Impact of repeated irrigation of lettuce cultures with municipal wastewater on the diversity and composition of root-associated arbuscular mycorrhizal fungi

In previous two-tier experiments designed to test agronomical (treated wastewater) and worst-case scenario (wastewater spiked with a mixture of 14 pharmaceuticals and personal care products (PPCPs) at 10 and 100 μg/L), 14 different wastewater-borne PPCPs accumulated in soil, lettuce roots, and leaves leading to a significant ecotoxicological impact on soil and root-associated bacteria. Here, we assessed the effects of wastewater irrigation on the arbuscular mycorrhizal fungal (AMF) colonization, diversity, and composition in lettuce roots. Neither the wastewater nor the concentration of spiked PPCPs had an impact on the colonization, alpha-diversity indices (Chao1, PD whole tree, Simpson reciprocal, and Shannon), and composition of root-associated AMF communities. Taxonomical analysis of the fungi revealed the presence of 14 major phylotypes, 13 of which belonged to the Glomeromycota division. As for the alpha and beta diversity indices, none of the phylotypes was affected by either the wastewater or the PPCPs. This indicates that under both agronomical and worst-case scenario, the irrigation of lettuce with wastewater had no effect on the root-associated AMF community.