Uncovering the decomposer capacity of ectomycorrhizal fungi

Ectomycorrhizal fungi form a symbiotic exchange with trees, by providing the trees with otherwise unavailable nutrients in return for photosynthetic sugars. Nitrogen is often bound to organic matter that is difficult to degrade, but some ectomycorrhizal fungi have the capacity to produce enzymes which can release the nitrogen. In her thesis, Erica Packard at the Department of Soil and Environment has investigated these specialised fungi, here called ectomycorrhizal decomposers. Together the studies in her thesis suggest that ectomycorrhizal decomposers are important in nutrient cycling and organic matter decomposition.

Not all species sensitive to forestry

She found that not all fungi species within a genus have the same potential as decomposers, which means we need a better understanding on species level to be able to protect the species important for the soil ecosystem. 

Using data from the Swedish Forest Soil Inventory at SLU, Erica Packard also found that the specialised fungi species thrive in a variety of forests, not only in older forests with low forestry impact. 

− It was expected that these fungi would be more sensitive to disturbances in comparison to other ectomycorrhizal fungi, but this was not the case for all species. However, we only assessed the niche of a small group of relatively common fungi, and many other species are negatively impacted by intense forest management, says Erica Packard.

Specialised enzyme activity

Erica Packard investigated the enzyme activity of an ectomycorrhizal fungus by inserting a gene from this fungus into an easy-to-grow yeast. From this she could see that the ectomycorrhizal enzymes had activities, but that they were different than enzymes produced by other decomposer fungi. 

− This indicates that these specialised ectomycorrhizal fungi may indeed have a similar capacity to other decomposer fungi. But more research is needed to understand the mechanisms of the enzymes they produce, says Erica Packard.

Nitrogen unbound

To see whether the fungi used these enzymes for releasing nitrogen Erica Packard used RNA-sequencing. She found a clear positive relationship between the use of genes for this enzyme and genes for enzymes that break down organic sources of nitrogen.

− This supports that ectomycorrhizal decomposers use these enzymes to increase access to nitrogen bound in organic matter. Thereby, they may be able to maintain nutrient cycling and tree productivity in nitrogen-limited soils. However, this mining for nutrients may also increase the release of carbon from the soil and therefore restrict the potential for soil carbon storage, says Erica Packard. 

Dissertation

Link to the dissertation: Ectomycorrhizal decomposers – enzymes, ecology, and evolution

Erica Packard defends her dissertation on the 29th of May 2026 at 13.00 in Hall L in the Educational Buildning, Campus Ultuna, Uppsala. Registration to: Johan.Stendahl@slu.se