Soil microbial community composition and co-occurrence network responses to mild and severe disturbances in volcanic areas

The effects of polycyclic aromatic hydrocarbons on ecological assembly processes and co-occurrence patterns differ between soil bacterial and fungal communities

Polycyclic aromatic hydrocarbons (PAHs) are hazardous organic pollutants prevalent in soil ecosystems. Bacteria and fungi play important roles in the degradation of PAHs in the soils. However, little is known about the differences between the bacterial and fungal community assemblies in PAH-contaminated soils. In this study, soil bacterial and fungal community distributions were investigated in maize farmlands and roadside barelands around nine coking plants in Shanxi, China. Most of the soil samples were severely polluted with PAHs. A clear microbial biogeographic pattern was observed. Bacterial communities are primarily affected by environmental factors, whereas fungal communities are primarily affected by spatial factors. Null modeling showed that homogeneous selection (deterministic processes) and dispersal limitation (stochastic processes) dominated the bacterial and fungal community assemblages, respectively. PAH concentrations were closely linked to community assembly processes, and influenced microbial co-occurrence by mediating specific network modules. Overall, the effects of PAHs on bacterial community assembly and co-occurrence relationships were greater than those on fungal communities. Some microbial taxa associated with PAH degradation can be considered potential biomarkers that reflect the degree of PAH pollution. These results expand the understanding of the mechanisms underlying the assembly and maintenance of soil microbial communities in response to PAH contamination.

Forest Soil pH and Dissolved Organic Matter Aromaticity Are Distinct Drivers for Soil Microbial Community and Carbon Metabolism Potential

The ecological niche separation of microbial interactions in forest ecosystems is critical to maintaining ecological balance and biodiversity and has yet to be comprehensively explored in microbial ecology. This study investigated the impacts of soil properties on microbial interactions and carbon metabolism potential in forest soils across 67 sites in China. Using redundancy analysis and random forest models, we identified soil pH and dissolved organic matter (DOM) aromaticity as the primary drivers of microbial interactions, representing abiotic conditions and resource niches, respectively. Our network comparison results highlighted significant differences in microbial interactions between acidic and non-acidic soils, suggesting the critical influences of abiotic conditions on microbial interactions. Conversely, abiotic resource niches played a more pivotal role in shaping the carbon metabolism of soil microbes, supporting the concept that resource niche-based processes drive microbial carbon cycling. Additionally, we demonstrated that microbial interactions contributed significantly to ecosystem function stability and served as potential ecological indicators of microbial functional resilience under environmental stress. These insights emphasize the critical need to preserve microbial interactions for effective forest ecosystem management and projection of ecological outcomes in response to future environmental changes.

Response of Soil Bacteria to Short-Term Nitrogen Addition in Nutrient-Poor Areas

Increasing nitrogen (N) addition induces soil nutrient imbalances and is recognized as a major regulator of soil microbial communities. However, how soil bacterial abundance, diversity, and community composition respond to exogenous N addition in nutrient-poor and generally N-limited regions remains understudied. In this study, we investigated the effects of short-term exogenous N additions on soil bacterial communities using quantitative polymerase chain reaction (PCR) and Illumina Miseq sequencing in an in situ N addition field experiment. The results showed that a low nitrogen addition increased the observed species (Sobs) of the bacterial community, and with the increased nitrogen addition, the Sobs of bacteria gradually decreased, especially the unique OTUs. The relative abundance of Proteobacteria, Actinobacteria, and Gemmatimonadetes increased with increasing nitrogen addition, whereas the relative abundance of Chloroflexi and Firmicutes decreased. Soil properties play an important role in bacterial community structure at phylum or genus levels. Short-term nitrogen addition increased the proportion of nodes from Actinobacteria and Proteobacteria in the co-occurrence network and enhanced the stability of the microbial network. Actinobacteria may play an important role in constructing the network. Our study aims to explore the effects of nitrogen addition on the diversity, composition, and structure of soil bacterial communities in nutrient-poor areas caused by ecological disturbances.

