: mineral fertilizer alone, and organic fertilizer substituting a quarter, half, and entirety of the mineral nitrogen. Employing a specialized multi-level fuzzy comprehensive evaluation model, our study assessed impacts of different organic substitution ratios on soil qualities, microbial diversity, vegetable yield and quality, environmental risks, and economic benefits in sustainable vegetable production of eastern China. Our results showed that the 50% organic substitution was optimal, significantly improving soil qualities and microbial characteristics, particularly in the topsoil layer. Compared to the control, this approach significantly reduced methane by 6.6–48.3%, nitrous oxide by 49.5–79.1%, and nitric oxide by 36.5–50.0%, while enhancing vegetable yield by 16.0–28.3% and its five-year average stability as well as quality as evidenced by increased protein, soluble sugar, and vitamin C contents. Economic analysis revealed that while it maximized environmental benefits, complete organic substitution did not consistently yield positive economic returns. In contrast, a 50% substitution ratio was identified as the most economically viable, representing a sustainable compromise that balances environmental health with economic feasibility. Further modeling analysis indicated an optimal comprehensive range between 42.9% and 64.5% for achieving the best balance of multiple objectives in vegetable fields. The study underscores the intricate organic substitution effects on intensive vegetable production, highlighting the necessity for tailored organic substitution strategies that integrate environmental sustainability with agricultural productivity and economic practicality.

Ungulate herbivores promote contrasting modifications of soil properties and organic carbon stabilization in a grazed grassland versus rewilded woodland environment

Large vertebrate herbivores are ecosystem engineers, provoking cascading effects on soil properties through modifications of plant communities as well as direct modulation of organic matter incorporated into soils. However, most studies have been carried out with domestic ungulates in grasslands, and the effects which predominate in grasslands may not be generalizable to other ecosystems. It is not well understood how trophic rewilding with wild ungulates may affect soil processes, especially in non-grassland systems albeit rewilding of natural areas is a process associated with larger trends of land abandonment, shrub encroachment or land use change. In this study we investigated ungulate herbivore exclusion in two geographically and pedo-climatically equivalent but ecologically distinct contexts: a Mediterranean grassland with domesticated herbivores, and a reforested area populated by a community of wild ungulates. In each context, long-term herbivore exclusion zones were used to understand the effect of herbivores on soil properties and particularly on soil organic carbon (SOC). Samples from the topsoil (0–5 cm) were taken inside and outside the exclosures distributed between the two contexts, and ecosystem-level effects and responses to grazing were investigated. We found that soil properties’ response to grazing depended on the ecological context in which the grazing occurred. SOC contents in the grassland increased by up to 37% with grazing, while grazing reduced SOC concentrations by 23% in the rewilded area. In both cases, grazing was also associated with significant alterations of soil microbial biomass, the microbial metabolic quotient (qCO2), and aggregate stability, but the effects were opposite: On one hand, domesticated herbivores in the grassland positively influenced carbon stabilization which was strongly associated with soil microbial processes and characteristics, and additionally the proportion of stable macroaggregates was increased. In contrast, wild ungulate herbivory in the forest ecosystem reduced SOC concentrations, accompanied by decreased microbial biomass and increased microbial maintenance costs, and stable macroaggregates were reduced. The results indicate the importance of ecological context in determining the effect of herbivores on soil properties and processes and suggest that the directionality of effects on SOC may change owing to the predominance of different mechanisms of SOC stabilization. Consequently, this study provides evidence that the management of ungulates in rangelands or forests can be associated with different outcomes as related to crucial soil properties such as SOC contents and aggregation.

The potential of soil microbial communities to transform deoxynivalenol in agricultural soils-a soil microcosm study.

Infestation of cereal fields with toxigenic Fusarium species is identified as an environmental source for the mycotoxin deoxynivalenol (DON). During rain events, DON may be washed off from infested plants and enter the soil, where microbial transformation may occur. Although some studies showed DON transformation potential of soil microbial communities in liquid soil extracts, these findings can not be transferred to environmental conditions. Accordingly, microbial transformation of DON in soil has to be investigated under realistic conditions, e.g., microcosms mimicking field situations. In this study, we investigated the potential of soil microbial communities to transform DON in six different agricultural soils at two levels (0.5 and 5 µg g-1). The dissipation and the formation of transformation products were investigated in a period of 35 days and compared to a sterilized control. In addition, we measured soil respiration and applied the phospholipid-derived fatty acid (PLFA) analysis to assess whether soil microbial community characteristics are related to the microbial transformation potential. Dissipation of DON in non-sterilized soils was fast (50% dissipation within 0.6-3.7 days) compared to the sterile control where almost no dissipation was observed. Thus, dissipation was mainly attributed to microbial transformation. We verified that small amounts of DON are transformed to 3-keto-deoxynivalenol (3-keto-DON) and 3-epi-deoxynivalenol (3-epi-DON), which were not detectable after 16-day incubation, indicating further transformation processes. There was a trend towards faster transformation in soils with active and large microbial communities and low fungi-to-bacteria ratio.

