Spatiotemporal distribution of an ectomycorrhizal community in an oligotrophic Swedish Picea abies forest subjected to experimental nitrogen addition:: above- and below-ground views

The effects of enhanced nitrogen availability in formerly nitrogen-limited forest ecosystems on the species diversity of sporocarps and mycorrhizas of ectomycorrhizal (EM) fungi were studied in a nitrogen addition experiment at Gardsjon, an oligotrophic Norway spruce forest in SW Sweden. The experiments were performed by comparing plots that had received additions of nitrogen-enriched water (35 kg N ha(-1) annually since 1991) by means of sprinkling system with plots only receiving ambient (about 12 kg N ha(-1) per year) nitrogen deposition. The above-ground EM sporocarp production was recorded in 1992-1996; the number of mycorrhizas and their gross morphotype differentiation were registered in 1992-1995, and the mycobionts of randomly selected mycorrhizas were identified in detail by ITS-RFLP analyses in 1994. The addition of nitrogen did not affect the species richness or diversity of below-ground EM fungal species. In total, 50 RFLP-taxa were distinguished, of which 15 occurred in both treatments and 29 occurred only in single plots. However, the species richness and diversity of sporocarps of EM species were lower in the nitrogen-treated stand. Spatial distribution patterns of below-ground EM fungal taxa were assessed at various scales, from centimetres to tens of meters. Aggregations of mycorrhizal morphotypes were apparent on the centimetre scale, whereas no apparent spatial pattern could be discerned in the below-ground community on the meter scale. in accordance with the survey of below-ground taxa, the sporocarp analysis revealed that most species were rare, and only a few were widely distributed. The number of mycorrhizas per unit area differed among years, whereas the relative abundance of Cenococcum geophilum and Piloderma croceum appeared to be stable. (C) 2000 Elsevier Science B.V. All rights reserved.