Reduced15N-nitrogen Transport Through Arbuscular Mycorrhizal Hyphae to Triticum aestivum L. Supplied with Ammonium vs. Nitrate Nutrition

This study compared the influence of \({ NH }₄⁺\) or \({ NO }₃⁻\) nutrition on the contribution of extraradical hyphae of the arbuscular mycorrhizal fungus Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe (BEG 107) to \({ NH }₄⁺\) or \({ NO }₃⁻\) uptake by Triticum aestivum L. ‘Hano’ (summer wheat) with sufficient or insufficient N supply in semi-hydroponic culture. Roots and root-distant hyphae were spatially separated in compartmentalized pots. Although \({ NH }₄⁺\) -fed plants supplied with sufficient N had higher N concentrations than their \({ NO }₃⁻\) -fed counterparts, this did not favourably affect colonization rates, hyphal length densities or 15 N amounts transported via hyphae to the plants. Ammonium supply did not result in higher P or reduced carbohydrate concentrations in the plants, so these factors could not explain the reduced hyphal lengths. It was concluded that the effect of \({ NH }₄⁺\) supply on hyphal length may be related to the reduced root growth and/or a direct effect of \({ NH }₄⁺\) on hyphal growth. Plant N deficiency reduced the percentage root length colonized, hyphal length, total 15 N uptake by hyphae and dry weight of both \({ NO }₃⁻\) - and \({ NH }₄⁺\) -fed mycorrhizal plants. This was more obvious for \({ NO }₃⁻\) -fed plants because plant biomass and hyphal lengths of \({ NH }₄⁺\) -fed plants were relatively low in mycorrhizal plants irrespective of the N concentration supplied.