Effects of volcanic environment on Setaria viridis rhizospheric soil microbial keystone taxa and ecosystem multifunctionality

Keystone taxa are significant within ecosystem multifunctionality, as certain species fulfil essential functions such as recycling soil nutrients, promoting plant growth, influencing biogeochemical processes, and contributing to human health maintenance. However, there are still gaps regarding the relationship between microbial communities in volcanic rhizospheric soil and ecosystem multifunctionality. As a result, in this research, we employed Illumina MiSeq high-throughput sequencing to analyse the microbial community composition of rhizospheric soil from volcanic S. viridis. Compared with non-volcanic areas, volcanic soils have higher fungal alpha diversity and the absolute abundance of bacteria (16S gene copies) showed significant variation between the two successions (P < 0.0001). The network analysis further demonstrated that the microbial diversity in non-volcanic regions surpassed that of the volcanic area. The volcanic fungi network has more nodes and edges, is more complex than non-volcanic areas (Nodes: 425 vs. 770; Edges: 21844 vs. 74532), and more rhizosphere growth-promoting bacteria are enriched. Regression analysis and correlation networks showed that fungal communities were more closely associated with ecosystem multifunctionality than bacteria. This study lays the groundwork for examining the microbial keystone taxa in the rhizosphere of volcanic plants and offers valuable insights into the multifaceted functions of plant rhizospheric soil ecosystems.

Spatiotemporal distribution patterns and assembly mechanisms of eukaryotic plankton communities in Liujiaxia Reservoir at the northeastern edge of the Tibetan Plateau

Eukaryotic plankton are important parts of the aquatic ecosystem and their community composition and spatiotemporal distribution patterns are affected by environmental factors. The Liujiaxia Reservoir is located at the northeastern edge of the Tibetan Plateau and is a vital resource for communities and agriculture in the region. Revealing the plankton diversity and their correlation with environmental factors is essential for understanding the ecological processes and mechanisms by which plankton contribute to, and maintain the ecosystem function of, the Liujiaxia Reservoir and beyond. This study investigated the detailed spatiotemporal distribution patterns and assembly mechanisms of eukaryotic plankton communities in Liujiaxia Reservoir for three periods during 2021. Significant spatial and temporal variations of abundance and community distribution of eukaryotic plankton were demonstrated. In addition, environmental factors such as water transparency, total phosphorus, total nitrogen, ammonia nitrogen, and pH were confirmed to have the most significant impact on the distribution of these communities in the reservoir. The dominant eukaryotic plankton group was Pyrrophyta, and the species interactions were predominantly cooperative. The trophic level index indicated excellent overall water quality in the reservoir. Deterministic processes were demonstrated as the predominant factors governing the assembly of eukaryotic plankton communities. This study provides valuable insight into the eukaryotic plankton community structure in the Liujiaxia Reservoir and reveals the complex relationships between plankton communities, environmental factors, and water quality.IMPORTANCEBased on 18S rDNA high-throughput sequencing, the spatiotemporal distribution patterns and assembly mechanisms of eukaryotic plankton communities were investigated. This study provides valuable insight into the eukaryotic plankton community structure in the Liujiaxia Reservoir in the northeastern edge of the Tibetan Plateau, and the relationships between eukaryotic plankton communities, environmental factors, and water quality. Through the dynamic changes of these communities, the water quality of the reservoir was assessed to provide basic data for the protection of its biodiversity. The findings of the present study will help to improve knowledge and understanding of the ecological processes and mechanisms by which plankton contribute to ecosystem function in the Liujiaxia Reservoir and beyond.

Widespread distribution of the DyP-carrying bacteria involved in the aflatoxin B1 biotransformation in Proteobacteria and Actinobacteria

Aflatoxin is one of the most notorious mycotoxins, of which aflatoxin B1 (AFB1) is the most harmful and prevalent. Microbes play a crucial role in the environment for the biotransformation of AFB1. In this study, a bacterial consortium, HS-1, capable of degrading and detoxifying AFB1 was obtained. Here, we combined multi-omics and cultivation-based techniques to elucidate AFB1 biotransformation by consortium HS-1. Co-occurrence network analysis revealed that the key taxa responsible for AFB1 biotransformation in consortium HS-1 mainly belonged to the phyla Proteobacteria and Actinobacteria. Moreover, metagenomic analysis showed that diverse microorganisms, mainly belonging to the phyla Proteobacteria and Actinobacteria, carry key functional enzymes involved in the initial step of AFB1 biotransformation. Metatranscriptomic analysis indicated that Paracoccus-related bacteria were the most active in consortium HS-1. A novel bacterium, Paracoccus sp. strain XF-30, isolated from consortium HS-1, contains a novel dye-decolorization peroxidase (DyP) enzyme capable of effectively degrading AFB1. Taxonomic profiling by bioinformatics revealed that DyP, which is involved in the initial biotransformation of AFB1, is widely distributed in metagenomes from various environments, primarily taxonomically affiliated with Proteobacteria and Actinobacteria. The in-depth examination of AFB1 biotransformation in consortium HS-1 will help us to explore these crucial bioresources more sensibly and efficiently.

