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Fungal guild interactions slow decomposition of boreal forest pine litter and humus

Summary

In boreal forests, different types of fungi compete with each other to break down dead plant material. This study found that the fungi living in partnership with tree roots actually slow down the decomposition of fresh pine needles, especially after droughts. However, in older, partially decomposed soil material, the fungi associated with tree roots actually speed up decomposition, while fungi associated with shrubs slow it down. These findings suggest that how quickly different types of fungi decompose forest material depends on what type of dead material they are breaking down.

Background

Ericaceous understory shrubs and their associated mycorrhizal fungal communities are ubiquitous in boreal forests. Ectomycorrhizal fungi are thought to suppress saprotrophic decomposition through competition for nitrogen, potentially explaining why ectomycorrhizal-dominated forests accumulate more soil organic matter. The relative importance of interactions between ectomycorrhizal, ericoid mycorrhizal, and saprotrophic fungi in controlling organic matter dynamics remains unclear.

Objective

To evaluate the effects of fungal guilds on decomposition of pine needle litter and humus in boreal forest. The study tested the Gadgil effect and mycorrhizal guild hypothesis using a factorial field experiment with shrub removal and pine root exclusion treatments.

Results

Pine needle litter decomposition was 23% greater when ectomycorrhizal fungi were excluded, demonstrating a Gadgil effect that emerged after 17 months following summer drought. Humus decomposition was stimulated by ectomycorrhizal fungi but counteracted by ericoid mycorrhizal shrubs. White rot saprotrophs were positively associated with litter decomposition while nonwhite rot saprotrophs were negatively associated.

Conclusion

Competitive saprotrophic-ectomycorrhizal fungal interactions may slow early-stage litter decomposition, though this effect was small and inconsistent. Interactions between ecto- and ericoid mycorrhizal guild members appear to determine late-stage organic matter balance in boreal forest humus, suggesting the Gadgil hypothesis cannot be simply extrapolated from litter to humus decomposition.
  • Published in:New Phytologist,
  • Study Type:Field Experiment,
  • Source: PMID: 40552521, DOI: 10.1111/nph.70316
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