Project R-3182

Exploring the mechanisms of organic matter degradation by ectomycorrhizal fungi: how much do they contribute to organic C and N mobilization? (Research)

In temperate forests, accessibility of nitrogen is the most important determinant of tree productivity. Symbiotic ectomycorrhizal fungi (ECMs) allow trees to access nitrogen sources that are otherwise unavailable to trees, through the secretion of enzymes, which degrade organic matter. However, in forest soils, ectomycorrhizae are in competition with other fungi living on dead plant material for retrieving nitrogen. Indeed, the relative contribution of ectomycorrhizal fungi in the organic matter degradation is hard to estimate. This degrading ability is commonly measured with enzymatic assays that are poorly representative for field conditions. To fully understand the degradation pathways, it is necessary to investigate a vast array of enzymes because of the chemical complexity of organic matter. Eventually, some non-enzymatic mechanisms can also be involved in organic matter degradation. The aim of this project is to assess in detail the degradation of organic matter and the acquisition of organic nitrogen by ectomycorrhizae, using new exhaustive and field-based approaches. We hypothesize that the organic matter degradation by ECMs has been underestimated and that these fungi are able to deeply modify and transform complex organic matrices, through the secretion of enzymes poorly detected by conventional assays and (or) by using non-enzymatic mechanisms.

01 October 2011 - 30 September 2014