Soil Microbial Community Characteristics Research Articles

Soil microbial community characteristics and the influencing factors at different elevations on the eastern slope of Helan Mountain, Northwest China.

As an important bridge connecting aboveground communities and belowground biological processes, soil microorganisms play an important role in regulating belowground ecological processes. The altitudinal changes and driving factors of soil microbial community in mountain ecosystem in arid region are still unclear. We measured soil physicochemical properties at seven altitudes in the range of 1300-2800 m in Helan Mountains, and investigated the understory community composition, soil physicochemical properties, and soil microbial community. The driving factor for soil microbial community was explored by variance partitioning analysis and redundancy analysis. The results showed that the total amount of soil microorganisms and bacterial biomass first increased and then decreased with the increases of altitude, fungi, actinomyces, arbuscular mycorrhizal fungi, Gram-positive bacteria, and Gram-negative bacteria groups showed a gradual increase. The variation of fungal-to-bacterial ratio (F/B) along the altitude showed that the cumulative ability of soil bacteria was stronger than that of fungi at low altitudes, while the pattern is opposite at high altitudes. The ratio of Gram-positive bacteria to Gram-negative bacteria (GP/GN) showed an overall decreasing trend with the increases of altitude, indicating that soil bacteria and organic carbon availability changed from "oligotrophic" to "eutrophication" and from "low" to "high" transition as the altitude increased. Vegetation properties, soil physical and chemical properties jointly accounted for 95.7% of the variation in soil microbial community. Soil organic carbon (SOC), soil water content (SWC), and total nitrogen (TN) were significantly correlated with soil microbial community composition. Our results revealed the distribution pattern and driving factors of soil microbial communities at different elevations on the eastern slope of Helan Mountain, which would provide theoretical basis and data support for further understanding the interaction between plant-soil-microorganisms in arid areas.

Arsenic pollution from human activities drives changes in soil microbial community characteristics.

Soil arsenic (As) pollution not only decreases plant productivity but also soil quality, in turn hampering sustainable agricultural development. Despite the negative effects of As contamination on rice yield and quality being reported widely, the responses of microbial communities and co-occurrence networks in paddy soil to As pollution have not been explored. Here, based on high-throughput sequencing technologies, we investigated bacterial abundance and diversity in paddy soils with different levels of As contamination, and constructed associated microbial co-occurrence networks. As pollution reduced soil bacterial diversity significantly (p < 0.001). In addition, bioavailable As concentrations were negatively correlated with Actinobacteria and Acidobacteria relative abundance (p < 0.05). Conversely, As pollution had a positive relationship with Chloroflexi, Betaproteobacteria, and Bacteroidetes relative abundance (p < 0.05). Firmicutes relative abundance decreased with an increase in total As concentration. The ecological clusters and key groups in bacterial co-occurrence networks exhibited distinct trends with an increase in As pollution. Notably, Acidobacteria play an important role in maintaining microbial networks in As contaminated soils. Overall, we provide empirical evidence that As contamination influences soil microbial community structure, posing a threat to soil ecosystem health and sustainable agriculture.

Variations in soil microbial community structure and extracellular enzymatic activities along a forest-wetland ecotone in high-latitude permafrost regions.

Permafrost degradation by global warming is expected to alter the hydrological processes, which results in changes in vegetation species composition and gives rise to community succession. Ecotones are sensitive transition areas between ecosystem boundaries, attract particular interest due to their ecological importance and prompt responses to the environmental variables. However, the characteristics of soil microbial communities and extracellular enzymes along the forest-wetland ecotone in high-latitude permafrost region remain poorly understood. In this study, we evaluated the variations of soil bacterial and fungal community structures and soil extracellular enzymatic activities of 0-10 cm and 10-20 cm soil layers in five different wetland types along environmental gradients, including Larix gmelinii swamp (LY), Betula platyphylla swamp (BH), Alnus sibirica var. hirsute swamp (MCY), thicket swamp (GC), and tussock swamp (CC). The relative abundances of some dominant bacterial (Actinobacteria and Verrucomicrobia) and fungal (Ascomycota and Basidiomycota) phyla differed significantly among different wetlands, while bacterial and fungal alpha diversity was not strongly affected by soil depth. PCoA results showed that vegetation type, rather than soil depth explained more variation of soil microbial community structure. β-glucosidase and β-N-acetylglucosaminidase activities were significantly lower in GC and CC than in LY, BH, and MCY, while acid phosphatase activity was significantly higher in BH and GC than LY and CC. Altogether, the data suggest that soil moisture content (SMC) was the most important environmental factor contributing to the bacterial and fungal communities, while extracellular enzymatic activities were closely related to soil total organic carbon (TOC), nitrate nitrogen () and total phosphorus (TP).

