Indigenous inoculant dampens the impact of remediation of heavy metal polluted soil on arbuscular mycorrhizal fungal communities

The finite resource of fertile soil can take thousands of years to develop. Non-degradable toxic metals (heavy metals), pose a significant health risk due to their persistence in the environment. Soil washing with EDTA (ethylenediaminetetraacetic acid) has been shown to remove toxic metals (Pb, Zn, Cd), but this process can also have a significant impact on soil microbial diversity. In this study, we investigated, using molecular methods (18S rRNA amplicon sequencing), the development of the arbuscular mycorrhizal (AM) fungal communities in the roots of Lolium perenne after a soil remediation treatment with EDTA. Plants were grown on two soil types (calcareous and acidic), in remediated and control (unremediated, polluted) soils, and with or without the addition of a local environmental inoculant (grassland soil and roots). The addition of the inoculant increased the richness and evenness of AM fungi, and reduced the compositional dissimilarity of communities between remediated and unremediated soils. Disturbance from the remediation process and inoculation, lead to a shift in the identity of dominant taxa reflecting different traits among the AM fungi. This suggested two main mechanisms behind community development in remediated soils, i.e. priority effects and competitive exclusion among dominant taxa. These findings emphasise the importance of nature-based solutions (indigenous environmental inoculants) and AM fungi for sustainable soil management practices. This is particularly important for restoring soil biodiversity in sites that have been exposed to multiple disturbances, which may include contaminated sites and soil remediation, as well as conventional agricultural systems, and urban soils.