After-sealing life in urban soils: Experimental evidence of resilience and efficiency of ectomycorrhizal inoculation

Abstract

The restoration of urban sealed soils is a major stake for urban planners. In particular, characterizing their resilience from a biotic perspective is of primary importance for remobilizing these artificialized substrates in urban green spaces. Using Marseille (France) as a case study, we implemented a metabarcoding next generation sequencing approach to characterize the diversity and the composition of ectomycorrhizal (EM) fungal communities present in soils sealed for 60 years. Based on an inoculation experiment, we tested the ability of the remaining spore bank to establish EM interactions with plants. Altogether, we aimed at assessing the potential of peri-urban natural habitats to provide an efficient soil EM inoculum for the restoration of urban soils. We found that: (i) long-term sealing drastically reduced the diversity of EM fungi in urban soils, (ii) long-leaved spores of hypogeous gastroid fungi were efficient to establish EM symbioses with plants, and (iii) the efficiency of EM fungal inoculation depended on the natural habitat used as an inoculum source. Oak forests provided species-rich but poorly efficient inoculum. Contrastingly, soils collected in disturbed shrublands (garrigues) hosted moderately-rich EM communities containing droughtadapted species with high ability to colonize urban soils. Our findings highlight that peri-urban landscapes are promising candidates to feed local systems of urban soil restoration. In this perspective, poorly-considered habitats such as shrublands can be considered as valuable sources of soil biota to prevent the over-exploitation of agricultural areas.