Taxonomy, phylogeny, diversity and host preference of leaf litter inhabiting microfungi across six host species in northern Thailand

Leaf litter plays an essential role in the functioning of forest ecosystems. They are a source of organic matter, act as a protective layer in forest soils, and provide a nurturing habitat for micro- and macro-organisms. Through their successional occurrence, litter-inhabiting microfungi play a key role in litter decomposition and nutrient recycling. Despite their importance in terrestrial ecosystems, host tree species and phylogenies’ effect on saprobic fungal dominance and diversity are poorly understood. The present study aims to elucidate saprobic leaf-litter fungal taxonomy, phylogeny and diversity in six phylogenetically related host species in Thailand, using morphological characters and multi locus phylogeny. The host species are Dipterocarpus alatus (DA) (Dipterocarpaceae), Nayariophyton zizyphifolium (NZ) and Microcos paniculata (MP) (Malvaceae), Afzelia xylocarpa (AZ), Dalbergia cana (DC), and Dalbergia cultrata (DCul) (Fabaceae), located in Doi Tung, Chiang Rai Province, Thailand. The selected host species are mostly native to the East Asian region. We hypothesized that tree host phylogeny significantly influences the diversity of fungal communities, and that each community is unique across phylogenetically distantly related hosts. The study revealed one family, two new genera, 15 new species, 13 new host records, and 11 new geographical records with two new combinations of fungi which are treated in detail. Additional taxa identified, mostly to the genus level, were considered for the statistical analysis. In cases where different taxa within the same genus were found but could not be identified to species, they were treated as distinct taxa (e.g., sp. 1 and sp. 2). The statistical analysis was performed to estimate the diversity and relative abundance of each taxon visualized in heatmaps and cluster analysis. The study evidenced multiple levels of diversity and host-preference existing within leaf litter fungi. The reported taxa belonged to the Dothideomycetes and Sordariomycetes, 25 families and 31 genera. Most of the saprobic fungi exhibited host-exclusivity, meaning they were observed and recorded exclusively on specific host species and not on others. This resulted in a lower occurrence and overlap of fungi among the other host species. Therefore, the saprobic fungi indicated specialization on particular hosts, and the term "specialists" referred to the saprobic fungal taxa that are adapted to thrive on specific host species, rather than generalists that can inhabit multiple host species. Host family level harboured a higher number of unique saprobic taxa than host species level, as evidenced by the statistical analysis. Moreover, the saprobic fungal communities were influenced by seasonal effects during the collecting period. A core group of fungi could be identified as “generalists” observed in all the host species. The study highlights the diversity of saprobes dwelling in the leaf litter of forest ecosystems and reveals their high degree of host species-specificity.