Effects of the Transformation from Natural Alpine Grassland to Mixed Artificial Grassland on the Characteristics of Soil Microbial Community

This study aimed to analyze the effects of the transformation from natural alpine grassland (NAG) to mixed artificial grassland (MAG) on the characteristics of soil microbial community. We used Illumina Miseq high-throughput sequencing technology to investigate the soil microbial community of natural grassland and mixed artificial grassland. The results showed that plant diversity and the content of soil organic matter decreased significantly from NAG to MAG. In total, 29 and 11 phyla bacteria and fungi were detected, respectively. Compared with that in NAG, the Shannon indexes of the bacterial community increased significantly in MAG (from 9.51 to 9.89), whereas these differences were not significant between the NAG and MAG fungal community. The structure and composition of the soil microbial community showed significant differences between NAG and MAG. In addition, Mantel test results suggested that soil total organic matter, total nitrogen, and soil moisture were significantly correlated with variations in the bacterial community, and soil total organic matter and soil moisture were significantly correlated with variations in fungal community. The results of linear discriminant analysis (LEfSe) indicated that Atribacteria and Ascomycota microorganisms could be considered as the indicator groups for NAG, whereas Gemmata and Trichocomaceae microorganisms could be considered as the indicator groups for MAG. Tax4Fun2 results showed that the transition from NAG to MAG affected the utilization of different carbon sources by bacteria.

Characteristics of Soil Microbial Community in Different Habitats in the Process of Ecological Restoration of Haifeng Wetland in Guangdong

Soil microorganisms can respond to changes in wetland ecosystem quality and functional evolution sensitively. To explore the changes and response mechanisms of soil microorganisms under ecological restoration measures, the characteristics of the soil microbial community and their influencing factors were analyzed using high-throughput sequencing technology in four different habitats (revegetation area, native vegetation area, tidal creek, and tidal flat) during the ecological restoration process in Haifeng wetland in Guangdong. The results showed that:soil physicochemical properties of the four different habitats were significantly different; the contents of TC, TN, TOC, and TK in the tidal creek were significantly higher than those in the other habitats; and the contents of TC, TN, and TP in the revegetation restoration area were significantly higher than those in the tidal flat. The EC values in the tidal creeks and tidal flat were significantly higher than those in the revegetation area and the native vegetation area. The diversity index and abundance of soil bacteria in the tidal creek were the highest, and those in the vegetation restoration area were significantly higher than those in the bare flat. The archaea in the tidal creek were significantly more complex than those in the other three habitats, and the fungal community diversity index and abundance in the native vegetation area were significantly higher than those in the other areas, which had the most complex community structure. TN and TC were the main factors affecting the bacterial community, whereas TN and EC were the main factors affecting the archaea community, and pH, TN, and TP were the key factors affecting the fungal community. In conclusion, the planting of vegetation on the tidal flat increased the diversity and richness of the soil microbial community during the process of ecological restoration, indicating that it has resulted in positive feedback on ecological restoration so far. The results of this study can provide a theoretical basis for the selection of ecological restoration strategies for the tidal flat.

Structural Characteristics and Assembly Mechanisms of Soil Microbial Communities under Water-Salt Gradients in Arid Regions.

