Stronger legacy-effects of forest fertilization on soil saprotrophic fungi than on ectomycorrhizal fungi in the first decade after clearcutting

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Intensive forest management practices, such as fertilization and clearcut harvesting, are known to severely disturb biodiversity in boreal forests, but to what extent fertilization effects are still detectable after clearcutting is currently not well understood. Here we used a space-for-time approach in clearcuts of fertilized and unfertilized forests to study the dynamics of soil fungal communities after clearcutting. We re-analysed data on fungal communities in the soil organic layer of 48 clearcuts in Sweden, spanning 1-13 years post-harvest. Clearcuts of previously fertilized forests were paired with clearcuts of unfertilized forests with similar characteristics. Ectomycorrhizal fungi disappeared after clearcutting, while saprotrophic fungi initially increased in abundance and subsequently decreased as ectomycorrhizal fungi reappeared. This effect was especially pronounced for saprotrophic agaricomycetes (Mycena, Luellia, and Trechispora) and in clearcuts of fertilized forests. We conclude that certain saprotrophic agaricomycetes respond to a transient release from Gadgil suppression by ectomycorrhizal fungi and/or an increase in substrate availability after clearcutting. Saprotrophs were particularly prolific in previously fertilized stands, in line with rapid disappearance of additionally accumulated belowground organic matter, whereas ectomycorrhizal fungal communities were little impacted by previous fertilization during the first decade after clearcutting.

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