Bacterial community characteristics and enzyme activities in Imperata cylindrica litter as phytoremediation progresses in a copper tailings dam

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.

Grafting with an invasive Xanthium strumarium improves tolerance and phytoremediation of native congener X. sibiricum to cadmium/copper/nickel tailings

Invasive plants could play an important role in the restoration of tailings, but their invasiveness limits their practical application. In this study, the phytoremediation potentials and invasive risks of an exotic invasive plant (Xanthium strumarium, LT), a native plant (X. sibiricum, CR), and combinations of inoculations (EG, with CR as the scion and LT as the rootstock; SG, with CR as both the scion and rootstock) were evaluated on Cd/Cu/Ni tailings. LT rootstock has a stronger nutrient and metal transport capacity, compared with CR. EG not only had higher biomass and Cd/Cu/Ni accumulation, but also abundant rhizosphere microbial communities. Hydroponic and common garden experiments showed that the growth and metal enrichment characteristics of EG are not inherited by plant offspring, which reduces the risk of the biological diffusion in the process of using exotic species. Transcriptome analysis shows that a large number of differentially-expressed genes in EG leaves and roots are involved in phenylpropanoid biosynthesis, secondary metabolite generation, and signal transduction. The genes induced in EG leaves, including cyclic nucleotide-gated ion channel, calcium-binding protein, and WRKY transcription factor, were found to be differentially expressed compared to CR. The genes induced in EG roots, included phenylalanine ammonia-lyase, cinnamoyl-CoA reductase, caffeoyl-CoA O-methyltransferase, and beta-glucosidase. We speculate that lignin and glucosinolates play an important role in the metal accumulation and transportation of EG. The results demonstrate that grafting with LT not only improved CR tolerance and accumulation of Cd, Cu, and Ni, but also created a beneficial microbial environment for plants in tailings. More importantly, grafting with LT did not enhance the invasiveness of CR. Our results provide an example of the safe use of invasive plants in the restoration of Cd/Cu/Ni tailings.

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

Because microorganisms are the primary driving force behind litter decomposition, they play an important role in maintaining ecosystem material and chemical cycling. Arbuscular mycorrhizal (AM) fungi can improve host plant tolerance to various environmental stressors, making their application in mining area remediation important. In this study, litter from the dominant plant species (Imperata cylindrica) in a copper tailings mining area was selected as the experimental material. We conducted a greenhouse-based heavy metal stress experiment to investigate how AM fungi affect litter microbial community characteristics and key ecological factors. Results showed that AM fungi species, heavy metal treatments, and their combined interaction had significant impacts on litter pH. Additionally, enzyme activities in litter were significantly affected by interactions between AM fungi species and heavy metal contaminates. Ralstonia was significantly positively correlated to lead (Pb) content, indicating that Ralstonia had a certain tolerance to Pb pollution. Sucrase and urease activity were increased when plants were inoculated with Rhizophagus irregularis under Pb stress. Furthermore, Microbacterium, Brevundimonas, and Pseudonocardia all may play important roles in litter decomposition, while a certain tolerance was observed in Kushneria and Roseivivax to heavy metal pollution when plants were inoculated with Glomus mosseae. Results showed that AM fungi affected litter bacterial community structure and function by influencing plant litter properties. By exploring interactions between AM fungi and bacterial communities in plant litter under heavy metal stress, we will better understand associative processes that promote the cycling of soil organic matter and nutrients contaminated by non-ferrous metal tailings.