Hyphal transport of15N‐labelled nitrogen by a vesicular—arbuscular mycorrhizal fungus and its effect on depletion of inorganic soil N

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Abstract
SUMMARY: Hyphal transport of nitrogen from a15N‐labelled ammonium source by a VA‐mycorrhizal fungus was studied under controlled experimental conditions.Cucumis sativusL. cv. Aminex (F1 hybrid) was grown alone or together withGlomus intraradicesSchenck and Smith in containers with a hyphal compartment separated from the rooting medium by a fine nylon mesh. Lateral movement of the applied15N towards the roots was minimized by using a nitrification inhibitor (N‐serve) and a hyphal buffer compartment. Recovery of15N 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 the15N recovery by mycorrhizal plants to 30% of the applied15N. Non‐mycorrhizal plants contained only traces of15N. 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. The15N 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.