Exploring the structural characteristics of arid soil microbial communities and their assembly mechanisms is important for understanding the ecological characteristics of arid zone soils and promoting ecological restoration. In this study, we used Illumina high-throughput sequencing technology to study soils in the arid zone of the Lake Ebinur basin, determined the differences among soil microbial community structures in the study area under different water-salt gradients, and investigated the effects of environmental factors on microbial community structure and assembly mechanisms. The results show the following: the microbial community alpha diversity exhibited a significantly higher low water-salt gradient (L) than high water-salt gradient (H) and medium water-salt gradient (M). The pH was most strongly correlated with soil microbial community structure, where the alpha diversity indices of the bacterial community and fungal community were significantly negatively correlated with pH, and the Bray-Curtis distance of bacterial community was significantly positively correlated with pH (p < 0.05). The complexity of bacterial community co-occurrence networks showed a significantly higher L than H and M, and the complexity of fungal community co-occurrence network showed a significantly lower L than H and M. The cooperative relationship of H and M in the co-occurrence networks was stronger than that of the L, and the key species of the microbial co-occurrence network were different under different water-salt gradients. Stochastic processes dominated the assembly mechanism of the microbial community structure of soil, and the explanation rates of deterministic and stochastic processes were different under different water-salt gradients, with the highest explanation rate of stochastic processes on the L accounting for more than 90%. In summary, the soil microbial community structure and assembly mechanisms significantly differed across water-salt gradients, and these findings can help provide a reference for further research on soil microbiology in arid zones.

Changes in soil fertility and microbial communities following cultivation of native grassland in Horqin Sandy Land, China: a 60-year chronosequence

BackgroundGrassland conversion to cropland is a prevailing change of land use in traditionally nomadic areas, especially in the Mongolian Plateau. We investigated the effects of grassland conversion followed by continuous cultivation on soil properties and microbial community characteristics in Horqin Sandy Land, a typical agro-pastoral transition zone of Northern China. Soil samples were collected from the topsoil (upper 20 cm) across a 60-year cultivation chronosequence (5, 15, 25, 35 and 60 years) and unconverted native grassland. Soil physico-chemical properties were determined and high-throughput sequencing was used to assess microbial community diversity and composition.ResultsGrassland cultivation resulted in changes to soil properties in both the short and longer term. Initially, it significantly increased soil bulk density (BD), electrical conductivity (EC), soil total nitrogen (TN), available phosphorus (AP) and available potassium (AK) concentrations, while reducing soil water content (SWC) and soil organic carbon content (SOC). Over the next 35–55 years of continuous cultivation, the trend for most of these characteristics was of reversion towards values nearer to those of native grassland, except for SOC which remained highly depleted. Cultivation of grassland substantially altered soil microbial communities at phylum level but there was no significant difference in microbial α-diversity between native grassland and any cropland. However, soil bacterial and fungal community structures at phylum level in the croplands of all cultivation years were different from those in the native grasslands. Heatmaps further revealed that bacterial and fungal structures in cropland tended to become more similar to native grassland after 15 and 25 years of cultivation, respectively. Redundancy analysis indicated that SOC, EC and BD were primary determinants of microbial community composition and diversity.ConclusionsThese findings suggest that agricultural cultivation of grassland has considerable effects on soil fertility and microbial characteristics of Horqin Sandy Land. Intensive high-yield forage grass production is proposed as an alternative to avoid further native grassland reclamation, while meeting the grazing development needs in the ethnic minority settlements of eco-fragile regions.

Depth-dependent effects of tree species identity on soil microbial community characteristics and multifunctionality

