16S and ITS communities in bioretention mesocosms in Montreal, Canada

Bioretention systems are green infrastructures increasingly used to manage urban stormwater runoff. Bacteria and fungi appear to play a major role in the bioretentions performance by improving water quality and supporting plant efficiency. However, to date, little is known about these communities and how design choices of BR system influence them. The aim of our mesocosm study was to investigate the influence of different plant species (BioSamples B_), and de-icing salt (BioSamples C_) in stormwater runoff, on the diversity, the composition and the abundance of bacteria and fungi within bioretention. The plant species selected (Cornus sericea, Juncus effusus, Iris versicolor, Sesleria autumnalis) are commonly used in bioretention and differ in terms of biological forms and functional traits. The semi-synthetic stormwater used for watering was supplemented in spring with four NaCl concentrations (0, 250, 1000 or 4000 mg Cl/L) to simulate different degree of de-icing salt runoff. The bacterial and fungal communities were characterized by sequencing respectively the 16S and ITS region. All bioretention mesocosms were naturally colonized by bacteria and fungi adapted to a humid and contaminated environment. Among the taxa abundantly present, several assumed functions that would be useful in improving bioretention performance, such as involvement in the nitrogen cycle, the degradation of hydrocarbons, the tolerance and remediation of metals, or plant symbionts. Others, such as nitrogen-fixing bacteria recruited by Irises could, if active, reduce the nitrogen removal efficiency of BR. Our results suggest the maintenance or restoration of communities and their associated functions, within 5 months after the passage of salt runoff. Our study confirms the importance of the plant species choice on the diversity, composition and relative abundance of bacterial and fungal communities, and its possible consequences on the performance of bioretentions.