Differential effects of tree species identity on rhizospheric bacterial and fungal community richness and composition across multiple trace element-contaminated sites

Soil polluted system shapes endophytic fungi communities associated with Arundo donax: a field experiment

With the expansion of the mining industry, environmental pollution from microelements (MP) and red mud (RM) has become a pressing issue. While bioremediation offers a cost-effective and sustainable solution, plant growth in these polluted environments remains difficult. Arundo donax is one of the few plants capable of surviving in RM-affected soils. To identify endophytic fungi that support A. donax in different contaminated environments and to inform future research combining mycorrhizal techniques with hyperaccumulator plants, we conducted a field experiment. The study compared endophytic fungal communities in A. donax grown in uncontaminated, MP soils contaminated with cadmium (Cd), arsenic (As), and lead (Pb), and RM-contaminated soils. Our findings showed that soil nutrient profiles differed by contamination type, with Cd concentrations in MP soils exceeding national pollution standards (GB 15168-2018) and RM soils characterized by high aluminum (Al), iron (Fe), and alkalinity. There were significant differences in the endophytic fungal community structures across the three soil types (p < 0.001). Co-occurrence network analysis revealed that endophytic fungi in MP soils exhibited competitive niche dynamics, whereas fungi in RM soils tended to share niches. Notably, Pleosporales sp., which accounted for 18% of the relative abundance in RM soils, was identified as a dominant and beneficial endophyte, making it a promising candidate for future bioremediation efforts. This study provides valuable insights into the role of endophytic fungi in phytoremediation and highlights their potential as resources for improving plant-microbe interactions in contaminated environments.

Biochar and organic fertilizer drive the bacterial community to improve the productivity and quality of Sophora tonkinensis in cadmium-contaminated soil

Excessive Cd accumulation in soil reduces the production of numerous plants, such as Sophora tonkinensis Gagnep., which is an important and widely cultivated medicinal plant whose roots and rhizomes are used in traditional Chinese medicine. Applying a mixture of biochar and organic fertilizers improved the overall health of the Cd-contaminated soil and increased the yield and quality of Sophora. However, the underlying mechanism between this mixed fertilization and the improvement of the yield and quality of Sophora remains uncovered. This study investigated the effect of biochar and organic fertilizer application (BO, biochar to organic fertilizer ratio of 1:2) on the growth of Sophora cultivated in Cd-contaminated soil. BO significantly reduced the total Cd content (TCd) in the Sophora rhizosphere soil and increased the soil water content, overall soil nutrient levels, and enzyme activities in the soil. Additionally, the α diversity of the soil bacterial community had been significantly improved after BO treatment. Soil pH, total Cd content, total carbon content, and dissolved organic carbon were the main reasons for the fluctuation of the bacterial dominant species. Further investigation demonstrated that the abundance of variable microorganisms, including Acidobacteria, Proteobacteria, Bacteroidetes, Firmicutes, Chloroflexi, Gemmatimonadetes, Patescibacteria, Armatimonadetes, Subgroups_ 6, Bacillus and Bacillus_ Acidiceler, was also significantly changed in Cd-contaminated soil. All these alterations could contribute to the reduction of the Cd content and, thus, the increase of the biomass and the content of the main secondary metabolites (matrine and oxymatrine) in Sophora. Our research demonstrated that the co-application of biochar and organic fertilizer has the potential to enhance soil health and increase the productivity and quality of plants by regulating the microorganisms in Cd-contaminated soil.