Factors shaping the similarities and differences between soil mycobiota of Fagus sylvatica and Abies alba in the Easter Carpathians

We explored the mycobiome diversity in the rhizospheres of monumental beech and fir trees in Dentario glandulosae-Fagetum of Bieszczady National Park (eastern Poland) in May and October 2023. The rhizospheres of mature trees can provide a refugium for fungal species not found in younger fragments of an area, thus increasing the potential for resilience to environmental change. We have sequenced soil eDNA isolates from five groups of trees with a dominant species of Common Beech and five of Common Fir, sampling seven trees per site plus sampling between trees. The sites were located close to the lower forest boundary, between 640 and 840 m above sea level, spaced about 1 km apart. Taxonomic analysis and hierarchical clustering showed that fungal species and their abundance varied between beech and fir, more than across spring and autumn at the same site. Categorising species into FungalTraits based trophic guilds revealed a seasonal functional shift: tree-symbiotic fungi were prevalent in spring, while litter decomposers dominated in autumn. This shows that fungal communities in rhizospheres of old trees does not go through species turn-over during yearly cycles, but rather changes in abundance of species performing different trophic roles.