Difference in microbial community structure along a gradient of crater altitude: insights from the Nushan volcano

The variation in the soil microbial community along the altitude gradient has been widely documented. However, the structure and function of the microbial communities distributed along the altitude gradient in the crater still need to be determined. We gathered soil specimens from different elevations within the Nushan volcano crater to bridge this knowledge gap. We investigated the microbial communities of bacteria and fungi in the soil. It is noteworthy that the microbial alpha diversity peaks in the middle of the crater. However, network analysis shows that bacterial (nodes 760 vs 613 vs 601) and fungal (nodes 328 vs 224 vs 400) communities are most stable at the bottom and top of the crater, respectively. Furthermore, the soil microbial network exhibited a decline, followed by an increase across varying altitudes. The core microorganisms displayed the highest correlation with pH and alkaline phosphatase (AP, as determined through redundancy analysis (RDA) and Mantel tests for correlation analysis. The fungal community has a higher number of core microorganisms, while the bacterial core microorganisms demonstrate greater susceptibility to environmental factors. In conclusion, we utilized Illumina sequencing techniques to assess the disparities in the structure and function of bacteria and fungi in the soil.IMPORTANCEThese findings serve as a foundation for future investigations on microbial communities present in volcanic soil.

Soil microbial community composition and nitrogen enrichment responses to the operation of electric power substation

The surge in global energy demand mandates a significant expansion of electric power substations. Nevertheless, the ecological consequences of electric power substation operation, particularly concerning the electromagnetic field, on soil microbial communities and nitrogen enrichment remain unexplored. In this study, we collected soil samples from six distinct sites at varying distances from an electric power substation in Xintang village, southeastern China, and investigated the impacts of electromagnetic field on the microbial diversity and community structures employing metagenomic sequencing technique. Our results showed discernible dissimilarities in the fungal community across the six distinct sites, each characterized by unique magnetic and electric intensities, whereas comparable variations were not evident within bacterial communities. Correlation analysis revealed a diminished nitrogen fixation capacity at the site nearest to the substation, characterized by low moisture content, elevated pH, and robust magnetic induction intensity and electric field intensity. Conversely, heightened nitrification processes were observed at this location compared to others. These findings were substantiated by the relative abundance of key genes associated with ammonium nitrogen and nitrate nitrogen production. This study provides insights into the relationships between soil microbial communities and the enduring operation of electric power substations, thereby contributing fundamental information essential for the rigorous environmental impact assessments of these facilities.

Environmental heterogeneity caused by large-scale cultivation of Pyropia haitanensis shapes multi-group biodiversity distribution in coastal areas

The response of marine biodiversity to mariculture has long been a research focus in marine ecology. However, the effects of seaweed cultivation on biological community assembly are poorly understood, especially in diverse communities with distinct ecological characteristics. In this study, we used environmental DNA metabarcoding to investigate the spatial distribution patterns of bacterial, protistan, and metazoan diversity, aiming to reveal the mechanisms of community assembly in the Pyropia haitanensis cultivation zone along the Fujian coast, China. We found that, compared with the biological communities in control zones, those in P. haitanensis cultivation zones exhibited stronger geographic distance-decay patterns and displayed more complex and stable network structures. Deterministic processes (environmental selection) played a more important role in the assembly of bacterial, protistan, and metazoan communities in P. haitanensis cultivation zones, especially metazoan communities. Variance partitioning analysis showed that environmental variables made greater contributions to the diversity of the three types of communities within the P. haitanensis cultivation zones than in the control zones. Partial least squares path modeling analysis identified nitrate‑nitrogen (NO3-N), pH, particulate organic carbon (POC), and dissolved organic carbon (DOC) as the key environmental variables affecting biodiversity. Overall, the environmental heterogeneity caused by the large-scale cultivation of P. haitanensis could be the crucial factor influencing the composition and structure of various biological communities. Our results highlight the importance of the responses of multi-group organisms to the cultivation of seaweed, and provide insights into the coexistence patterns of biodiversity at the spatial scale.

