Links between boreal forest management, soil fungal communities and belowground carbon sequestration

Forest management has a potential to alter belowground carbon storage.
However, the underlying mechanisms, and the relative importance of carbon
input and decomposition in regulation of soil carbon dynamics are poorly
understood. We examined whether interactive effects of forest
fertilization and thinning on carbon stocks in the topsoil of boreal
forests were linked to changes in fungal community composition, biomass,
and enzyme activities, in a long-term fertilization and thinning
experiment distributed across 29 Pinus sylvestris forests along a 1300 km
latitudinal transect in Sweden. Nitrogen fertilization increased fungal
biomass, particularly towards the north and mainly by promoting root
associated Ascomycetes, but the response was moderated by thinning. Fungal
biomass correlated positively with carbon stocks in the organic topsoil.
However, ectomycorrhizal Cortinarius species were reduced in abundance by
fertilization and correlated negatively with carbon stocks. Plausibly,
increased soil carbon stocks after fertilization are linked to increased
input of carbon in the form of root-associated mycelium combined with loss
of ectomycorrhizal decomposers within the genus Cortinarius. These fungal
responses to fertilization may mediate a natural climate solution by
promoting carbon sequestration in the organic topsoil, but the effect of
fertilization may also be undesired from a biodiversity perspective.