Response of ectomycorrhizal and other Pinus sylvestris root-associated fungi to the load of allochthonous material from a great cormorant colony.

Colonies of piscivorous birds nesting in forests bring in loads of allochthonous material in amounts significantly exceeding atmospheric depositions, eventually causing major ecosystem changes. We studied the effect of increasing ornithogenic impact on ectomycorrhizal (EMF) and other root-associated fungi in a Scots pine forest affected by a colony of great cormorants. We evaluated quantitative data of ectomycorrhiza (numbers of root tips and morphotypes) and identified fungal species from pine root tips and from sporocarps collected in three designated study zones: D (zone of active nesting), E (colony margin), and G (pristine forest). Species-bearing sporocarps were absent in zone D, and their number steadily decreased in zone E and was significantly lower than in zone G. Species communities and occurrence frequencies of individual species differed significantly between the zones. Environmental factors, both directly (nutrient addition) and indirectly (changes in vegetation cover), associated with bird activity have significantly influenced fungal communities. We hypothesize that the first signs of increased avian impact on root-associated fungi are the reduced diversity of sporocarps and the low presence and diversity of boletoid fungi in root tips.