We examined the effect of nitrogen on sporulation of arbuscular mycorrhizal (AM) fungi colonizing gramineous plant species growing in a volcanic deposit with a nitrogen deficit. Five gramineous species (Saccharum spontaneum, Rhynchelytrum repens, Miscanthus sinensis, Paspalum notatum, and Eragrostis curvula) growing in a volcanic deposit on Mount Fugendake, Japan, were inoculated with the AM fungus Glomus etunicatum with or without the application of nitrate nitrogen (20 mg N kg soil-1). The AM dependent species (M. sinensis and P. notatum) which showed growth response to the inoculation increased sporulation with nitrogen addition. However, the species that did not depend on AM for their growth (S. spontaneum and E. curvula) showed decreased or non-increased sporulation with nitrogen application. This trend was also found for Glomus etunicatum in a dual-inoculation experiment with Glomus etunicatum and Gigaspora margarita. These indicate that the effect of nitrogen on the sporulation of AM fungi differed among gramineous species and that in some species nitrogen may suppress the sporulation.
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