Summary: The arbuscular mycorrhizal (AM) fungus Glomus intraradices Schenck and Smith was grown in symbiosis with Cucumis sativus L. ev. Aminex (Fl hybrid) in mesh bags surrounded by a sand‐filled hyphal compartment (HC), allowing only the fungal hyphae to protrude into the HC. The hyphae in the HC were supplied with ¹⁵N‐labelled NH₄⁺ or NO₃⁻ after 60 d (expt 1). Following a 48 h labelling period, the sand was removed from the HC and the hyphae extracted. In another experiment (expt 2), the hyphae were extracted from the sand before being incubated in vitro in a nutrient solution containing ¹⁵N‐labelled NH₄⁺ for 15 h. The hyphal material was incubated in a 0 or 2.5 mM solution of the GOGAT‐inhibitor albizzine prior to labelling. In both experiments the hyphal content of free amino acids and fatty acids were measured as well as the ammo acid ^l5N enrichment.Asparagine was the hyphal amino acid measured in highest concentration followed by glutamine, glutamate, aspartate and alanine. Ornithine, serine and glycine were detected in lower concentrations, but γ‐aminobutyric acid and citrulline were not detectable. This pattern was the same in both experiments and was unaffected by the type of N applied to the hyphae or by preincubation with albizzine, although the amino‐acid concentration decreased considerably in expt 2 compared with expt 1. Both NH₄⁺‐N and NO₃⁻‐N were assimilated into amino acids but the levels of ^l0N enrichment following application of NO₃⁻ were much lower than those following application of NH₄⁺ indicating that the latter was more readily assimilated. Albizzine decreased the hyphal amino acid concentration by c. 30% (without affecting the ¹⁵N enrichment of the individual amino acids) indicating that the AM‐fungal hyphae might possess a GS‐GOGAT enzyme system for assimilation of inorganic N. The fatty‐acid profiles (especially phospholipid fatty acids 16: 1ω5 and 20:5) obtained from the hyphae of G. intraradices showed that contamination of the samples by fungi other than G. intraradices and bacteria was insignificant, and confirmed the usefulness of specific fatty‐acid measurement to estimate soil AM‐fungal content.

Nanotechnology should produce numerous new materials in the coming years. Because of the novel design of nanomaterials with new physicochemical characteristics, their potential adverse impact on the environment and human health must be addressed. In the present study, agglomerates of pristine C₆₀ fullerenes (50 nm to μm‐size) were applied to soil at 0, 5, 25, and 50 mg/kg dry soil to assess their effect on the soil microbiota by measuring total respiration; biomass, number, and diversity of bacteria; and total number and diversity of protozoans during 14 d. Respiration and microbial biomass were unaffected by the fullerenes at any time, whereas the number of fast‐growing bacteria was decreased by three‐ to fourfold just after incorporation of the nanomaterial. Protozoans seemed not to be very sensitive to C₆₀, because their number decreased only slightly in the beginning of the experiment. With polymerase chain reaction and denaturing gradient gel electrophoresis analysis of eubacteria and kinetoplastids from the soil, however, a difference between the fullerene treatments and nonamended controls was demonstrated. The fullerenes did not induce more than 20 to 30% of relative dissimilarity (with both bacteria and protozoans) between treatments, but this effect was persistent throughout the experiment. It therefore is recommended that fullerene nanomaterial not be spread deliberately in the environment and that their ecotoxicology be further clarified.