Back to the roots: Uncovering ectomycorrhizal communities across three major African vegetation types

Ectomycorrhizal fungi (EcM) are critical to the health and sustainability of many African ecosystems that include EcM-associated tree species. In Sub-Saharan Africa, three major EcM-dominated vegetation types can be distinguished: the Central African Guineo-Congolian rainforests, the West African Sudanian woodlands and the East African Zambezian Miombo woodlands. While the rainforests feature humid conditions with isolated patches of EcM trees amongst predominantly arbuscular mycorrhizal (AM) communities, the woodlands are characterised by drier soils and more vast continuous areas of EcM trees. We hypothesise that the isolation of EcM tree patches within the rainforest promotes a unique and potentially endemic EcM fungal community, while riparian forests found along rivers in woodland areas may serve as corridors, facilitating the spread of such rare taxa into woodland regions. In this study, we employ root tip metabarcoding combined with Species Hypothesis (SH) matching to characterise the EcM communities across these three vegetation types. Consistent with previous findings from fruit-body surveys and eDNA studies, our results show that Russulaceae is the most abundant EcM clade across all three regions. Other clades reveal greater discrepancy compared to their above-ground abundances, with notably high abundances of Inocybaceae, Thelephoraceae and Sebacinaceae, especially in woodlands. Conversely, Amanitaceae and Boletaceae appear under-represented. Both Boletaceae and Elaphomycetaceae are found to be more prevalent in rainforest and riparian zones, illustrating the unique EcM community of the Guineo-Congolian rainforest. Our findings highlight the corridor potential of riparian areas in facilitating the spread of these rainforest endemics. This suggests that local edaphic and climatic conditions can override broad spatial patterns, such as distance decay, in community structure of African EcM. Moreover, we suggest a stronger effect of EcM host specificity than previously suggested for African fungal communities. Lastly, we assess the level of species-level representation and accuracy of taxonomic annotation of SHs within African Lactifluus. We confirm it to be one of the most thoroughly described and collected fungal genera on the continent, with over 80% of identified SHs represented in our herbarium collections.