Variability in the dual mycorrhizal associations of tea tree, Melaleuca alternifolia

Abstract Background & aims. Tea tree (Melaleuca alternifolia) is an economically important crop plant with a limited natural distribution in eastern Australia. Coastal and upland tea tree ecotypes have been identified based on unique shoot and root traits. Dual mycorrhization, the ability of plants to associate with both arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) fungi, is particularly frequent among the Australian Myrtaceae, including Melaleuca species. However, the mycorrhizal type of tea tree is currently unknown. Methods. We investigated tea tree mycorrhizal associations 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 populations. We found that ECM percentage root colonisation was significantly lower in coastal tea tree populations compared to upland populations, despite coastal tea tree populations exhibiting significantly higher levels ECM fungal richness. In contrast, we showed moderate evidence that AM richness was higher in coastal tea tree ecotypes than in upland ecotypes, yet comparable levels of AM root colonisation were observed between ecotypes. Mycorrhizal fungal community composition also differed significantly between coastal and upland plants. 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 environmental factors among coastal and upland sites, particularly soil drainage and nitrogen availability, can affect mycorrhizal traits in native tea tree populations.