Humans are notorious for disturbing terrestrial ecosystems worldwide, especially those that are in close proximity to urban areas. This disturbance has involved the accumulation of various types of chemical pollutants, of either agricultural or industrial origins, in both soil and water ecosystems. Pollutants have sometimes included essential plant nutrients, such as phosphate and nitrate, which have piled up throughout the years in many ecosystems as a consequence of aggressive agricultural practices, and a number of toxic or trace metals, e.g. iron, nickel or zinc that are important at low levels for the fitness of living organisms, but otherwise toxic at high concentrations (Ker & Charest 2010; Audet & Charest 2008). In order to reduce the load of toxic elements, scientists have used the natural capacity of several plant species to sequestrate them from the soil and, ultimately, render them harmless. This process, called phytoremediation, is rather slow, as most plants take years to build up their biomass but has been shown to be ‘boostable’ under experimental conditions in the presence of a particular group of plant symbionts in the soil – the arbuscular mycorrhizal fungi (AMF) (Gohre & Paszkowski 2006). These latter organisms are now widely recognized as being very beneficial for purposes of phytoremediation, but their biodiversity in the most disturbed ecosystems is still virtually unknown. Are these fungi really abundant in heavily polluted soils, or are their communities shrunken down like those of other microorganisms in the presence of heavy pollution? In this issue of Molecular Ecology, the study by Hassan et al. (2011) provides answers to these specific questions by determining the extent of AMF biodiversity across several urbanized areas in the City of Montréal.