Fungal molecular ecology in boreal forests and challenges associated with unidentified environmental DNA sequences

Sammanfattning: Many fungi are characteristically difficult to observe and collect, making the process of documenting the world’s fungal diversity challenging. The vast majority of fungal species are undescribed. The use of DNA sequencing technologies has revolutionized the study of fungal diversity by facilitating the detection of new species, the investigation of community  structure and dynamics, and the elucidation of evolutionary relationships. In this dissertation, I focus on filling in some of the many gaps in our understanding of fungal diversity and community ecology in boreal pine forests through the use of DNA sequence data. In the first half of this thesis, a metabarcoding approach is used to study the composition of fungal communities found in the soil of a Lithuanian coastal pine forest and in association with the bark beetle Tomicus piniperda in Swedish pine forests. In the second half, two different approaches are taken to describe taxa detected in environmental DNA. In paper I, I demonstrate how soil microhabitats, defined based on mineral vs organic soil type and root presence or absence, vary with respect to a suite of abiotic factors and shape fungal community composition belowground. These microhabitats support functionally and taxonomically distinct fungal communities and support the overall fungal diversity of the site through niche variation. In paper II, the relationships between a) the fungal communities found on and in bark beetles from forests that have been affected by forest fire and forests that have not, b) pine phloem that has been colonized by bark beetles and phloem that has not at two different post-colonization time points, and c) phloem chemical nutrients are described. In paper III, the diversity of species within the fungal class Archaeorhizomycetes in the soil of a Swedish pine forest was studied, and two new species are described using an integrative taxonomic approach that relies on environmental DNA sequence data as taxonomical evidence. Finally, in paper IV, a new class is described to accommodate a lineage previously detected in environmental DNA, and its first known species is described based on isolates collected during the study of paper III, one of which serves as the type specimen.