HYPHAL TRANSPORT OF N-15-LABELED NITROGEN BY A VESICULAR-ARBUSCULAR MYCORRHIZAL FUNGUS AND ITS EFFECT ON DEPLETION OF INORGANIC SOIL-N

Hyphal transport of nitrogen from a N-15-labelled ammonium source by a VA-mycorrhizal fungus was studied under controlled experimental conditions. Cucumis sativus L. cv. Aminex (Fl hybrid) was grown alone or together with Glomus intraradices Schenck and Smith in containers with a hyphal compartment separated from the rooting medium by a fine nylon mesh. Lateral movement of the applied N-15 towards the roots was minimized by using a nitrification inhibitor (N-serve) and a hyphal buffer compartment. Recovery of N-15 by mycorrhizal and non-mycorrhizal plants was 6 and 0 %, respectively, after a labelling period of 23 days. The corresponding figures, without N-serve added, were 4 and 7 %. A prolongation of the labelling period by 8 days (N-serve applied) resulted in an increase in the N-15 recovery by mycorrhizal plants to 30 % of the applied N-15. Non-mycorrhizal plants contained only traces of N-15. The external hyphae depleted the soil in the hyphal compartment efficiently for inorganic N. In contrast, hyphal compartments of control containers still contained considerable amounts of inorganic N. The N-15 assimilated by the external hyphae in one hyphal compartment was not translocated in significant amounts to the external hyphae in another hyphal compartment. The possible implication of this for inter-plant N transfer by VA hyphal connections is discussed.