Drivers and adaptive strategies of DSE colonization in reed roots in Baiyang Lake under heavy metal stress.

Global industrial pollution and agricultural expansion pose severe challenges, such as heavy metal contamination, necessitating sustainable remediation. Dark septate endophytes (DSE) are a group of root-colonizing fungi, some members of which have been reported to tolerate environmental stress and influence host plant performance. This study focused on reeds (Phragmites australis) and their rhizosphere soil in Baiyang Lake, China. Across four sampling sites-sewage discharge areas, farmland areas, abandoned parking areas, and urban residential areas-with varying degrees of heavy metal pollution, soil physicochemical properties were measured, rhizosphere microbial community structure was characterized using amplicon sequencing, and DSE root colonization was quantified through root staining and microscopic examination. The resulting data were used to explore the relationships of DSE colonization rates with soil physicochemical properties and rhizosphere microbial communities. Microscopic colonization analysis of stained root segments revealed widespread DSE colonization in reed roots, with the highest total colonization rate (66.7%) recorded at the sewage discharge site (SA), which exhibited the most severe heavy metal contamination. After BH-FDR correction, hyphae colonization and total DSE colonization rates were positively associated with soil moisture and Pb concentration, but negatively associated with soil pH, total nitrogen, Cr concentration, and the relative abundance of Proteobacteria (q < 0.05). Microscopic analysis further showed that hyphal colonization varied more widely among sites (21.2-63.3%) than microsclerotial colonization (22.2-35.6%), indicating site-specific variation in hyphal and microsclerotial colonization patterns. This study provides insights into DSE colonization behavior under contrasting heavy metal stress conditions and supports further investigation into whether plants recruit or maintain DSE in metal-contaminated environments.