Soil microbes play key roles that support forest ecosystem functioning, while their community characteristics are strongly determined by tree species identity. However, the majority studies primarily focus on soil microorganisms in the topsoil, resulting in limited understanding of the linkages between tree species identity and the microbial communities that inhabit deep soils. Here we investigated the diversity, structure, function, and co-occurrence networks of soil bacterial and fungal communities, as well as related soil physicochemical properties, to a depth of two meters in dryland forests dominated by either Pinus tabuliformis, a native coniferous species, Robinia pseudoacacia, an exotic broadleaf and nitrogen-fixing species, or both. Tree species identity had stronger effects on soil multifunctionality and microbial community structure in the deep layers (80–200 cm) than in the top layers (0–60 cm). In addition, fungal communities were more responsive to tree species identity, whereas bacteria were more sensitive to soil depth. Tree species identity strongly influenced microbial network stability and complexity, with higher quantities in R. pseudoacacia than the other plantations, by affecting microbial composition and their associations. The increased in microbial network complexity and the relative abundance of keystone taxa enhance the soil multifunctionality of microbial productivity, sugar and chitin degradation, and nutrient availability and cycling. Meanwhile, the relative abundance of keystone taxa was more representative of soil multifunctionality than microbial diversity. Our study highlights that tree species identity significantly influences soil microbial community characteristics and multifunctionality, especially in deep soils, which will help us understand soil nutrients processed in plantation forest ecosystem and provide a reference for tree species selection in ecological restoration.

Long-term Tillage Alters Soil Properties and Rhizosphere Bacterial Community in Lime Concretion Black Soil under Winter Wheat–Summer Maize Double-Cropping System

Tillage practices can directly affect soil quality, influencing soil properties, crop growth, and soil microbial community characteristics. However, the influence of long-term tillage practices on the rhizosphere bacterial community in lime concretion black soil remains largely unknown. In this study, the effects of nine-year rotary tillage (RT), no-tillage (NT), subsoiling tillage (ST), and plow tillage (PT) on soil chemical properties, microbial community structure, and correlations between bacterial communities and soil properties in the maize rhizosphere were investigated. The results revealed that the maize yield in ST and PT was higher by 10.61% and 10.26% than that in RT and by 10.25% and 9.90% than that in NT, respectively. The soil organic matter (SOM) and total nitrogen (TN) contents in NT and ST were significantly higher than those in RT and PT, whereas the available phosphorus (AP) content in ST and PT was significantly higher than that in NT and RT. The diversity and richness of the soil bacterial communities exhibited a trend of NT &gt; RT &gt; PT &gt; ST. The principal component analysis revealed that the soil bacterial community differed among treatments. Linear discriminant analysis effect size (LEfSe) analysis demonstrated that Proteobacteria, Armatimonadetes, Verrucomicrobia, and Chloroflexi could serve as crucial biomarkers. Phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) results revealed that genes involved in carbon, lipid, and xenobiotic metabolism were enriched under ST and PT, whereas those involved in nitrogen and carbon fixation were enriched under NT. Besides, Proteobacteria, Verrucomicrobia, and Armatimonadetes were positively associated with AP levels and negatively associated with pH; however, Acidobacteria, Bacteroidetes, and Planctomycetes exhibited an opposite trend. Overall, ST and PT improved the soil properties and environmental suitability by increasing the bacterial keystone taxa; thus, these practices improved crop yield. These findings could enhance our understanding of the rhizosphere functional microbial community in lime concretion black soil for winter wheat–summer maize double-cropping system.

Grazing Regulates Changes in Soil Microbial Communities in Plant-Soil Systems

Soil microorganisms promote material transformation and energy flow in the entire ecological environment and play a key role in the stability and development of grassland ecosystems. Studies on the impacts of grazing on the soil microbial community and the establishment of a reasonable grazing intensity are crucial to improve our knowledge of the mechanisms underlying grassland degradation and to accurately assess the influence of grazing management on grassland functions and the nutrient cycle. Based on the grassland grazing control experimental platform, we compared the structure and diversity characteristics of soil microbial communities under six grazing intensities (0.00, 0.23, 0.34, 0.46, 0.69, and 0.92 AU ha−1) (1 AU = 500 kg of adult cattle) on the Hulunbuir Leymus chinensis meadow steppe. The results showed that soil microbial biomass carbon (MBC) and nitrogen (MBN) decreased with increasing soil depth. The 0–10 cm soil layer of G0.34 had the highest MBC and MBN, and the G0.92 treatment had the lowest MBC and MBN. Heavy grazing significantly decreased the MBC and MBN contents in the soil surface layer. The soil bacterial diversity under light grazing treatment (0.23 AU ha−1) was higher than that under heavy grazing, and the fungal diversity under the no-grazing treatment was higher than that under the grazing treatment. Overgrazing reduced the bacterial species in the soil. The plant belowground biomass significantly (p = 0.039) influenced the bacterial community structure, and the soil pH (p = 0.032), total nitrogen (p = 0.011), and litter (p = 0.007) significantly influenced the fungal community. The effects of grazing on microbial communities were primarily driven by vegetation productivity, litter mass, and soil geophysical and chemical characteristics. This study deepened our understanding of the impacts of grazing practices on soil microbial communities on the meadow steppe, suggesting that moderate-disturbance grazing can promote the sustainable development of grassland vegetation-soil microorganisms.

