Metal pollution-induced alterations in soil fungal community structure and functional adaptations across regional scales

Soil contamination with heavy metal(loid)s (HMs) threatens soil ecosystem health and function. However, how cross-regional HM contamination influences the structure and function of soil fungal communities remains understudied. We conducted a large-scale soil survey in southern China, using the Nemerow synthetic Pollution Index to assess contamination levels of seven metals (copper, lead, cadmium, arsenic, nickel, zinc and chromium). Soils were classified as low, medium, and high contamination (LC/MC/HC) to examine HM biogeographic patterns and their ecological impacts on soil fungi along the gradient. Cd was the most prevalent contaminant, followed by As in all the studied soils. The combined soil pollution significantly altered fungal community structure, with Cd and Pb identified as key drivers of structural and evenness changes, respectively. Fungal diversity and evenness declined with pollution, accompanied by reduced Staphylotrichum (-0.45 %) and Saitozyma (-1.5 %). Homogeneous selection dominated the assembly processes of soil fungal communities across all contamination levels (contributing 55.8–64.9 %). The most enriched characteristic species included Eurotiomycetes (LC), Sordariales (MC), and Coniochaeta (HC). Pollution-induced habitat heterogeneity enhanced the complexity and stability of fungal symbiotic networks, with 10.0 % more synergistic interactions in highly contaminated soils. The abundance of potential pathogenic fungi increased by 3.0–5.8 % in highly polluted soils compared to low- and moderately polluted soils, indicating possible negative implications for ecosystem health. Our findings provide novel and comprehensive insights into the ecological response of soil fungal communities to HM contamination.