Do mycorrhizal fungi create below-ground links between native plants and Acacia longifolia? A case study in a coastal maritime pine forest in Portugal

Abstract. Maritime pine forests are a major ecosystem throughout the Portuguese coast and are severely affected by the invasion of Acacia longifolia. The presented study investigated the diversity of ectomycorrhizal fungi (ECM) of major plant species in these ecosystems to find possible links between Pinus pinaster, three native Cistaceae shrubs and the Acacia invasive species. We successfully identified 13 ECM fungal taxa. Within those, two species from the order Helotiales were found in all plant species, and over half of the fungal ECM species found in Pinus pinaster were also common to the Cistaceae shrubs. Network analysis points to the Cistaceae shrubs having a central role in these below-ground communities, therefore enforcing the idea that they are key to these communities and should not be underestimated. Our results also point to the evolving role of invasive plant species in the ecosystem dynamics in the rhizosphere, which host fungal species that are common to native plants, although it is not yet clear whether these fungal taxa are native or a consequence of the presence of Acacia longifolia.