Worldwide diversity and ecology of mangrove fungi: a systematic review of ITS metabarcoding studies and a quantitative, integrative analysis of raw sequence data

Fungi are integral components of the mangrove microbiome, playing critical roles in decomposition, nutrient cycling, and symbiosis. Our study synthesizes the findings from a global systematic review of fungal ITS metabarcoding studies conducted in mangrove ecosystems. This review consolidates data from 23 original research articles (1,154 samples) and provides a comprehensive overview of the diversity, community structure, and ecological functions of fungi in these critical coastal habitats. The analyses revealed a consistent core fungal mycobiome in mangroves worldwide. This community is dominated by Ascomycota, with Basidiomycota as the second most abundant phylum. A consistent set of ten highly abundant genera underpins this core community, and fungal diversity and composition are strongly influenced by the specific substrate. Non-rhizospheric sediment harbors the highest diversity, while live plant organs host a more specialized and less diverse community, slightly dominated by potential plant pathogens. Rhizospheric sediment supports a unique assemblage rich in wood-decomposing fungi. The primary ecological role of fungi in mangroves is decomposition, which is essential for breaking down lignocellulosic litter, cycling nutrients, and storing carbon in sediments. A surprisingly high relative abundance of fungi classified as plant pathogens was identified on mangrove plant tissues, suggesting an underappreciated role of fungal diseases in these ecosystems. Metabarcoding provides a far broader view of fungal diversity than traditional collection and culturing methods. It has uncovered a vast number of uncultured taxa and has been particularly effective in revealing the significant, and likely underestimated, presence of macrofungi in mangrove soils. Our study also highlights that current short-read metabarcoding can severely underestimate certain fungal groups, particularly the endomycorrhizal Glomeromycota, due to technical limitations. Altogether, our synthesis provides a global baseline against which future mangrove mycobiome studies can be benchmarked.