Oxidative stress responses in biofilms

Oxidizing agents are low-molecular-weight molecules that oxidize other substances by accepting electrons from them. They include reactive oxygen species (ROS), such as superoxide anions (O2-), hydrogen peroxide (H2O2), and hydroxyl radicals (HO-), and reactive chlorine species (RCS) including sodium hypochlorite (NaOCl) and its active ingredient hypochlorous acid (HOCl), and chloramines. Bacteria encounter oxidizing agents in many different environments and from diverse sources. Among them, they can be produced endogenously by aerobic respiration or exogenously by the use of disinfectants and cleaning agents, as well as by the mammalian immune system. Furthermore, human activities like industrial effluent pollution, agricultural runoff, and environmental activities like volcanic eruptions and photosynthesis are also sources of oxidants. Despite their antimicrobial effects, bacteria have developed many mechanisms to resist the damage caused by these toxic molecules. Previous research has demonstrated that growing as a biofilm particularly enhances bacterial survival against oxidizing agents. This review aims to summarize the current knowledge on the resistance mechanisms employed by bacterial biofilms against ROS and RCS, focussing on the most important mechanisms, including the formation of biofilms in response to oxidative stressors, the biofilm matrix as a protective barrier, the importance of detoxifying enzymes, and increased protection within multi-species biofilm communities. Understanding the complexity of bacterial responses against oxidative stress will provide valuable insights for potential therapeutic interventions and biofilm control strategies in diverse bacterial species.

High levels of cadmium altered soil archaeal activity, assembly, and co-occurrence network in volcanic areas

Soil microbial communities are essential to biogeochemical cycles. However, the responses of microorganisms in volcanic soil with high heavy metal levels remain poorly understood. Here, two areas with high levels of cadmium (Cd) from the same volcano were investigated to determine their archaeal composition and assembly. In this study, the Cd concentrations (0.32-0.38 mg/ kg) in the volcanic soils exceeded the standard risk screening values (GB15618-2018) and correlated with archaeal communities strongly (P < 0.05). Moreover, the area with elevated levels of Cd (periphery) exhibited a greater diversity of archaeal species, albeit with reduced archaeal activity, compared to the area with lower levels of Cd (center). Besides, stochastic processes mainly governed the archaeal communities. Furthermore, the co-occurrence network was simplest in the periphery. The proportion of positive links between taxa increased positively with Cd concentration. Moreover, four keystone taxa (all from the family Nitrososphaeraceae) were identified from the archaeal networks. In its entirety, this study has expanded our comprehension of the variations of soil archaeal communities in volcanic areas with elevated cadmium levels and serves as a point of reference for the agricultural development of volcanic soils in China.

Comparison of Microbial Diversity of Two Typical Volcanic Soils in Wudalianchi, China

Volcanic lava is an excellent model of primary succession, in which basalt-associated microorganisms drive the cycling of different elements such as nitrogen, carbon, and other nutrients. Microbial communities in volcanic soils are of particular interest for study on the emergence and evolution of life within special and extreme conditions. The initial processes of colonization and subsequent rock weathering by microbial communities are still poorly understood. We analyzed the soil bacterial and fungal communities and diversities associated with lava (LBL) and kipuka (BK) sites in Wudalianchi using 16S and ITS rRNA Illumina Miseq sequencing techniques. The results showed that soil physical and chemical properties (pH, MC, TOC, TN, TP, AP, DOC, and DON) significantly differed between LBL and BK. The Shannon, Ace, and Pd indexes of fungi in the two sites showed a significant difference (p < 0.05). The dominant bacterial phyla forming communities at LBL and BK sites were Acidobacteria, Proteobacteria, Actinobacteria, and Basidiomycota, and their differences were driven by Gemmatimonadetes and Verrucomicrobia. The dominant fungal phyla of LBL and BK sites were Ascomycota, Zygomycota, and Rozellomcota, which differed significantly between the two sites. The microbial communities showed extremely significant differences (p < 0.05), with MC, pH, and nitrogen being the main influencing factors according to RDA/CCA and correlation analysis. Microbial functional prediction analysis across the two sites showed that the relative abundance of advantageous functional groups was significantly different (p < 0.05). The combined results drive us to conclude that the volcanic soil differences in the deposits appear to be the main factor shaping the microbial communities in Wudalianchi (WDLC) volcanic ecosystems.

