C:N Interactions and the Cost:Benefit Balance in Ectomycorrhizae

Abstract

The exchange of nutrients for carbon (C) is the very core of mycorrhizal (M) associations, and unraveling the C and nutrient fluxes between symbionts is at the core of its understanding. The role of ectomycorrhizae (ECM) in the plants nitrogen (N) nutrition is particularly important. In this chapter, the interactive role of N and C in the physiology of ECM is analyzed. Current knowledge on C and N fluxes between symbionts is reviewed. The balance between C cost and nutrient gain is traditionally considered to determine if the plant benefits or not from mycorrhization. Mycorrhizae are traditionally accepted as being mutualisms, and therefore beneficial for both plant and fungal partners. This concept has been recently challenged and replaced by the growing belief that they can vary from mutualistic through to parasitic in a continuum of responses. This is analyzed and discussed in the light of recent findings and with a focus on C:N balances and fluxes between symbionts.