The impact of eucalypt on the leaf-associated aquatic hyphomycetes in Spanish streams

Aquatic hyphomycete assemblages on decomposing leaf litter of the exotic species Eucalyptus globulus Labill. were compared with those on the native riparian species Alnus gluti~zosa(L.) Gaertn. in three low-order streams of the Agiiera watershed (Basque Country - Cantabria, Spain). These streams contrast by the importance of eucalypt in the riparian vegetation and by the nutrient contents in the water. Neither the total conidial production nor the number of fungal species differed between the two leaf species in any of the streams. Fungal colonization of eucalypt leaves appeared to be delayed by about 2 weeks, probably owing to their high content in inhibitory constituents. While Flagellospora curvula Ingold largely dominated pioneer assemblages on both leaf species, the second most important species, Lunulospora curvula Ingold, exhibited a preference for eucalypt. In the stream surrounded by eucalypt, the fungal diversity was surprisingly lower on eucalypt than on alder. In the stream with higher orthophosphate concentrations, the conidial production was similarly increased on both leaf species. The present data together with recent results from a similar investigation in Portugal suggest a minor impact of eucalypt on the activity and diversity of aquatic hyphomycete leaf-associated assemblages in southern European streams.