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Revisiting the hypothesis that fungal-to-bacterial dominance characterizes turnover of soil organic matter and nutrients

  • Johannes Rousk
  • Serita D. Frey
Publishing year: 2015
Language: English
Pages: 457-472
Publication/Series: Ecological Monographs
Volume: 85
Issue: 3
Document type: Journal article
Publisher: Ecological Society of America

Abstract english

Resolving fungal and bacterial groups within the microbial decomposer community is thought to capture disparate life strategies for soil microbial decomposers, associating bacteria with an r-selected strategy for carbon (C) and nutrient use, and fungi with a K-selected strategy. Additionally, food-web model-based work has established a widely held belief that the bacterial decomposer pathway in soil supports high turnover rates of easily available substrates, while the slower fungal-dominated decomposition pathway supports the decomposition of more complex organic material, thus characterizing the biogeochemistry of the ecosystem. We used a field experiment, the Detritus Input and Removal Treatments, or DIRT, experiment (Harvard Forest Long-Term Ecological Research Site, USA) where litter and root inputs (control, no litter, double litter, or no tree roots) have been experimentally manipulated during 23 years, generating differences in soil C quality. We hypothesized (1) that delta C-13 enrichment would decrease with higher soil C quality and that a higher C quality would favor bacterial decomposers, (2) that the C mineralized in fungal-dominated treatments would be of lower quality and also depleted in delta C-13 relative to bacterial-dominated high-quality soil C treatments, and (3) that higher C mineralization along with higher gross N mineralization rates would occur in bacterial-dominated treatments compared with more fungal-dominated treatments. The DIRT treatments resulted in a gradient of soil C quality, as shown by up to 4.5-fold differences between the respiration per soil C between treatments. High-quality C benefited fungal dominance, in direct contrast with our hypothesis. Further, there was no difference between the delta(CO2)-C-13 produced by a fungal compared with a bacterial-dominated decomposer community. There were differences in C and N mineralization between DIRT treatments, but these were not related to the relative dominance of fungal and bacterial decomposers. Thus we find no support for the hypothesized differences between detrital food webs dominated by bacteria compared to those dominated by fungi. Rather, an association between high-quality soil C and fungi emerges from our results. Consequently there is a need to revise our basic understanding for microbial communities and the processes they regulate in soil.


  • Environmental Sciences related to Agriculture and Land-use
  • aboveground/belowground
  • biogeochemistry
  • carbon sequestration
  • decomposer ecology
  • food web
  • forest ecology
  • fungal and bacterial
  • dominance
  • Harvard Forest Long-Term Ecological Research (LTER)
  • soil C
  • cycle


  • Interaction between fungi and bacteria in soil
  • Effect of environmental factors on fungal and bacterial growth in soil
  • Microbial carbon-use efficiency
  • MICCS - Molecular Interactions Controlling soil Carbon Sequestration
  • Microbial Ecology
  • ISSN: 0012-9615
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E-mail: johannes [dot] rousk [at] biol [dot] lu [dot] se

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