Carbon Fluxes in Mycorrhizal Plants

Although declared as a research priority more than 40 years ago, the knowledge about the magnitude and mechanisms of carbon (C) fluxes between plants and their mycorrhizal fungal symbionts remains fragmentary. In spite of a number of experiments with isotopically labeled C documented rapid and directed C transfer from the host plant to its mycobionts, the molecular mechanisms and their regulation involved in such a transport remain largely unknown. It seems that in many arbuscular mycorrhizal (AM) symbioses, the C costs remains well below 10% of the C fixed photosynthetically by the host plants. Higher values were detected in the past only under specific situations such as in young plants, under low light intensities, and/or for particular partner combinations, involving very costly (in terms of C demand) and little nutritionally beneficial AM fungi such as Gigaspora sp. Ecological context of the common mycorrhizal networks in terms of redistribution of symbiotic C costs and nutritional benefits on one hand and C movement through soil food webs beyond mycorrhizal hyphae on the other are briefly discussed in this chapter, and further research challenges and open knowledge gaps with respect to C fluxes in mycorrhizal plants are outlined.