Mycorrhiza — diversity and impacts

Abstract

Seedlings of Pinus densiflora colonized by an unidentified ectomycorrhizal fungus (T01) were labelled photosynthetically with ¹⁴C. Movement of ¹⁴C-labelled photosynthates within the underground part of the seedlings was investigated by temporal autoradiography using an imaging plate. Within 1 day, ¹⁴C was transferred from the shoot to the underground part that included roots, mycorrhizae, and the extraradical mycelium; within 3 days, the ¹⁴C in the underground part reached its maximum density. Mycorrhizae and actively growing root tips were large C sinks. Three days after ¹⁴C labelling, counts of ¹⁴C radioactivity in the underground part of the mycorrhizal seedlings were 2.6 times those of nonmycorrhizal seedlings. The mycorrhizae of mycorrhizal plants accumulated 5.2 times the ¹⁴C counts in the short-root tips of nonmycorrhizal plants. ¹⁴C counts in various areas of the extraradical mycelium demonstrated that all ¹⁴C-photosynthate transfer from the host root to the extraradical mycelium occurred within 3 days after ¹⁴C labelling, and that there was only a short lag of <1 day between ¹⁴C accumulation in the basal and distal parts of the mycelium. Although more ¹⁴C accumulated in the distal than in the basal parts, ¹⁴C counts per unit hyphal biomass were similar between the two. These results suggest that ¹⁴C spread rapidly throughout the entire mycelium. Thirteen days after ¹⁴C labelling, we estimated ¹⁴C allocation to extraradical mycelia by taking autoradiographs after removing host roots. About 24% of ¹⁴C counts in the underground part of the mycorrhizal seedlings had been allocated to extraradical mycelia in this system, indicating that the fugal mycelium is an important sink for photosynthates.