Research Progress and Potential Functions of AMF and GRSP in the Ecological Remediation of Metal Tailings

Mycorrhizal extraradical mycelium can reduce cadmium uptake by maize and cadmium leaching from contaminated soil: based on an in-growth core experiment

Arbuscular mycorrhizal fungi (AMF) are commonly found in heavy metal-contaminated environments and form extraradical mycelium (ERM), but knowledge of their ecological functions is limited. In the present study, a soil column was filled with sterilized cadmium (Cd)-contaminated soil and contained an in-growth core for AMF-inoculated maize seedling growth. The in-growth core was static to maintain or rotated to disrupt ERM growth. Compared with the static treatment, the rotation treatment caused significant decreases in the content of glomalin-related soil protein (GRSP), the photosynthetic physiology of leaves, and maize growth, while increasing the Cd content in shoots and roots by 64 and 82%, respectively; additionally, the rotation treatment resulted in increases in the Cd concentration of the soil solution inside and outside the growth core by 30-38 and 17-52%, respectively, and Cd leaching loss by 29-39%. Moreover, the rotation treatment significantly altered the Cd forms in the soil solution and leachate, increasing the proportion of free Cd2+ by 0.8-2.1% and decreasing the proportions of CdSO4(aq) and CdOH+ by 6.1-56.1% and 26.1-48.7%, respectively. The structural equation model indicated that AMF directly and indirectly reduced maize Cd uptake and Cd leaching loss by decreasing Cd availability in the soil and soil solution through the GRSP secreted by ERM. Thus, AMF plays a crucial role in inhibiting Cd migration in soil through mycelial exudates.

Microbial-mediated metal(loid) immobilization in mulch-covered tailings

Mulch coverage of mining tailings can create anaerobic conditions and consequently establish an anoxic environment that promotes the metabolic processes of anaerobic microorganisms. This anoxic environment has the potential to decrease heavy metal mobility and bioavailability. While tailings exposed to sunlight have been extensively studied, research on the effects of microbial-mediated geochemical cycling of heavy metals in mulch-covered tailings is scarce. This study aimed to examine the effects of mulch coverage-induced alterations in the structures of tailing microbial communities on the biogeochemical processes associated with heavy metals. Mulch coverage significantly reduced the pH of the tailings and the tailings exhibited heavy metal bioavailability. Random forest analysis demonstrated that mulch coverage-induced changes in the As/Cd-contaminated fractions and nutrients (total organic carbon and total nitrogen) were the most crucial predictors of microbial diversity and ecological clusters in the tailings. Notably, different from direct metal(loid) immobilization, mulch coverage can facilitate heavy metal immobilization in tailings by promoting microbial-mediated Fe, S, and As reduction. Overall, this study demonstrated that mulch coverage of tailings contributed to a reduction in heavy metal mobilization, which can be attributed to shifts in microbial-mediated Fe, S, and As reduction processes.The study provides valuable insights into the potential of mulch coverage as a remediation strategy and underscores the importance of microbial-mediated processes in managing heavy metal pollution in tailing systems.

Habitat ecological characteristics and soil fungal community structure of Paphiopedilum subgenus Brachypetalum Hallier (Orchidaceae) plants in Southwest China

Species of the subgenus Brachypetalum are the most primitive, most ornamental and most threatened group in the Orchid. This study revealed the ecological characteristics, soil nutrient characteristics and soil fungal community structure of habitats of the subgenus Brachypetalum in Southwest China. Lays a foundation for research on the wild populations and conservation Brachypetalum. The results showed that species of the subgenus Brachypetalum preferred a cool and humid environment, grew in scattered or aggregated form in narrow negative terrain, mainly in humic soil. The soil physical and chemical properties and soil enzyme activity indexes of the habitats were significantly different among different species, and the soil properties of different distribution points of the same species also varied greatly. There were significant differences in the soil fungal community structure among the habitats of different species. Basidiomycetes and ascomycetes were the main fungi in habitats of subgenus Brachypetalum species, and their relative abundance varied among different species. The functional groups of soil fungi were mainly symbiotic fungi and saprophytic fungi. LEfSe analysis found that there were different numbers and species of biomarkers in the habitats of subgenus Brachypetalum species, indicating that the habitat preference characteristics of each species in subgenus Brachypetalum were reflected in the fungal community. It was found that environmental factors had an impact on the changes in soil fungal communities in the habitats of subgenus Brachypetalum species, with climatic factors having the highest explanation rate (20.96%). Soil properties were significantly positively or negatively correlated with a variety of dominant soil fungal groups. Conclusions: The results of this study lay the foundation for the study of the habitat characteristics of wild populations of subgenus Brachypetalum and provides data to support in situ and ex situ conservation in the future.