Mutualistic mycorrhiza in orchids: Evidence from plant-fungus carbon and nitrogen transfers in the green-leaved terrestrial orchid Goodyera repens

Abstract

• The roles of mycorrhiza in facilitating the acquisition and transfer of carbon (C) and nitrogen (N) to adult orchids are poorly understood. Here, we employed isotopically labelled sources of C and N to investigate these processes in the green forest orchid, Goodyera repens. • Fungus-to-orchid transfers of C and N were measured using mass spectrometry after supplying extraradical mycelial systems with double-labelled [13C- 15N]glycine. Orchid-to-fungus C transfer was revealed and quantified by radioisotope imaging and liquid scintillation counting of extraradical mycelium following 14CO2 fixation by shoots. • Both 13C and 15N were assimilated by the fungus and transferred to the roots and shoots of the orchid. Contrary to previous reports, considerable quantities (2.6%over 72 h) of fixed C were shown to be allocated to the extraradical mycelium of the fungus. • This study demonstrates, for the first time, mutualism in orchid mycorrhiza, bidirectional transfer of C between a green orchid and its fungal symbiont, and a fungus-dependent pathway for organic N acquisition by an orchid. © New Phytologist (2006).