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.