Native soil organic matter as a decisive factor to determine the arbuscular mycorrhizal fungal community structure in contaminated soils

The present study of arbuscular mycorrhizal (AM) fungi is focused on the identification of AM ecotypes associated with different plants species (Poa annua, Medicago polymorpha, and Malva sylvestris) growing in three contaminated soils with different organic matter, phosphorus, and trace element (TE; Cu, Cd, Mn, and Zn) contents. Soils were amended with biosolid and alperujo compost. Shifts in AM fungal community structure, diversity, richness, root colonization, and plant TE uptake were evaluated. Soil properties and plant species had a significant effect on AM fungal community composition as well as on root colonization. However, AM fungal diversity and richness were only affected by soil properties and especially by soil organic matter that was a major driver of AM fungal community. As soil quality increased, Glomeraceae decreased in favor of Claroideoglomeraceae in the community, AM fungal diversity and richness increased, and root colonization decreased. No effect due to amendment (exogenous organic matter) addition was found either in AM fungal parameters measured or TE plant uptake. Our results revealed that the role of TE contamination was secondary for the fungal community behavior, being the native organic matter content the most significant factor.