Uptake and transport of organic and inorganic nitrogen by arbuscular mycorrhizal fungi

New information on N uptake and transport of inorganic and organic N in arb uscular mycorrhizal fungi is reviewed here. Hyphae of the arbuscular mycorr hizal fungus Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe (BEG 107) w ere shown to transport N supplied as N-15-Gly to wheat plants after a 48 h labelling period in semi-hydroponic (Perlite), non-sterile, compartmentalis ed pot cultures. Of the N-15 supplied to hyphae in pot cultures over 48 h, 0.2 and 6% was transported to plants supplied with insufficient N or suffic ient N, respectively. The increased N-15 uptake at the higher N supply was related to the higher hyphal length density at the higher N supply. These f indings were supported by results from in vitro and monoxenic studies. Exci sed hyphae from four Glomus isolates (BEG 84, 107, 108 and 110) acquired N from both inorganic ((NH4NO3)-N-15-N-15, (NO3-)-N-15 or (NH4+)-N-15) and or ganic (N-15-Gly and N-15-Glu, except in BEG 84 where amino acid uptake was not tested) sources in vitro during short-term experiments. Confirming thes e studies under sterile conditions where no bacterial mineralisation of org anic N occurred, monoxenic cultures of Glomus intraradices Schenk and Smith were shown to transport N from organic sources (N-15-Gly and N-15-Glu) to Ri T-DNA transformed, AM-colonised carrot roots in a long-term experiment. The higher N uptake (also from organic N) by isolates from nutrient poor si tes (BEG 108 and 110) compared to that from a conventional agricultural fie ld implied that ecotypic differences occur. Although the arbuscular mycorrh izal isolates used contributed to the acquisition of N from both inorganic and organic sources by the host plants/roots used, this was not enough to i ncrease the N nutritional status of the mycorrhizal compared to non-mycorrh izal hosts.