Abstract
In urban ecosystems – such as parks, trees alignments or industrial wastelands – the composition of ectomycorrhizal communities and its capacity to establish interactions with plants remains poorly documented. However, in the Mediterranean biome, the vast majority of trees and shrubs of urban ecosystems are ectomycorrhizal host plants. Ectomycorrhizal fungi highly contribute to plant establishment, growth and survival through promoting nutrient and water assimilation of nutrients and water by plants. Consequently, ectomycorrhizal fungi are ideal candidates for the development of innovative methods for designing “living soils” at the base of longer-lived plant communities.This PhD project emerges from a societal request and is conducted in close cooperation between fundamental research in community ecology, landscape architecture and public planning engineering. It is based on a molecular analysis of fungal reservoirs in urban soils to develop restoration methods of degraded urban soils and build resilient green spaces. During this work, we first analyzed the scientific corpus available on ectomycorrhizal interaction networks, and more particularly analyzed the state of the art of interactions described in urban soils. We questioned the current limits of metabarcoding methods for the analysis of ectomycorrhizal communities. In a third part, we analyzed the composition of the ectomycorrhizal fungal inoculum present in urban soils excavated after 70 years of sealing. Under the perspective of ecological restoration of such soils, we developed a fungal community inoculation technique based on the addition of a fraction of soil from adjacent natural ecosystems. Three major results emerge from this work:1) In natural ecosystems, the academic corpus on common mycorrhizal networks mainly comes from forest ecosystems. The successional stage of shrubland and anthropized ecosystems having been little regarded.2) Optimal use of metabarcoding to describe the composition of ectomycorrhizal fungal communities could rely on a compromise combining 1) a high number of environmental samples (soils, roots) in order to integrate the patchiness of the communities and 2) a depth modest sequencing, in order to optimize the tool's ability to characterize communities on a reduced number of reads.3) The residual ectomycorrhizal spore bank in sealed soils host degraded ectomycorrhizal communities that are still capable to establish mutualistic interactions with plants after 70 years of isolation in sealed soils. The efficiency of fungal inoculation through the transfer of a fraction of soil from adjacent natural environments was assessed by the effective mobilization of shrublands ectomycorrhizal propagules by seedlings.From an operational perspective, this work highlights the importance of the belowground biotic component of urban ecosystems –and the plant-fungus interactions established in the soil. The restoration of urban soils through the re-inoculation of ectomycorrhizal propagules in the substrate can support the development of long-lived plant communities in vegetated urban areas. This thesis proposes fundamental and applied research avenues to improve our knowledge of the ecology of ectomycorrhizal fungi based on in situ experimentation in cities. It demonstrates the need for reflection on several scales of the landscape, involving the diversity of actors involved in the urban environment.