Distribution characteristics of soil microbial communities and their responses to environmental factors in the sea buckthorn forest in the water-wind erosion crisscross region.

Soil microorganisms are an important part of forest ecosystems, and their community structure and ecological adaptations are important for explaining soil material cycles in the fragile ecological areas. We used high-throughput sequencing technology to examine the species composition and diversity of soil bacterial and fungal communities in sea buckthorn forests at five sites in the water-wind erosion crisscross in northern Shaanxi (about 400 km long). The results are described as follows: (1) The soil bacterial community of the sea buckthorn forest in the study region was mainly dominated by Actinobacteria, Proteobacteria, and Acidobacteria, and the fungi community was mainly dominated by Ascomycota. (2) The coefficient of variation of alpha diversity of microbial communities was higher in the 0-10 cm soil layer than in the 10-20 cm soil layer. (3) Soil electrical conductivity (36.1%), available phosphorous (AP) (21.0%), available potassium (16.2%), total nitrogen (12.7%), and the meteorological factors average annual maximum temperature (33.3%) and average annual temperature (27.1%) were identified as the main drivers of structural changes in the bacterial community. Available potassium (39.4%), soil organic carbon (21.4%), available nitrogen (AN) (13.8%), and the meteorological factors average annual maximum wind speed (38.0%) and average annual temperature (26.8%) were identified as the main drivers of structural changes in the fungal community. The explanation rate of soil factors on changes in bacterial and fungal communities was 26.6 and 12.0%, respectively, whereas that of meteorological factors on changes in bacterial and fungal communities was 1.22 and 1.17%, respectively. The combined explanation rate of environmental factors (soil and meteorological factors) on bacterial and fungal communities was 72.2 and 86.6%, respectively. The results of the study offer valuable insights into the diversity of soil microbial communities in the water-wind erosion crisscross region and the mechanisms underlying their interaction with environmental factors.

Characteristics of soil microbial communities in farmland with different comprehensive fertility levels in the Panxi area, Sichuan, China.

Soil bacterial communities are intricately linked to ecosystem functioning, and understanding how communities assemble in response to environmental change is ecologically significant. Little is known about the assembly processes of bacteria communities across agro-ecosystems, particularly with regard to their environmental adaptation. To gain further insights into the microbial community characteristics of agro-ecosystems soil in the Panxi area of Sichuan Province and explore the key environmental factors driving the assembly process of the microbial community, this study conducted field sampling in major farmland areas of Panxi area and used Illumina MiSeq high-throughput sequencing technology to conduct bacterial sequencing. Soil organic matter (SOM), alkali-hydrolyzed nitrogen (AN), available phosphorus (AP), available potassium (AK) and other environmental factors were determined. The membership function method and principal component analysis method were used to evaluate the fertility of the soil. The results revealed minimal differences in alpha diversity index among samples with different comprehensive fertility indices, while NMDS analysis showed that community differences between species were mainly reflected in high fertility and low fertility (R: 0.068, p: 0.011). Proteobacteria, Acidobacteria and Actinobacteria were the main types of microbial communities, accounting for more than 60% of the relative abundance. Proteobacteria accounted for a higher proportion in the high fertility samples, while Acidobacteria and Actinobacteria accounted for a higher proportion in the middle and low fertility samples. Both the neutral theoretical model and zero model analysis showed that the microbial communities in tobacco-planting soil with different comprehensive fertility indices presented a random assembly process. With the increase in environmental distance difference, the diversity of the microbial community in medium and low-fertility soil also increased, but there was no significant change in high-fertility soil. Redundancy analysis showed that pH and SOM were the key factors affecting microbial community composition. The results of this study can provide a theoretical reference for the study of environmental factors and microbial communities in tobacco-growing soil.

