Dual mycorrhizal associations in tea tree (Melaleuca alternifolia) differ between Australian temperate shrublands and subtropical forests

Abstract

Background & aims: Tea tree (Melaleuca alternifolia) is an economically important crop with a narrow natural distribution in eastern Australia. Coastal and upland tea tree ecotypes have been identified based on unique shoot and root traits, but their mycorrhizal associations remain unknown. Dual mycorrhization—the ability of plants to associate with both arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) fungi—is particularly common among Australian Myrtaceae, including Melaleuca species, but has not yet been investigated in tea tree. Methods: We investigated the mycorrhizal associations of tea tree in three coastal and two upland populations using ITS2 metabarcoding and root anatomical observations. Results: Our results revealed that tea tree is a dual mycorrhizal plant, showing variability in root symbioses among ecotypes. ECM percentage root colonisation was significantly lower in the coastal tea tree ecotype compared to the upland ecotype, despite the coastal ecotype exhibiting significantly higher levels of ECM fungal richness. In contrast, the richness of the AM order Glomerales was significantly higher in the coastal tea tree ecotype than in the upland ecotype, yet comparable levels of AM root colonisation were observed between these two ecotypes. Mycorrhizal fungal community composition also differed significantly between coastal and upland ecotypes. Conclusions: Our study provides evidence that tea tree is a dual mycorrhizal species that can host AM and ECM fungi simultaneously within individual plants. Our findings suggest that coastal and upland tea tree ecotypes vary in their associations with mycorrhizal fungi across native habitats, which differ in climate, soil characteristics, and vegetation structure.