Eucalyptus spp. leaf traits determine litter processing by fungi and invertebrates.
Eucalyptus is one of the most cultivated genera globally. Conversion of native forests into Eucalyptus spp. monocultures leads to species-specific changes in the quality of the litter that contributes to the structure and function of allochthonous-based aquatic systems. We used a microcosm approach to compare the relative importance of structural and chemical leaf trait variability among congeneric exotic Eucalyptus species (E. camaldulensis, E. globulus, E. grandis, and E. nitens) and two Portuguese native species-alder (Alnus glutinosa) and oak (Quercus robur)-on microbial-mediated decomposition and invertebrate shredder (Trichoptera: Sericostoma vittatum) consumption. Structural leaf traits, rather than chemical characteristics, appeared to be the main determinants of leaf-processing dynamics. Differences between the exotic species were mainly determined by the persistence (E. globulus, E. grandis, and E. nitens) or detachment (E. camaldulensis) of the cuticular barrier soon after immersion. Detachment favoured an earlier and higher level of fungal colonisation, as well as a higher mass loss. Sericostoma vittatum exhibited higher consumption rates when fed by the nitrogen-rich and softer alder leaves, E. camaldulensis, and oak. Consistently lower consumption rates were observed in the other three Eucalyptus species (64-77% lower than E. camaldulensis). Leaf litter from these species was colonised by a lower number of fungal species and was dominated by Flagellospora curta. Results suggest that streams adjacent to E. camaldulensis monocultures receive a continuous supply of easily degradable organic matter throughout the year. The potential effect of subsidies from this species in alleviating the general negative impacts of Eucalyptus plantations on native bordered aquatic systems remains to be evaluated.