Impacts of clear-cutting on soil fungal communities and their activities in boreal forests - A metatranscriptomic approach

Abstract: Large-scale forestry has reduced and fragmented the area of primary forest and greatly impacted communities of organisms, above and below ground. Fungal com-munities, which are pivotal in boreal forest soil functions, are vulnerable to tree har-vesting. Changes in their community composition may be followed by loss of key functions and ultimately affect carbon and nutrient cycling. By using various molec-ular approaches, such as metabarcoding, transcriptomics and metatranscriptomics, this thesis aims to investigate how clear-cut forestry affects the composition and traits of soil fungal communities.In a shorter time perspective, clear-cutting eliminate ectomycorrhizal fungi but stimulates growth of saprotrophic fungi. Clear-cutting also enhanced cellulose and lignin decomposition, which may reduce soil carbon stocks in the short-term and potentially cause eutrophication in the mid-term. After 35 years, the ectomycorrhizal fungal community composition in re-established secondary forest was still not re-stored to the same composition as in forest with longer continuity, although its bio-mass had recovered. Particularly Cortinarius, a genus with a key functional role in lignin decomposition, was largely missing in secondary forest. Ectomycorrhizal Cortinarius species accounted for a large fraction of gene transcription of ligninolytic peroxidases in forests with long continuity, and loss of this function could impair long-term nitrogen cycling and soil fertility.Overall, this thesis presents evidence that clear-cutting forestry has extensive ef-fects on fungal biodiversity, with major short-term consequences for soil fungi and their facilitation of decomposition and nutrient cycling, but also long-term effects on ectomycorrhizal communities that should be considered in further evaluation of management practices.

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