Exploring the Interplay between Flavonoid Content and Root Fungal Symbionts in Invasive and Non-invasive Woody Plants.

Biotic interactions with soil microorganisms appear to play a role in plant invasion process, particularly by establishing stronger mutualisms and avoiding antagonistic interactions, although the evidence remains limited. Even less is known about the mechanisms through which invasive plants enhance mutualisms and deter antagonisms. Most of the evidence is restricted to studies on the flavonoid quercetin in roots of seedlings from a limited number of plant species under greenhouse conditions. Using a phylogenetically balanced design, we studied colonization by AMF (mutualists) and dark septate endophytic fungi (DSE) (presumed mutualists), as well as by Olpidiaster sp. (antagonist) in nine pairs of woody plant species under field conditions -invasive alien and non-invasive native-. We also analyzed flavonoid content, the presence of four flavonols, and examined their relationships with fungal colonization. Invasive alien species exhibited higher levels of arbuscule colonization by AMF, although no such pattern was observed for DSE colonization. While the antagonist Olpidiaster sp. showed lower colonization in invasive species, the differences were not significant. Flavonoid content and flavonol richness did not differ between invasive and non-invasive native species. However, we observed a negative correlation between root flavonol richness and AMF colonization, strikingly in invasive woody species but not in non-invasive natives. These novel findings highlight the dynamic nature of flavonoid production in the roots of invasive plants and its interactions with novel soil AMF in foreign ecosystems, shedding light on the potential role of chemical traits in shaping invasive plant biotic interactions.