Phylogenetically distant but cohabiting: Fungal communities of fine roots in Diphasiastrum complanatum,Pinus sylvestris, and Vaccinium myrtillus in a Lithuanian pine forest

Abstract Throughout evolution, distinct plant lineages independently established mutualistic relationships with various fungal taxa. However, the extent to which these relationships are conserved across different plant and fungal lineages remains unclear. In this study, we compared fungal communities associated with the fine roots of three phylogenetically distant yet cohabiting plant species: Diphasiastrum complanatum, a member of lycophytes, the most basal extant vascular plant lineages; Pinus sylvestris, a gymnosperm; and Vaccinium myrtillus, an angiosperm, an evolutionary relatively young lineage. To minimize environmental variability, fine roots of three species were collected from each of 19 five-square-meter plots within a Scots pine forest in Lithuania. Using metabarcoding and microscopic techniques, we observed significant differences in the fungal community composition and diversity among the three plant species. We detected no signs of arbuscular mycorrhiza in any species. Samples of D. complanatum showed significantly higher taxonomical diversity, while P. sylvestris showed lowest diversity, with ectomycorrhizal fungi being most abundant. Samples of V. myrtillus had a prevalence of putative ericoid mycorrhiza taxa, classes Sebacinales and Trechisporales, likely forming hyphal coils detected through microscopy. In contrast, no mycorrhiza was detected in D. complanatum sporophytes. This, along with the presence of well-developed root hairs and similarity to the fungal community inhabiting soil suggests a low dependency on mycorrhizal associations and a more opportunistic fungi-plant relationship. This is the first study of fungi associated with the sporophytes of D. complanatum. Our findings provide valuable insights into the complex interactions between fungi and plants from diverse phylogenetic lineages in natural environments. Competing Interest Statement The authors have declared no competing interest. Abbreviations - RAF - root associated fungi - AM - arbuscular mycorrhiza - OTU - operational taxonomic unit - ECM - ectomycorrhiza - ERM - ericoid mycorrhiza - NTC - non-template control