A group of ectomycorrhizal fungi restricts organic matter accumulation in boreal forest

Boreal forest soils are important global carbon sinks, with significant
storage in the organic topsoil. Decomposition of these stocks requires
oxidative enzymes, uniquely produced by fungi. Across Swedish boreal
forests, we found that local carbon storage in the organic topsoil was 33%
lower in the presence of a group of closely related species of
ectomycorrhizal fungi – Cortinarius acutus s.l.. This observation
challenges the prevailing view that ectomycorrhizal fungi generally act to
increase carbon storage in soils but supports the idea that certain
ectomycorrhizal fungi can complement free-living decomposers, maintaining
organic matter turnover, nutrient cycling and tree productivity under
nutrient-poor conditions. The indication that a narrow group of fungi may
exert a major influence on carbon cycling questions the prevailing dogma
of functional redundancy among microbial decomposers. Cortinarius acutus
s.l. responds negatively to stand-replacing disturbance, and associated
population declines are likely to increase soil carbon sequestration while
impeding long-term nutrient cycling.