稀土-重金属共污染土壤中真菌群落结构特征及主导影响因素

稀土元素已被列为新兴污染物,稀土元素经常与重金属在土壤中富集,造成生态危机.稀土污染的生态效应已逐渐受到关注,但忽视了稀土与重金属共存的协同效应.了解稀土和重金属共污染土壤中真菌群落结构及主导影响因素,有助于制定土壤修复策略,以减少或补救人类生产活动对环境的影响.目前,长期稀土和重金属污染对土壤真菌群落的影响尚不清楚.以包头稀土尾矿坝为研究区域,利用ITS1基因扩增子Illumina高通量测序分析稀土和重金属共污染土壤中真菌群落多样性和结构特征.结果表明,在共污染环境中,土壤环境变量的异质性决定了真菌群落在小范围内的分布,构成独特的生态位.污染土壤的真菌群落丰富度和多样性显著低于未污染土壤,且真菌群落组成差异明显.随机森林分析结果表明,TN是影响真菌群落丰富度和多样性的最主要因素,其次是稀土元素、重金属Zn和AK.CCA分析结果表明,重金属Zn是影响真菌群落结构的最关键因素.VPA分析结果显示,所检测环境变量能够解释土壤真菌群落变化93.3%的差异,土壤理化性质与污染因子（稀土和重金属）的综合效应解释了总差异的58.5%,二者单独解释的贡献度分别为13.5%和21%,污染因子的贡献度稍高于土壤理化性质;稀土和重金属的协同效应对总差异的贡献度为40.1%,各自的单独作用分别为21.8%和17.9%.因此,共污染环境中真菌群落结构和组成受土壤理化性质、稀土和重金属的共同调控,稀土和重金属的协同效应大于各自的单独作用,研究结果表明需要进一步加强土壤环境中稀土元素和重金属共污染的风险管控.

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.