[Characteristics and Dominant Influencing Factors of the Fungal Community Structure in Soils Co-contaminated with Rare Earth Elements and Heavy Metals].

Rare earth elements (REEs) have been listed as emerging pollutants and are often enriched together in soils with heavy metals (HMs), which results in ecological crises. The ecological effects caused by REEs have been attracting increasing amounts of attention, but most studies neglect the synergistic effect of REEs and HMs. The soil fungal community plays an important role in maintaining ecosystem functions, and understanding the fungal community structure and its dominant influencing factors in the co-contaminated soils will help to develop soil remediation strategies that could reduce or remedy the impacts of human production activities on the environment. Currently, the effects of long-term contamination of REEs and HMs on the soil fungal communities remain unclear. The Baotou rare earth tailings dam (Inner Mongolia, China) was used as the area of study, and soil samples co-contaminated with REEs and HMs were collected. Illumina high-throughput sequencing with ITS1 gene amplicons was used to analyze the fungal community diversity and structural characteristics. The results showed that the heterogeneity of soil environmental variables determined the distribution of fungal communities in a small area and constituted its own unique ecological niche in the co-contaminated environment. The fungal community richness and diversity in the co-contaminated soils were significantly lower than those in the uncontaminated soils, and the composition of the fungal community was significantly different. The results of a random forest (RF) analysis showed that TN was the most important factor that affected the fungal community richness and diversity, followed by REEs, Zn, and AK. The results of a canonical correspondence analysis (CCA) showed that Zn was the most important factor that affected the fungal community structure. A variation partitioning analysis (VPA) was performed to quantify the relative contributions of different environmental variables on the changes in fungal community structure, and the analytical results showed that all the detected environmental variables could explain 93.3% of the variation in soil fungal community. The combined effect of soil physicochemical properties and pollution factors (REEs and HMs) accounted for 58.5% of the total variation, and their contribution alone accounted for 13.5% and 21%, respectively. The effects of these pollution factors on the fungal communities were slightly higher than those of the soil physicochemical properties. The synergistic contributions of REEs and HMs were 40.1%, and their individual effects were 21.8% and 17.9%, respectively. Therefore, the soil physicochemical properties, REEs, and HMs regulated the fungal community structure and composition in concert. The synergistic contributions of REEs and HMs were greater than their individual effects, and these results suggest that it is necessary to further strengthen the risk control of the co-contamination of REEs and HMs in the soil environment.