Metagenomic insights into the diversity of 2,4-dichlorophenol degraders and the cooperation patterns in a bacterial consortium

2,4-Dichlorophenol, which is largely employed in herbicides and industrial production, is frequently detected in ecosystems and poses risks to human health and environmental safety. Microbial communities are thought to perform better than individual strains in the complete degradation of organic contaminants. However, the synergistic degradation mechanisms of the microbial consortia involved in 2,4-dichlorophenol degradation are still not widely understood. In this study, a bacterial consortium named DCP-2 that is capable of degrading 2,4-dichlorophenol was obtained. Metagenomic analysis, cultivation-dependent functional verification, and co-occurrence network analysis were combined to reveal the primary 2,4-dichlorophenol degraders and the cooperation patterns in the consortium DCP-2. Metagenomic analysis showed that Pseudomonas, Achromobacter, and Pigmentiphaga were the primary degraders for the complete degradation of 2,4-dichlorophenol. Thirty-nine phylogenetically diverse bacterial genera, such as Brucella, Acinetobacter, Aeromonas, Allochromatium and Bosea, were identified as keystone taxa for 2,4-dichlorophenol degradation by keystone taxa analysis of the co-occurrence networks. In addition, a stable synthetic consortium of isolates from DCP-2 was constructed, consisting of Pseudomonas sp. DD-13 and Brucella sp. FZ-1; this synthetic consortium showed superior degradation capability for 2,4-dichlorophenol in both mineral salt medium and wastewater compared with monoculture. The findings provide valuable insights into the practical bioremediation of 2,4-dichlorophenol-contaminated sites.

Effect of forest planting patterns on the formation of soil organic carbon during litter lignocellulose degradation from a microbial perspective

Litter decomposition is an important source of soil organic carbon, and it plays a key role in maintaining the stability of forest ecosystems. The microbial mechanism of soil organic carbon (SOC) formation in different urban forest planting patterns during litter lignocellulose degradation is still unclear. The key genes, microbes, and metabolites in the process of lignocellulose degradation and SOC formation were determined by metagenomics and metabolomics in different litter decomposition layers and soil layers in different urban forest planting patterns, including three types of broadleaf forests (BP forests), three types of coniferous forests (CP forests), and two types of mixed coniferous and broadleaf forests (MCBP forests). The results indicated that the cellulose, hemicellulose, and lignin concentrations from the undecomposed layer to the totally decomposed layer decreased by 70.07, 86.83, and 73.04% for CP litter; 74.30, 93.80, and 77.55% for BP litter; and 62.51, 48.58, and 90.61% for MCBP litter, respectively. The soil organic carbon of the BP forests and MCBP forests was higher than that of the CP forests by 38.06 and 94.43% for the 0-10 cm soil layer and by 38.55 and 20.87% for the 10-20 cm soil layer, respectively. Additionally, the gene abundances of glycoside hydrolases (GHs) and polysaccharide lyases (PLs) in the BP forests were higher than those in the MCBP forests and CP forests. Amino acid metabolism, sugar metabolism, TCA metabolism, and cAMP signaling metabolism were mainly between the CP forests and BP forests, while the TCA cycle, pyruvate metabolism, phenylalanine metabolism, and tyrosine metabolism were mainly between the BP forests and MCBP forests during litter decomposition. Additionally, ammonia nitrogen and hemicellulose were key factors driving SOC formation in the CP forests, while ammonia nitrogen, hemicellulose, and lignocellulose-degrading genes were key factors driving SOC formation in the BP forests. For the MCBP forests, cellulose, pH, ammonia nitrogen, and lignin were key factors driving SOC formation. Our findings revealed that the BP forests and MCBP forests had stronger lignocellulose degradation performance in the formation of SOC. This study provided a theoretical basis for the flow and transformation of nutrients in different urban forest management patterns.