Andrew F. S. Taylor

• Soil abiotic factors are considered to be important in determining the distribution of ectomycorrhizal (ECM) fungal species; however, there are few field data to support this. Here, we relate ECM species distributions to changes in soil chemistry along a short (90-m), natural nutrient gradient. • The ECM community was characterized, using morphological and molecular techniques, in soil samples collected at 10-m intervals. • There were pronounced changes in ECM fungal community structure along the transect, with many taxa showing discrete distributions. Although there was a change of host from Pinus to Picea along the gradient, host-specific fungi did not account for the observed change in community structure. Ordination analyses showed that community structure was strongly correlated with soil characteristics, in particular extractable ammonium and base saturation. However, autocorrelation among soil parameters makes it difficult to isolate the effects of individual parameters. • The distinctive changes in soil and vegetation along the transect used in this study provided an exceptional opportunity to examine the local-scale impact of natural spatial heterogeneity on an ECM fungal community.

• While it is accepted that many ectomycorrhizal fungi can assimilate organic substrates and facilitate transfer of their elemental components to plants, the fate of the carbon contained in these materials remains uncertain. Here we investigate the compartmentation of carbon and nitrogen in ectomycorrhizal seedlings of Pinus sylvestris fed with double-labelled (¹⁵N and ¹³C) glycine as their sole N source. • Using isotope ratio mass spectrometry, the quantities of N and C derived from this glycine were determined in sequentially harvested samples of mycorrhizas, roots and shoots. • Whereas considerable quantities of ¹⁵N were observed in the mycorrhizal tips, roots and shoots, comparable amounts of ¹³C were observed only in mycorrhizal tips and roots. • It is clearly important to resolve the role of compound specificity as a factor determining the extent of amino-acid C transfer from roots to shoots. However, from the standpoint of the C budget of the whole plant, wherever heterotrophically acquired C is available as an energy source it will reduce demands on photosynthetically fixed sources of the element.

• The natural abundance of 13C (δ13C) and 15N (δ15N) of saprotrophic and ectomycorrhizal (ECM) fungi has been investigated on a number of occasion...