Soil Microbial Community Structure and Functional Diversity Character of Abandoned Farmland in Minqin Oasis

To clarify the impact of the structure and function of soil microbial communities in the stage of abandoned farmland, three different stages of land abandoned in desert oasis areas were selected as the research objects. We used metagenomic sequencing technology to research soil microbial community structure and functional diversity characteristics of different stages of abandoned farmland. The results showed that there were significant differences in the relative abundance of the dominant phyla Actinobacteria, Proteobacteria, and Gemmatimonadetes in the soil of the three stages of returning farmland. Compared with that in the early stage of abandoned farmland, the later stage of abandoned farmland restoration increased the gene proportion involved in Quorum sensing, porphyrin and chlorophyll metabolism, pantothenate and CoA biosynthesis, and styrene degradation, and there was a significant difference in relative abundance (P<0.05), which indicated that different stages of abandoned farmland had changed the functional potential of the nutrient cycle and energy metabolism in soil microbial communities. The RDA results showed that EC, AK, and TN had a significant impact on the functional composition of soil microbes, and soil EC had the greatest impact on microbial functional composition. The results showed that different stages of abandoned farmland had a significant impact on the soil microbial community structure and functional composition. In the ecological restoration of abandoned farmland in Minqin Oasis, the sensitivity of microbial community structure and functional composition to soil restoration at different stages should be considered using comprehensive relevant indicators.

Variations in Soil Organic Carbon Fractions and Microbial Community in Rice Fields under an Integrated Cropping System

Combining rice cultivation and aquaculture into an integrated cropping system is a management approach that enhances the sustainability of rice fields. However, how soil characteristics influence soil microbial community characteristics following implementation of such an integrated system, particularly in the waterlogged paddies of the Pearl River Delta, is poorly understood. An integrated cropping system (rice–fish–duck integrated cropping system, RFD) and a rice–pepper rotation system (RPS) were compared using a conventional rice cropping system (CRS) as a reference. We used phospholipid-derived fatty acid (PLFA) analysis to assess soil microbial community structure and function and measured soil nutrient content and organic carbon fractions. Our results indicated that the soil nutrient content, organic carbon fractions, and C-hydrolyzing activities differed among the cropping systems. The RFD resulted in higher microbial PLFA concentrations and a lower ratio of Gram-positive to Gram-negative bacteria than CRS. Additionally, the integrated system reduced microbial nutrient stress by increasing soil pH. Further analysis revealed that active soil organic carbon significantly affected the soil microbial community. Thus, the RFD integrated cropping systems that alter the combined actions of pH and active organic carbon fractions can be used to improve soil microbial communities.

The Impact and Determinants of Mountainous Topographical Factors on Soil Microbial Community Characteristics.

Soil bacterial and fungal community communities play significant ecological functions in mountain ecosystems. However, it is not clear how topographic factors and soil physicochemical properties influence changes in microbial community structure and diversity. This study aims to investigate how altitude and slope orientation affect soil physicochemical properties, soil microbial communities, and their contributing factors. The assessment was conducted using Illumina MiSeq sequencing in various altitude gradients and on slopes with different aspects (shady slopes and sunny slopes) in the subalpine meadow of Dongling Mountain, Beijing. Topographical factors had a significant effect on soil physicochemical properties: the primary factors determining the structure of microbial communities are total potassium (TK), ammonium nitrogen (NH4+-N), and soil organic carbon (SOC). There was no significant change in the diversity of the bacterial community, whereas the diversity of the fungal community displayed a single-peaked trend. The effect of slope orientation on microbial communities was not as significant as the effect of elevation on them. The number of bacterial communities with significant differences showed a unimodal trend, while the number of fungal communities showed a decreasing trend. The co-occurrence network of fungal communities exhibits greater intricacy than that of bacterial communities, and bacterial communities are more complex in soils with sunny slopes compared to soils with shady slopes, and the opposite is true for fungal communities. The identification of the main factors that control soil microbial diversity and composition in this study, provided the groundwork for investigating the soil microbial response and adaptation to environmental changes in subalpine meadows.

