Nitrogen (N) is the main limiting factor for tree growth in forest soils, and is present there mostly in an organic form, either sequestered within dead plant cells or complexed with cell wall components such as lignins and their phenolic derivatives. Ectomycorrhizal fungi are able to retrieve significant amounts of N from organic pools in forest soils, however most of the literature on the subject report that they have low ability to secrete significant amounts of enzymes that can degrade organic matter.
We investigate how a model extomycorrhizal fungus, Paxillus involutus, is able or not to degrade organic matter and retrieve N from complex organic material. For this purpose, we are combining measurements of secreted organic matter degradation activities to an analysis of transcript presence and regulation (454 EST sequencing and microarray) and to a wide spectrum of complementary techniques characterizing the chemical modifications occurring in the organic matter substrate. We also measure how these activities are modified by soil bacterial communities and how they are regulated by glucose and inorganic nitrogen.
In parallel, we are also trying to understand how Paxillus involutus is modifying the recalcitrance of organic matter to degradation by other soil microorganisms.
Rineau F., Garbaye J., 2009. Does forest liming impact the enzymatic profiles of ectomycorrhizal communities through specialized fungal symbionts? Mycorrhiza, 19: 493-500.
Rineau F., Garbaye J., 2010. Effects of Liming on potential oxalate secretion and iron chelation of beech ectomycorrhizal root tips. Microbial Ecology, 60: 331-339.
Rineau F., Courty P. E., 2011. Secreted enzymatic activities of ectomycorrhizal fungi as a case study of functional diversity and functional redundancy. Annals of Forest Science, online first.