Effect of different composts on the dynamic of soil organic pollutants, microbial network interactions and multifunctionality in an urban garden made from a former brownfield

Brownfield requalification in urban areas can enable their ecological reclamation by improving their ecosystem services. In this perspective, their transformation into urban farms is underexplored due to the potential risks associated with pollutants transfer into vegetables and their low soil functionality. The current study aims to improve soil quality based on the principles of circular economy and to assess the transfer of organic pollutants into vegetables produced in an urban farm built from a former brownfield. For this purpose, locally available composts made from manure, leaves and fragmented rameal wood (FRW) were applied to a plot of a brownfield being converted into an urban garden in Roubaix (France). Thereafter, mixed vegetables (carrot, onion, radish, zucchini, potato, and chard) were cultivated for six months. After harvest, soil microbial communities were studied using metabarcoding of 16S RNA gene and ITS region, along with the dynamic of organic pollutants (petroleum hydrocarbons, dioxins/furans) in the soils and the produced vegetables. Globally, our results showed that the concentrations of these pollutants in vegetables were similar to those of vegetables originating from non-contaminated soils. Compost applications shaped the composition of soil bacterial communities and improved soil total metabolic activity and richness. Furthermore, amendment with manure and FRW composts improved the proportion of positive interactions between fungal and bacterial communities, suggesting more bacteria-fungi facilitation for SOM decomposition and nutrient recycling. Consistently, the calculated ecosystem service metrics and the soil quality index (T_SQI) showed a higher efficiency for FRW compost, demonstrating a relationship between soil microbial network characteristics and functioning.