Positive Effects of Organic Amendments on Soil Microbes and Their Functionality in Agro-Ecosystems.

Soil microbial characteristics are considered to be an index for soil quality evaluation. It is generally believed that organic amendments replacing chemical fertilizers have positive effects on changing microbial activity and community structure. However, their effects on different agro-ecosystems on a global scale and their differences in different environmental conditions and experimental durations are unclear. This study performed a meta-analysis based on 94 studies with 204 observations to evaluate the overall effects and their differences in different experimental conditions and duration. The results indicated that compared to chemical fertilizer, organic amendments significantly increased total microbial biomass, bacterial biomass, fungal biomass, Gram-positive bacterial biomass and Gram-negative bacterial biomass, and had no effect on the ratio of fungi to bacteria and ratio of Gram-positive bacteria to Gram-negative bacteria. Meanwhile, land use type, mean annual precipitation and soil initial pH are essential factors affecting microbial activity response. Organic-amendment-induced shifts in microbial biomass can be predominantly explained by soil C and nutrient availability changes. Additionally, we observed positive relationships between microbial functionality and microbial biomass, suggesting that organic-amendment-induced changes in microbial activities improved soil microbial functionality.

Effects of slope aspect on soil enzyme activity and microbial nutrient limitation in subalpine region of wes-tern Sichuan, China.

Exploring the resource limitation of soil microbial metabolism is essential to understand ecosystem functions and processes. However, the spatially divergent patterns and drivers of soil microbial nutrient limitation cha-racteristics in montane ecosystems at small scales, especially at the slope aspect scale, are still unclear. In this study, we measured soil enzyme activities involved in carbon (C), nitrogen (N) and phosphorus (P) cycle and quantified the microbial nutrient limitations by enzyme stoichiometry in two representative mountain sites in subalpine region of western Sichuan, including the sunny and shady slopes with different vegetation types (shrubland and forest, respectively) in Miyaluo of Lixian County, and with the same vegetation type (shrubland) in Yakexia of Heishui County. The results showed that soil enzyme activities and their stoichiometric ratios were significantly different between slope aspects in Miyaluo, while the differences were not significant in Yakexia. The stoichiometry ratio of C-, N- and P-acquiring enzymes on the sunny slope of Miyaluo was 1:0.96:0.92, approaching the 1:1:1 ratio at the global scale, but deviated from 1:1:1 on the shady slope of Miyaluo (1:1.39:0.75) and the different slopes of Yakexia (1:1.09:1.35). There was no significant difference in vector length between slope aspects at both sites, indicating no significant effect of slope aspect on the microbial C limitation. The vector angle was significantly higher on the sunny slope (43.6°) than that on the shady slope (28.7°) in Miyaluo, suggesting that the microorganisms were mainly N-limited. Partial least squares path model showed that the vector angle was mainly directly influenced by the soil nutrient ratios. The vector angle ranged from 50.3° to 51.4°, and did not differ between slope aspects in Yakexia. Therefore, differences in vegetation types between slope aspects drove variations in soil enzyme activity and microbial nutrient limitation through soil properties. It would provide a scientific basis for predicting the spatial pattern of soil enzyme activity and microbial nutrient limitation.

Potentilla parvifolia strongly influenced soil microbial community and environmental effect along an altitudinal gradient in central Qilian Mountains in western China.

The Qilian Mountains (QLMs) form an important ecological security barrier in western China and a priority area for biodiversity conservation. Potentilla parvifolia is a widespread species in the mid-high altitudes of the QLMs and has continuously migrated to higher altitudes in recent years. Understanding the effects of P. parvifolia on microbial community characteristics is important for exploring future changes in soil biogeochemical processes in the QLMs. This study found that P. parvifolia has profound effects on the community structure and ecological functions of soil microorganisms. The stability and complexity of the root zone microbial co-occurrence network were significantly higher than those of bare soils. There was a distinct altitudinal gradient in the effect of P. parvifolia on soil microbial community characteristics. At an elevation of 3204 m, P. parvifolia promoted the accumulation of carbon, nitrogen, and phosphorus and increased sucrase activity and soil C/N while significantly improving the community richness index of fungi (p < .05) compared with that of bacteria and the relative abundance of Ascomycota. The alpha diversity of fungi in the root zone soil of P. parvifolia was also significantly increased at 3550 m altitude. Furthermore, the community similarity distance matrix of fungi showed an evident separation at 3204 m. However, at an altitude of 3750 m, P. parvifolia mainly affected the bacterial community. Potentilla parvifolia increased the bacterial community richness. This is in agreement with the findings based on the functional prediction that P. parvifolia favors the growth and enrichment of denitrifying communities at 3550 and 3750 m. The results provide a scientific basis for predicting the evolutionary trends of the effects of P. parvifolia on soil microbial communities and functions and have important implications for ecological governance in the QLMs.

