Soil organic matter decomposition mechanisms in ectomycorrhizal fungi

In boreal forests, ectomycorrhizal (ECM) fungi are found in soil layers containing decomposed litter and humus-rich soil organic matter (SOM). This chapter summarizes the present understanding of the mechanisms for oxidative decomposition of SOM and the hydrolysis and mobilization of organic N and P sources by ECM fungi. It discusses how these processes may influence the formation and stability of SOM, and the interactions with saprotrophic microorganisms in forest ecosystems. The chapter gives a brief introduction to litter decomposition mechanisms in saprotrophic fungi. To investigate experimentally the capacity of ECM fungi to decompose humic-rich SOM and the mechanisms underlying this decomposition, a series of experiments have been conducted using Paxillus involutus as a "model" species. ECM fungi have evolved from diverse nutritional backgrounds, including litter decomposers and WR and BR wood decayers. During these transitions, ECM lineages lost many genes related to saprotrophy. There is evidence that some ECM employ the Fenton reaction during SOM decomposition.