Characteristics of Soil Physicochemical Properties and Microbial Community of Mulberry (Morus alba L.) and Alfalfa (Medicago sativa L.) Intercropping System in Northwest Liaoning

Medicinal plant intercropping is a new intercropping method. However, as a new intercropping model, the influence of intercropping of alfalfa on microorganisms has not been clarified clearly. In this study, the composition and diversity of microbial communities in alfalfa intercropping were studied, and the differences of bacterial and fungal communities and their relationships with environmental factors are discussed. Intercropping significantly decreased soil pH and significantly increased soil total phosphorus (TP) content, but did not increase soil total carbon (TC) and total nitrogen (TN). Intercropping can increase the relative abundance of Actinobacteria and reduce the relative abundance of Proteobacteria in soil. The relative abundance and diversity of bacteria were significantly correlated with soil pH and TP, while the diversity of fungi was mainly correlated with TC, TN and soil ecological stoichiometry. The bacterial phylum was mainly related to pH and TP, while the fungal phylum was related to TC, TN, C: P and N: P. The present study revealed the stoichiometry of soil CNP and microbial community characteristics of mulberry-alfalfa intercropping soil, clarified the relationship between soil stoichiometry and microbial community composition and diversity, and provided a theoretical basis for the systematic management of mulberry-alfalfa intercropping in northwest Liaoning.

Effects of soil microbial community characteristics on soil multifunctionality in sand-fixation shrublands

Effects of soil microbial community characteristics on soil multifunctionality in sand-fixation shrublands

Functional Diversity of Soil Microorganisms and Influencing Factors in Three Typical Water-Conservation Forests in Danjiangkou Reservoir Area

As a key part of the forest ecosystem, soil microorganisms play extremely important roles in maintaining the ecological environment and the security of water quality in reservoir areas. However, it is not clear whether there are differences in the functional diversity of soil microorganisms in different types of water-conservation forests in reservoir areas, and which factors affect the functional diversity of soil microorganisms. In our study, the Biolog-Eco microplate technique was used to analyze the carbon source metabolic characteristics of soil microbial communities in three typical water-conservation forests and a non-forest land: Pinus massoniana-Quercus variabilis mixed forest (MF), Pinus massoniana forest (PF), Quercus variabilis forest (QF) and non-forest land (CK). The results showed that the average well color development (AWCD), the Shannon diversity index (SDI) and the richness index (S) of the three forest lands was significantly greater than that of the non-forest land (p &lt; 0.05). The mean values of AWCD, SDI and S of the three forests had the same order (QF &gt; PF &gt; MF), but there was no significant difference among different types of forests. The microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) of QF and PF were higher than those of MF and CK, but the microbial biomass C/N ratio (MBC/MBN) was lower. The variance partitioning analysis (VPA) showed that 86.4% of the variation was explained by plant (community) diversity, soil physical and chemical properties and soil microbial biomass, which independently explained 10.0%, 28.9%, and 14.9% of the variation, respectively. The redundancy analysis (RDA) showed that total phosphorus (TP), microbial biomass carbon (MBC), total nitrogen (TN), number of plant species (Num) and alkali-hydro nitrogen (Wn) were the key factors affecting the functional diversity of soil microorganisms. This study confirmed that forest ecosystem is better than non-forest land in maintaining soil microbial function diversity. Moreover, Quercus variabilis forest may be a better stand type in maintaining the diversity of soil microbial functions in the study area.

