Effect of AM Fungi Inoculation on Litter Bacterial Community Characteristics under Heavy Metal Stress

Functional insights into microbial community dynamics and resilience in mycorrhizal associated constructed wetlands under pesticide stress

Arbuscular mycorrhizal fungi (AMF) are critical mutualistic symbionts in most terrestrial ecosystems, where they facilitate nutrient acquisition, enhance plant resilience to environmental stressors, and shape the surrounding microbiome. However, its contributions (especially for microorganisms) to constructed wetlands (CWs) under pesticide stress remain poorly understood. This study investigated the effects of AMF on microbial community composition, diversity, metabolic pathways, and functional genes by metagenomics in CWs exposed to pesticides stress. Using comparative analyses of AMF-colonized and non-colonized CWs, we found that AMF enhanced overall microbial diversity, as evidenced by increases of 2.22 % (Chao1) and 2.83 % (observed species). Under fungicide stress, nitrogen-cycling microorganisms (e.g., Nitrososphaerota and Mucoromycota) increased in relative abundance, while carbon cycle-related microorganisms (e.g., Pseudomonadota and Bacteroidota) generally declined. AMF colonization improved microbial resilience, demonstrated by a 312 % rise in Rhizophagus abundance and significant increases in phosphorus-cycling microorganisms (e.g., Bradyrhizobium and Mesorhizobium). Functional gene analysis further revealed that AMF helped mitigate fungicide-induced reductions in genes related to nitrogen and carbon cycling, lowering the average decline rates to 4.02 % and 1.44 %, respectively, compared to higher rates in non-AMF treatments. In summary, these findings highlight the crucial role of AMF in enhancing pesticide stress resilience, maintaining microbial community stability, and improving the bioremediation capacity of CWs.

Changes in rainfall impact the release of metal elements in the litter of a subtropical mixed forest

The release of metal elements from litter decomposition in forest ecosystems is crucial for material cycling and ecosystem health, but the impact of future variations in rainfall due to climatic fluctuations on this release is unknown. This study conducted an outdoor rainfall variability simulation and an in situ litter decomposition experiment in a subtropical location, with a focus on pure Pinus massoniana (PM) and 4 p.m. mixed stands (PM+Bretschneidera sinensis, PM+Cercidiphyllum japonicum, PM+Taxus wallichiana, and PM+Nageia nagi). We studied the release of metal elements from litter after one year of decomposition under different rainfall conditions (30% increase, natural, and 30% decrease) and calculated the mixing effect on the litter. The results showed that K, Mg, Mn, Cu and Zn were released and Na, Ca and Fe were enriched after one year of litter decomposition. Increased rainfall promoted K, Na, Mg, Mn, and Zn release, reduced Fe and Cu release, enhanced the synergistic effect of Na and Mn release, and exacerbated the antagonistic effect of Cu. Decreased rainfall reduced the synergistic effect of mixed litter on the release of Na, Ca, Mg, and Fe, while enhancing the synergistic effect of Mn and Zn. The lower degree of metal element release from single PM litter resulted in the enrichment of metal elements in the litter of apoplasts. The effect of rainfall variability on metal element release was more significant compared to tree species characteristics. Overall, decreased rainfall inhibited metal element release and slowed down element cycling; increased rainfall promoted Na and Mn release and accelerated Cu enrichment. It is noteworthy that mixed litter effectively mitigated the effects of rainfall changes on metal element release by regulating elemental cycling. The findings of this study add to a better understanding of nutrient dynamics in forest ecosystems and offer techniques and insights for addressing future climate change.

The invasion of Cassytha filiformis accelerated the litter decomposition of native plant communities in small tropical coral islands

BACKGROUND

Plant invasion affects plant community composition, biodiversity, and nutrient cycling in terrestrial ecosystems, particularly in vulnerable ecosystems. As an invasive parasitic plant, Cassytha filiformis has caused extensive damage to the native vegetation of the Paracel Islands. However, the effects of C. filiformis invasion on litter decomposition and nutrient release in native plant communities remain unclear. We conducted an in-situ decomposition experiment in native plant communities on a coral island to explore the litter decomposition dynamics varying across enzyme activities, soil properties and C. filiformis invasive degrees.

