Effects of biological and abiotic factors on dark septate endophytes distribution and heavy metal resistance in different environments.

Introduction: Exploring the interactions between dark septate endophytes (DSE) in plant roots across diverse heavy metal habitats-considering host plants, site characteristics, and microbial communities-provides insights into the distribution patterns of DSE in metal-rich environments and their mechanisms for developing heavy metal resistance.

Methods: This study collected samples of three common plant species (, PA, , SV, and , AA) and their corresponding soil samples from three heavy metal-contaminated sites: Baiyang Lake, BY, Fengfeng mining area, FF, and Huangdao, HD. Utilizing high-throughput sequencing and physicochemical analysis methods, the biological and abiotic factors affecting DSE colonization and distribution in the roots were investigated.

Results: Twenty-two DSE species were isolated and identified with 11 species found in BY, 8 species in FF, and 11 species in HD. The screening for heavy metal resistance discovered 10 heavy metal-tolerant DSE species. Soil available phosphate, available nitrogen, and Cd contents, as well as the composition of different root fungal communities, influence the resistance and distribution of heavy metal-tolerant DSE. Notably, 12 DSE species, including and , were reported for the first time in heavy metal habitats. The colonization rates of DSE in the roots of PA (96%) and AA (76%) were highest in BY, while the highest colonization rate in the roots of SV was observed in HD (94%). Site-specific soil parameters, such as available K, organic contents, Zn, and Cd contents from different sites are the main determinants affecting DSE colonization. Meanwhile, the diversity and richness of other root-associated endophytic fungi, which varied considerably across sites, served as significant biological factors influencing DSE distribution and colonization.

Discussion: The results of this study provide a strong theoretical framework for the effective utilization of DSE fungi to mitigate soil heavy metal pollution.