Metagenomic insights into the characteristics of soil microbial communities in the decomposing biomass of Moso bamboo forests under different management practices.

Considering the rapid growth and high biomass productivity, Moso bamboo (Phyllostachys edulis) has high carbon (C) sequestration potential, and different management practices can strongly modify its C pools. Soil microorganisms play an important role in C turnover through dead plant and microbial biomass degradation. To date, little is known about how different management practices affect microbial carbohydrate-active enzymes (CAZymes) and their responses to dead biomass degradation. Based on metagenomics analysis, this study analyzed CAZymes in three comparable stands from each Moso bamboo plantation: undisturbed (M0), extensively managed (M1), and intensively managed (M2). The results showed that the number of CAZymes encoding plant-derived component degradation was higher than that encoding microbe-derived component degradation. Compared with the M0, the CAZyme families encoding plant-derived cellulose were significantly (p < 0.05) high in M2 and significantly (p < 0.05) low in M1. For microbe-derived components, the abundance of CAZymes involved in the bacterial-derived peptidoglycan was higher than that in fungal-derived components (chitin and glucans). Furthermore, M2 significantly increased the fungal-derived chitin and bacterial-derived peptidoglycan compared to M0, whereas M1 significantly decreased the fungal-derived glucans and significantly increased the bacterial-derived peptidoglycan. Four bacterial phyla (Acidobacteria, Actinobacteria, Proteobacteria, and Chloroflexi) mainly contributed to the degradation of C sources from the plant and microbial biomass. Redundancy analysis (RDA) and mantel test suggested the abundance of CAZyme encoding genes for plant and microbial biomass degradation are significantly correlated with soil pH, total P, and available K. Least Squares Path Modeling (PLS-PM) showed that management practices indirectly affect the CAZyme encoding genes associated with plant and microbial biomass degradation by regulating the soil pH and nutrients (total N and P), respectively. Our study established that M2 and M1 impact dead biomass decomposition and C turnover, contributing to decreased C accumulation and establishing that the bacterial community plays the main role in C turnover in bamboo plantations.

Structural and functional characteristics of soil microbial communities in response to different ecological risk levels of heavy metals.

The potential ecological risk index (RI) is the most commonly used method to assess heavy metals (HMs) contamination in soils. However, studies have focused on the response of soil microorganisms to different concentrations, whereas little is known about the responses of the microbial community structures and functions to HMs at different RI levels. Here, we conducted soil microcosms with low (L), medium (M) and high (H) RI levels, depending on the Pb and Cd concentrations, were conducted. The original soil was used as the control (CK). High-throughput sequencing, qPCR, and Biolog plate approaches were applied to investigate the microbial community structures, abundance, diversity, metabolic capacity, functional genes, and community assembly processes. The abundance and alpha diversity indices for the bacteria at different RI levels were significantly lower than those of the CK. Meanwhile, the abundance and ACE index for the fungi increased significantly with RI levels. Acidobacteria, Basidiomycota and Planctomycetes were enriched as the RI level increased. Keystone taxa and co-occurrence pattern analysis showed that rare taxa play a vital role in the stability and function of the microbial community at different RI levels. Network analysis indicates that not only did the complexity and vulnerability of microbial community decrease as risk levels increased, but that the lowest number of keystone taxa was found at the H level. However, the microbial community showed enhanced intraspecific cooperation to adapt to the HMs stress. The Biolog plate data suggested that the average well color development (AWCD) reduced significantly with RI levels in bacteria, whereas the fungal AWCD was dramatically reduced only at the H level. The functional diversity indices and gene abundance for the microorganisms at the H level were significantly lower than those the CK. In addition, microbial community assembly tended to be more stochastic with an increase in RI levels. Our results provide new insight into the ecological impacts of HMs on the soil microbiome at different risk levels, and will aid in future risk assessments for Pb and Cd contamination.

