Earthworms as conveyors of mycorrhizal fungi in soils

Earthworms are emblematic soil organisms, known to be highly beneficial to soil functioning and ecosystem sustainability. In the current context of agroecological transition, they can be inoculated in degraded soil for their beneficial effect on soil structure and plant growth. We here advocate that earthworms can be also used as conveyors of beneficial mycorrhizal fungi in soils, thus enhancing plant nutrition and promoting primary production. Through a review of the literature on earthworms and mycorrhizal fungi, this paper aims at answering the following questions: Do earthworms ingest mycorrhizal fungi? Do they convey mycorrhizal fungi in their digestive tube so they are still active when leaving earthworm intestines? Is there a spatial correlation between earthworm casts and plant roots which could enhance mycorrhizal colonization of the root system? Considering that earthworms may ingest, transport, keep active in their intestine and bring mycorrhizal fungi to the roots, they could be used as conveyors of mycorrhizal fungi in soils. Although depending on the species, their presence was found to improve the colonization of roots by mycorrhizal fungi and to increase significantly the mycorrhization percentage. This perspective paper also underlines precautions that should be taken to make available and relevant this Nature-based soil improvement method.