Understory vegetation had important impact on soil microbial characteristics than canopy tree under N addition in a Pinus tabuliformis plantation

Forest ecosystem is a complex community, and its soil microbes play a vital role in global matter cycling. However, the patterns of rhizosphere soil microbial characteristics among tree-shrub-grass and their responses to nitrogen (N) deposition are still unclear. This study evaluated the microbial biomasses, processes (gas fluxes), and enzyme activities in the rhizosphere soils of tree (Pinus tabuliformis), shrub (Rosa xanthina), and grass (Carex lanceolata) and their responses to N addition (0, 3, 6, 9 g N m−2 y−1 corresponding to N0, N3, N6, N9) in a P. tabuliformis plantation. (1) Microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial biomass phosphorus (MBP) contents, as well as CO2, CH4 flux rates in the rhizosphere soil of C. lanceolata were significantly higher than those in the rhizosphere soils of P. tabuliformis and R. xanthina (P < 0.05). The activities of alkaline phosphatase (ALT), leucine aminopeptidase (LAP), β-glucosidase (BG), D-cellulosidase (CBH), N-acetyl-glucosaminidase (NAG), and xylosidase (XYL) in the rhizosphere soils of C. lanceolata and R. xanthina were significantly higher than those in the rhizosphere soil of P. tabuliformis. (2) Soil MBC content, N2O, and CH4 flux rates increased after N addition, while the CO2 flux rate decreased. MBP content initially increased and then reduced with N additions, and the maximum values observed in N3 or N9 treatments. (3) In the rhizosphere soil of P. tabuliformis, N addition enhanced the NAG, BG, CBH, and XYL activities. While low N increased and high N decreased these enzyme activities in the rhizosphere soils of C. lanceolata and R. xanthina, with the maximum values obtained in N3 treatment. (4) N addition directly reduced the CO2 flux rate and indirectly enhanced the gas flux rate by increasing soil MBC and MBP contents. Species change indirectly affected the microbial biomass and enzyme activity by altering soil chemical properties, which eventually affected gas flux rates. Our study emphasizes the effects of tree-shrub-grass on soil microbial characteristics, which can improve the evaluation of soil ecological processes and responses to N deposition in forest ecosystems.

Phytoremediation Effect and Soil Microbial Community Characteristics of Jiulong Iron Tailings Area, Jiangxi

The aim of this paper was to explore the remediation effect and mechanism of Wetland pine (Pinus elliottii), Chinese fir (Cunninghamia lanceolata (Lamb.) Hook), and Alder (Alnus cremastogyne Burkill) on heavy metal contaminated soil in the iron tailings of Jiulong Iron Tailings Area. At the same time, the specificity of plant rhizosphere and non-rhizosphere soil microbial community structure and ecological function were analyzed based on macrogenomic sequencing. The results showed that the dominant microbial genera in J1 (control) was Acidobacteria, followed by Proteobacteria and Actinobacteria. The microbial genera with the highest percentage of relative abundance in J2, J3, J4, J5, and J6 (J2, Wetland Pine rhizosphere; J3, Wetland Pine non-rhizosphere; J4, Chinese fir rhizosphere; J5, Alder rhizosphere; J6, Alder non-rhizosphere) were Proteobacteria, followed by Acidobacteria, and Actinobacteria. It was found that Proteobacteria promoted heavy metal solubilization, activated heavy metals, and converted their forms to improve plant uptake of heavy metals. This proves that the microorganisms of Proteobacteria are the key microbial genera in the study of regional heavy metal remediation. The antibiotic resistance genes (ARGs) in microorganisms can respond to the inducement of heavy metals. Here, we investigated the relationship between the abundance of soil microorganisms ARGs and heavy metal pollution in Jiulong Iron Tailings Area. There are significant differences in the quantity and category of ARGs in the rhizosphere and non-rhizosphere soil samples of the three tree species. The results of this study provide the foundation for the theory and practice of remediation of heavy metal contamination in soils of iron tailing areas in Jiulong Iron Tailings Area in similar stand conditions.

Effects of nano-TiO2/Fe3O4 addition on soil phosphorus fractions, microbial characteristics, and plant growth

Effects of nano-TiO2/Fe3O4 addition on soil phosphorus fractions, microbial characteristics, and plant growth