Response Characteristics of Soil Microbial Community Under Long-term Film Mulching

Film mulching is an important practice to increase the yield and income in agricultural production. Soil samples were collected from four farmland sites with different mulching years to reveal the effect of long-term plastic mulching on characteristics of soil microbial community structure. In order to explore the long-term effect of soil microbial community change and its effect on the microbial ecological environment, high-throughput sequencing technology was used to analyze the changes in soil bacterial and fungal community structure. The results showed that long-term film mulching had no significant effect on soil bacterial diversity but decreased fungal diversity. Long-term film mulching decreased the abundance of Acidobacteriota and Mortierellomycetes and increased the abundance of Actinobacteriota. Long-term film mulching enriched the beneficial microbial communities such as Bacillus, Nocardioidaceae, Aspergillus, and Hypocreales in soil. However, long-term film mulching indued a simple and fragile soil fungal co-occurrence network pattern. The unidentified Sordariales under Ascomycota was the only key species in the fungal co-occurrence network, which resulted in potential risks to the ecological environment of the farmland soil. This study provided a theoretical basis for further understanding the effects of long-term film mulching on the ecological and environmental effects of microorganisms in farmland.

Soil chemistry and fungal communities are associated with dieback in an Endangered Australian shrub

Background and aimsField surveys across known populations of the Endangered Persoonia hirsuta (Proteaceae) in 2019 suggested the soil environment may be associated with dieback in this species. To explore how characteristics of the soil environment (e.g., pathogens, nutrients, soil microbes) relate to dieback, a soil bioassay (Experiment 1) was conducted using field soils from two dieback effected P. hirsuta populations. Additionally, a nitrogen addition experiment (Experiment 2) was conducted to explore how the addition of soil nitrogen impacts dieback.MethodsThe field soils were baited for pathogens, and soil physiochemical and microbial community characteristics were assessed and related to dieback among plants in the field and nursery-grown plants inoculated with the same field soils. Roots from inoculated plants were harvested to confirm the presence of soil pathogens and root-associated endophytes. Using these isolates, a dual culture antagonism assay was performed to examine competition among these microbes and identify candidate pathogens or pathogen antagonists.ResultsDieback among plants in the field and Experiment 1 was associated with soil physiochemical properties (nitrogen and potassium), and soil microbes were identified as significant indicators of healthy and dieback-affected plants. Plants in Experiment 2 exhibited greater dieback when treated with elevated nitrogen. Additionally, post-harvest culturing identified fungi and other soil pathogens, some of which exhibited antagonistic behavior.ConclusionThis study identified candidate fungi and soil physiochemical properties associated with observed dieback and dieback resistance in an Endangered shrub and provides groundwork for further exploring what drives dieback and how it can be managed to promote the conservation of wild populations.

Response of Soil Microbial Community Composition and Diversity at Different Gradients of Grassland Degradation in Central Mongolia

Vegetation and soil microorganisms are important components of terrestrial ecosystems and play a crucial role in ecosystem functioning. However, little is known about the synergistic changes in soil microbial community with aboveground plants in grassland degradation and the role of the microbial community in the process of vegetation restoration succession. In this study, we investigated the characteristics of soil microbial communities and diversities in the different levels of grassland degradation using Illumina MiSeq high-throughput sequencing. The dominant bacteria phyla were: Actinobacteriota, 31.61–48.90%; Acidobacteriota, 7.19–21.73%; Chloroflexi, 9.08–19.09%; and Proteobacteria, 11.14–18.03%. While the dominant fungi phyla were: Ascomycota, 46.36–81.58%; Basidiomycota, 5.63–33.18%; and Mortierellomycota, 1.52–37.69%. Through RDA/CCA, the effects of environmental factors on the differences in the soil microbial community between different sites were interpreted. Results showed that the pH was the most critical factor affecting soil microbial communities in seriously degraded grassland; nevertheless, soil microbial communities in non-degraded grassland and less degraded grasslands were mainly affected by the soil moisture content and soil enzyme activities (sucrase activity, alkaline phosphatase activity and catalase activity). We systematically demonstrated the soil microbial communities of different grassland degradation gradients in Mongolia, which provided valuable information for grassland degradation reduction and vegetation restoration succession.