MYCORRHIZAL MEDIATION OF SOIL: FERTILITY, STRUCTURE, AND CARBON STORAGE Johnson, Gehring, Jansa (eds.) Section IV: Mycorrhizal mediation of ecosystem carbon fluxes and soil carbon storage Chapter 19: Introduction: Mycorrhizas and the carbon cycle

Mycorrhizal fungi channel significant amounts of recently fixed plant carbon (C) through the soil, affecting a number of soil processes including the composition and activity of microbial communities and soil organic matter (SOM) mineralization. Some of the mycorrhizal fungi (particularly those establishing ecto-, ericoid and orchid mycorrhizas) can directly mineralize SOM, although often they do not utilize its C, but only the mineral nutrients such as nitrogen and/or phosphorus locked up in it. Arbuscular mycorrhizal fungi lack efficient exoenzymes to mineralize SOM on their own and thus possibly rely on associated microorganisms to do that job. Often, the mycorrhizal fungi effectively deplete their hyphospheres of mineral nutrients such as nitrogen and phosphorus, inducing localized nutrient deficiency of soil microbial communities and resulting in stabilization of soil organic C on a long run. Involvement of mycorrhizal symbiosis in soil C cycling is briefly outlined in this chapter, introducing following chapters that elaborate on this subject from different perspectives.