Year: 2012
Type: dissertation
Abstract: Boreal forest ecosystems constitute a globally important carbon (C) sink, due to \naccumulation of complex organic matter, persistent to decomposition. Nitrogen (N) is \nimmobilized in these complex compounds and, thereby, unavailable to the plant \ncommunity. Fungal peroxidases (ClassII) are oxidative enzymes, predominantly \nstudied in white-rot wood decomposers and known to efficiently mineralize phenolic \ncomplexes, such as lignin, to CO2. Peroxidase activity is also commonly measured in \nforest soil, where typical white-rotters are absent and ectomycorrhizal fungi \npredominate. Peroxidase activity is known to increases under low inorganic N \navailability. The aim of this study was to explore the ectomycorrhizal decomposer \npotential in boreal forest ecosystems. The central hypothesis is that ectomycorrhizal \nfungi produce ClassII peroxidases to mobilize N, bound to phenolic complexes in \nboreal forest litter and humus. \n \nGenes coding for ClassII peroxidases were found to be widely spread among \nectomycorrhizal taxa, particularly within the genus of Cortinarius. Gene transcription \nof peroxidases in forest humus could be linked directly to the species Cortinarius \nsemisanguineus. In a field experiment, colorimetric enzyme assays showed a halving of \nperoxidase activity in short-term response to N-amendment. In non-treated control \nsamples, Cortinarius species and other rhizomorph forming ectomycorrhizal fungi \nwere co-localized with peroxidase activity hotspots. Ectomycorrhizal Cortinarius \nspecies may, thus, be key players in N-acquisition, from organic macromolecules, and \ncentral decomposers of complex organic matter in boreal forest ecosystems. \n \nRoot-associated fungi, including ectomycorrhizal ones, were able to compete with \nfree-living saprotrophs for colonization of litter. However, they were less efficient \ndecomposers than specialized litter saprotrophs. \n \nIt is concluded that some mycorrhizal fungi may release C while foraging for N. \nThey may also indirectly act to preserve soil C by suppressing more efficient \nsaprotrophic decomposers. The findings highlight ectomycorrhizal fungi as central \nregulators of C dynamics in boreal forests. Ectomycorrhizal symbiosis, thus, constitutes \na direct link between above-ground photosynthesis and below-ground decomposition.
Author: Inga T. M. Bödeker
Language: English
Subfield: Plant Science
Domain: Life Sciences
SDG: Life on land
Open Access status: green
OpenAlex ID: W60412247