RESULTS

The mass loss of litter was determined during the decomposition process. The data showed that litter mass loss under severe invasion was significantly lower than in uninvaded sites after nine months of decomposition. The invasion of C. filiformis accelerated the nitrogen release and lignin decomposition with increased litter quality and polyphenol oxidase activity. Besides, soil phosphorus availability and potassium content also induced the oxidase activity. Meanwhile, the decomposition of litter organic carbon was delayed because β-1, 4-glucosidase activity was low in the first six months. Besides, peroxidase activity maintained a high level in invasive plots, indicating that the residues of C. filiformis may have allelopathy.

CONCLUSION

Our results suggested that the invasion of C. filiformis accelerated litter mass loss and element release on coral islands by regulating litter quality and enzyme activity. However, the short-term rapid litter decomposition may result in nutrient loss, which is not conducive to the growth of native plants.

The Ecological Restoration Strategies in Terrestrial Ecosystems Were Reviewed: A New Trend Based on Soil Microbiomics

Soil microorganisms play a pivotal role in the biogeochemical cycle and serve as crucial indicators of ecological restoration in terrestrial ecosystems. The soil microbial community is regarded as a pivotal participant in environmental processes, offering both positive and negative feedback to diverse media within the ecosystem. This community can serve as a potential indicator in ecological monitoring and restoration processes. Consequently, an increasing number of scholars are directing their research towards the field of soil microbial ecology in diverse ecosystems and fragile areas, with the aim of elucidating the intricate interactions between microbes and vegetation. However, the implementation of soil microbiome in ecological restoration remains in the experimental stage due to the interference of extreme events and the complexity of governance measures. Consequently, a comprehensive evaluation of existing research is imperative. This review aims to address the ecological crises currently experienced by diverse terrestrial ecosystems and to provide a comprehensive overview of the specific practices of soil microorganisms in the context of ecological restoration. We also incorporate them into fragile habitats and identify urgent issues that need to be addressed in the ecological restoration process of fragile areas.

Critical steps in the restoration of coal mine soils: Microbial-accelerated soil reconstruction

Soil reconstruction is a critical step in the restoration of environments affected by mining activities. This paper provides a comprehensive review of the significant role that microbial processes play in expediting soil structure formation, particularly within the context of mining environment restoration. Coal gangue and flotation tailings, despite their low carbon content and large production volumes, present potential substrates for soil reclamation. These coal-based solid waste materials can be utilized as substrates to produce high-quality soil and serve as an essential carbon source to enhance poor soil conditions. However, extracting active organic carbon components from coal-based solid waste presents a significant challenge due to its complex mineral composition. This article offers a thorough review of the soilization process of coal-based solid waste under the influence of microorganisms. It begins by briefly introducing the primary role of in situ microbial remediation technology in the soilization process. It then elaborates on various improvements to soil structure under the influence of microorganisms, including the enhancement of soil aggregate structure and soil nutrients. The article concludes with future recommendations aimed at improving the efficiency of soil reconstruction and restoration, reducing environmental risks, and promoting its application in complex environments. This will provide both theoretical and practical support for more effective environmental restoration strategies.

Community ecological study on the reduction of soil antimony bioavailability by SRB-based remediation technologies

Sulfate-reducing bacteria (SRB) were effective in stabilizing Sb. However, the influence of electron donors and acceptors during SRB remediation, as well as the ecological principles involved, remained unclear. In this study, Desulfovibrio desulfuricans ATCC 7757 was utilized to stabilize soil Sb within microcosm. Humic acid (HA) or sodium sulfate (Na2SO4) were employed to enhance SRB capacity. The SRB+HA treatment exhibited the highest Sb stabilization rate, achieving 58.40%. Bacterial community analysis revealed that SRB altered soil bacterial diversity, community composition, and assembly processes, with homogeneous selection as the predominant assembly processes. When HA and Na2SO4 significantly modified the stimulated microbial community succession trajectories, shaped the taxonomic composition and interactions of the bacterial community, they showed converse effect in shaping bacterial community which were both helpful for promoting dissimilatory sulfate reduction. Na2SO4 facilitated SRB-mediated anaerobic reduction and promoted interactions between SRB and bacteria involved in nitrogen and sulfur cycling. The HA stimulated electron generation and storage, and enhanced the interactions between SRB and bacteria possessing heavy metal tolerance or carbohydrate degradation capabilities.

