Arch. Hydrobiol. 166 4 467–490 Stuttgart, August 2006 Eucalyptus plantations affect fungal communities associated with leaf-litter decomposition in Iberian streams Verónica Ferreira 1 *, Arturo Elosegi 2 , Vladislav Gulis 1, 3 , Jesús Pozo 2 and Manuel A. S. Graça 1 Universidade de Coimbra With 7 figures and 3 tables Abstract: The replacement of diverse deciduous forests by eucalyptus plantations changes the timing, quality and quantity of litter inputs to streams, which has the potential to affect the activity of decomposers and thus ecosystem functioning. Here, we compared (a) the decomposition rate of alder and oak leaves incubated in decidu- ous and eucalyptus streams in Spain and Portugal, (b) the activity (fungal biomass and sporulation) and diversity (species richness and Pielou’s evenness index) of the asso- ciated fungal communities and (c) changes in N and P content of leaves. Alder and oak leaves decomposed at similar rates in both stream types and countries, with the excep- tion of oak leaves in the Spanish eucalyptus stream, which decomposed faster than in the corresponding deciduous stream or in the Portuguese eucalyptus stream. This dif- ference was attributed to physical fragmentation due to flooding and not to forest cover. Higher nitrogen and phosphorus content and higher fungal biomass and sporula- tion were generally found on leaves from eucalyptus rather than from deciduous streams. The higher fungal activity in eucalyptus streams was attributed to higher wa- ter temperature and benthic organic matter storage. The Spanish eucalyptus stream had higher species richness of aquatic hyphomycetes than the deciduous one (27 vs. 20) while in Portugal the opposite was true (16 vs. 20). Fungal community evenness was significantly higher on alder leaves in eucalyptus than in deciduous streams. The com- munity structure (MDS analysis) discriminated both stream types in Portugal much better than it did in Spain. At least for Portugal, differences between stream types can be explained by higher litter diversity in deciduous than in eucalyptus streams. In 1 Authors’ addresses: Dept. de Zoologia e IMAR-CIC, Universidade de Coimbra, Largo Marquês de Pombal, 3004–517 Coimbra, Portugal. 2 Dept. de Biología Vegetal y Ecología, Fac. de Ciencia y Tecnología, UPV/EHU, Apdo. 644, 48080 Bilbao, Spain. 3 Current address: Dept. of Biological Sciences, University of Alabama, Tuscaloosa, AL 35487, USA. * Corresponding author; e-mail: veronica@ci.uc.pt DOI: 10.1127/0003-9136/2006/0166-0467 0003-9136/06/0166-0467 $ 6.00  2006 E. Schweizerbart’sche Verlagsbuchhandlung, D-70176 Stuttgart