10 Mycorrhizal Fungi and the Soil Carbon and Nutrient Cycling

Abstract

``Mycorrhiza'' is a generic word used to designate usually beneficial, mutualistic associations between plant roots and fungi. All mycorrhizae share the presence of fungal hyphae forming characteristic symbiotic structures within plant roots, which are connected to external hyphae that grow outwards, exploring the surrounding soil matrix (Smith and Read 2008). Besides these shared characteristics, it has long been recognized that mycorrhizae encompass plant-fungal associations of distinct evolutionary origins (Smith and Read 2008; van der Heijden et al. 2015). However, despite these distinct origins, a classical and unified vision of mycorrhiza describes this association as a ``balanced'' plant-fungus partnership where each of the two associates provides essential nutrients to the other one at the plant-fungal interface (either a Hartig net, arbuscules, or pelotons) (Brundrett 2004). In such a classical model, plants allocate to their fungal partners photosynthesis-derived simple sugars (mono- and/or disaccharides) in exchange for soil-derived macronutrients (e.g., nitrogen, phosphorus, potassium) provided by the fungi.