Fungal community characteristics and driving factors in Bothriochloa ischaemum litter in a copper mining area

Among influencing biotic and abiotic factors, microorganisms predominate litter decomposition, playing an important role in maintaining the ecosystem material cycle. Bothriochloa ischaemum was the dominant plant species in China's Eighteen River tailings dam, and it was selected as the research object. We explored the dynamic of fungal community characteristics in B. ischaemum litter during different decomposition stages and investigated relevant driving factors affecting associative dynamic changes. Results showed that Ascomycetes and Basidiomycetes were the dominant phyla during litter decomposition. At a class level, the relative abundance of Dothideomycetes gradually decreased as litter decomposition progressed while Sordariomycetes gradually increased, ultimately becoming the dominant class. The community structure of the fungal community was mainly affected by litter pH, total carbon (TC), and copper (Cu) content. The fungal community's network structure was the most complex compared to other decomposition stages after 200 days of litter decomposition. Additionally, the fungal community's modularity gradually increased, while the degree of functional differentiation also increased, strengthening fungal community stability during litter decomposition. This study clarifies fungal community structure during litter decomposition in this copper tailings area, and provides a scientific basis for further improving soil fertility and nutrient cycling in mining areas.

Long-term comparison of the performance of biostimulation and phytoextraction in soil contaminated with diesel and heavy metals

The long-term remediation performance under the natural conditions is required to establish the appropriate remediation strategy for contaminated soil. The objective of this study was to compare the long-term remediation efficiency of biostimulation and phytoextraction in contaminated soil containing petroleum hydrocarbons (PHs) and heavy metals. Two types of contaminated soil (soil contaminated with diesel only and co-contaminated with diesel and heavy metals) were prepared. For the biostimulation treatments, the soil was amended with compost, whereas maize, a representative phytoremediation plant, was cultivated for the phytoextraction treatments. There was no significant difference in remediation performance of biostimulation and phytoextraction in the diesel-contaminated soil, in which the maximum total petroleum hydrocarbon (TPH) removability was 94-96% (p < 0.05). However, phytoextraction exhibited the higher removability for TPH and heavy metals than biostimulation in the co-contaminated soil. There was no considerable change in the TPH removal in biostimulation (16-25%), while phytoextraction showed a 75% of TPH removal rate in the co-contaminated soil. Additionally, no significant changes were observed in heavy metals concentration of biostimulation, whereas the removability of heavy metals was 33-63% in phytoextraction. Meanwhile, maize, which is a suitable plant for phytoextraction, showed a translocation factor (translocating efficiency from roots to shoots) value of >1. Correlation analysis revealed that soil properties (pH, water content, and organic content) negatively correlated with pollutants removal. Additionally, the soil bacterial communities were changed over the investigated period, and the types of pollutants exerted a significant influence on the bacterial community dynamics. This study performed a pilot-scale comparison of two types of biological remediation technologies under natural environmental conditions and provided information on changes in the bacterial community structures. This study can be useful for establishing appropriate biological remediation methods to restore soil contaminated with PHs and heavy metals.

Effects of AMF inoculation on the eco-physiological characteristics of Imperata cylindrica under differing soil nitrogen conditions

