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Mobilization of organic nitrogen by ectomycorrhizal fungi

Many trees form ectomycorrhizal symbiosis with fungi. During symbiosis, the tree roots supply sugar to the fungi in exchange for nitrogen, and this process is critical for the nitrogen and carbon cycles in forest ecosystems. However, the extents to which ectomycorrhizal fungi can liberate nitrogen and modify the soil organic matter and the mechanisms by which they do so remain unclear since they have lost many enzymes for litter decomposition that were present in their free-living, saprotrophic ancestors.

We have shown that a number of ectomycorrhizal fungi of different evolutionary origin can partly decompose soil organic matter by means of oxidative mechanisms. The oxidation links to a hydrolytic system that participate in the liberation and assimilation of organic nitrogen. We have proposed that the ancestral decay mechanism used primarily to obtain carbon have been adapted in symbiosis to scavenge nutrients instead. In this project, we will in more detail examine how the oxidative and hydrolytic systems are functionally connected and how they are regulated at the level of individual hyphal tips.

A microscope photo with arrows pointing out the interesting structures.
Visualization of an extracellular polymer layer (EPS) surrounding a hyphal tip of the ectomycorrhizal fungus Paxillus involutus. This layer constitutes the contact zone between the hypha and the surrounding environment.

The above photo is recorded by Scanning Transmission X-ray Microscopy (STXM) in collaboration with Martin Obst, University of Beyrueth.

Recent publications

All project publications at the Lund University Publications database

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Funding

Swedish Research Council (VR)