Respiratory Costs of Mycorrhizal Associations

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Mycorrhizal fungi form symbiotic and often mutually beneficial relationships with the roots of most terrestrial plants. In this chapter we review current literature concerned with plant respiratory requirements for supporting this important plant-fungal association, and its effect on the overall plant carbon economy. Controlled studies indicate that mycorrhizal respiratory costs are considerable, consuming between 2 to 17% of the photosynthate fixed daily, varying depending on the host and fungal species involved, the stage of colonization, and the environmental conditions. Respiratory energy is required by the mycobiont for construction of new intraradical and extraradical fungal tissue (including reproductive structures), for maintenance and repair of existing fungal tissue, and for cellular processes in the fungal tissue associated with the absorption, translocation and transfer of nutrients from the soil to the host. Additional respiration is also required by the host plant for stimulated root cellular processes, and potentially for increased production of root biomass. Field studies of these important processes will eventually lead us to better understand how significant mycorrhizal fungi are to the total carbon budgets of natural and managed plant communities.