Arbuscular mycorrhizal fungi (AMF) play a key role in terrestrial ecosystems, while the ecological restoration application of AMF in mining areas has been progressively gaining attention. This study simulated a low nitrogen (N) environment in copper tailings mining soil to explore inoculative effects of four AMF species on the eco-physiological characteristics of Imperata cylindrica, and provided plant-microbial symbiote with excellent resistance to copper tailings. Results show that N, soil type, AMF species, and associated interactions significantly affected ammonium (NH4  +), nitrate nitrogen (NO3  -), and total nitrogen (TN) content and photosynthetic characteristics of I. cylindrica. Additionally, interactions between soil type and AMF species significantly affected the biomass, plant height, and tiller number of I. cylindrica. Rhizophagus irregularis and Glomus claroideun significantly increased TN and NH4  + content in the belowground components I. cylindrica in non-mineralized sand. Moreover, the inoculation of these two fungi species significantly increased belowground NH4  + content in mineralized sand. The net photosynthetic rate positively correlated to aboveground total carbon (TC) and TN content under the high N and non-mineralized sand treatment. Moreover, Glomus claroideun and Glomus etunicatum inoculation significantly increased both net photosynthetic and water utilization rates, while F. mosseae inoculation significantly increased the transpiration rate under the low N treatment. Additionally, aboveground total sulfur (TS) content positively correlated to the intercellular carbon dioxide (CO₂) concentration, stomatal conductance, and the transpiration rate under the low N sand treatment. Furthermore, G. claroideun, G. etunicatum, and F. mosseae inoculation significantly increased aboveground NH4  + and belowground TC content of I. cylindrica, while G. etunicatum significantly increased belowground NH4  + content. Average membership function values of all physiological and ecological I. cylindrica indexes infected with AMF species were higher compared to the control group, while corresponding values of I. cylindrica inoculated with G. claroideun were highest overall. Finally, comprehensive evaluation coefficients were highest under both the low N and high N mineralized sand treatments. This study provides information on microbial resources and plant-microbe symbionts in a copper tailings area, while aiming to improve current nutrient-poor soil conditions and ecological restoration efficiency in copper tailings areas.

The mechanism of promoting rhizosphere nutrient turnover for arbuscular mycorrhizal fungi attributes to recruited functional bacterial assembly

Symbiosis with arbuscular mycorrhizal (AM) fungi improves plant nutrient capture from the soil, yet there is limited knowledge about the diversity, structure, functioning, and assembly processes of AM fungi-related microbial communities. Here, 16S rRNA gene sequencing and metagenomic sequencing were used to detect bacteria in the rhizosphere of Lotus japonicus inoculated with and without AM fungi, and the L. japonicus mutant ljcbx (defective in symbiosis) inoculated with AM fungi in southern grassland soil. Our results show that AM symbiosis significantly increased bacterial diversity and promoted deterministic processes of bacterial community construction, suggesting that mycorrhizal symbiosis resulted in the directional enrichment of bacterial communities. AM fungi promoted the enrichment of nine bacteria, including Ohtaekwangia, Niastella, Gemmatimonas, Devosia, Sphingomonas, Novosphingobium, Opitutus, Lysobacter, Brevundimonas, which are positively correlated with NPK-related parameters. Through a functional identification experiment, we found that six of these genera, including Brevundimonas, Lysobacter, Ohtaekwangia, Sphingomonas, Devosia, and Gemmatimonas, demonstrated the ability to mineralize organophosphate and dissolve inorganic phosphorus, nitrogen, and potassium. Our study revealed that AM fungi can regulate rhizosphere bacterial community assembly and attract specific rhizosphere bacteria to promote soil nutrient turnover in southern grasslands.

Rhizosphere Microbial Communities and Geochemical Constraining Mechanism of Antimony Mine Waste-Adapted Plants in Southwestern China

Antimony (Sb) and arsenic (As) are two hazardous metalloid elements, and the biogeochemical cycle of Sb and As can be better understood by studying plant rhizosphere microorganisms associated with Sb mine waste. In the current study, samples of three types of mine waste—Sb mine tailing, waste rocks, and smelting slag—and associated rhizosphere microorganisms of adapted plants were collected from Qinglong Sb mine, southwest China. 16S rRNA was sequenced and used to study the composition of the mine waste microbial community. The most abundant phylum in all samples was Proteobacteria, followed by Bacteroidota, Acidobacteriota, and Actinobacteriota. The community composition varied among different mine waste types. Gammaproteobacteria was the most abundant microorganism in tailings, Actinobacteria was mainly distributed in waste rock, and Saccharimonadia, Acidobacteriae, and Ktedonobacteria were mainly present in slag. At the family level, the vast majority of Hydrogenophilaceae were found in tailings, Ktedonobacteraceae, Chthoniobacteraceae, and Acidobacteriaceae (Subgroup 1) were mostly found in slag, and Pseudomonadaceae and Micrococcaceae were mainly found in waste rock. Actinobacteriota and Arthrobacter are important taxa for reducing heavy metal(loid) mobility, vegetation restoration, and self-sustaining ecosystem construction on antimony mine waste. The high concentrations of Sb and As reduce microbial diversity.