25S rDNA-based molecular monitoring of glomalean fungi in sewage sludge-treated field plots

Recycling of sewage wastes in agriculture is likely to affect the biologica l activity of soils through contamination of ecosystems by pathogens and me tallic or organic micropollutants. The impact of sewage sludge spreading un der field conditions on arbuscular mycorrhiza (AM) formation by a community of glomalean fungi was evaluated using a nested polymerase chain reaction (PCR) and discriminating primers based on 25S rDNA polymorphisms to detect different fungal species within root systems. Medicago truncatula was grown in soil of field plots amended or not with a composted sewage sludge, spik ed or not with organic or metallic micropollutants. Overall AM development in roots decreased with sewage sludge application, and the relative abundan ce of five AM fungal morphotypes in root fragments was modified by the inpu t of composted sludges. Sewage sludge spiked or not with organic pollutants had a generally positive effect on the relative diversity of AM fungal pop ulations in planta, whereas after spreading of the sludge spiked with metal lic pollutants, no variation was observed in the abundance of different spe cies.