Long-term in situ dynamics of the fungal communities in a multi-contaminated soil are mainly driven by plants

The fungal communities of a multi-contaminated soil polluted by polycyclic aromatic hydrocarbons and heavy metals (NM) were studied within a long-term in situ experiment of natural attenuation assisted by plants. Three treatments were monitored: bare soil (NM-BS), soil planted with alfalfa and inoculated with mycorrhizal fungi (NM-Msm), and soil with spontaneous vegetation (NM-SV). The same soil after thermal desorption (TD) was planted with alfalfa and inoculated with mycorrhizal fungi (TD-Msm). Twice a year for 5 years, the fungal abundance and the community structure were evaluated by real-time PCR and temporal temperature gradient gel electrophoresis targeting 18S rRNA genes. The fungal abundance increased over time and was higher in planted than in bare NM soil and in TD than in NM soil. The Shannon diversity index (H') increased during the first 2 years with the emergence of more than 30 ribotypes, but decreased after 3 years with the selection of a few competitive species, mostly Ascomycetes. H' was higher under complex plant assemblage (NM-SV) than in the NM-BS plots but did not differ between NM and TD soils planted with alfalfa. These results indicated that even in a highly polluted soil, the plant cover was the main driver of the fungal community structure.