Changes in dominance among species in aquatic hyphomycete assemblages do not affect litter decomposition rates

Abstract

Fresh waters are threatened worldwide by water pollution and extraction, changes in riparian vegetation and global warming. Changes in community dominance are expected as an early outcome of anthropogenic stresses, later followed by a reduction in species number and changes in species identity, which might impair ecosystem processes. Here, we addressed the effect of changes in dominance among species in fungal assemblages on the decomposition of alder leaves and associated fungal activity. In laboratory microcosms, we inoculated alder leaf discs with 2 fungal assemblages, each composed of 3 species known to dominate communities during early decomposition (early assemblage) and late decomposition (late assemblage). For each assemblage type, the identity of the dominant species was tentatively manipulated by inoculating the microcosms with distinct proportions of conidia in 4 inocula: an even inoculum and 3 uneven inocula (each dominated by a different species). Over the incubation time, all early assemblages became dominated by the same aquatic hyphomycete species, while manipulation of the number of conidia in the inocula successfully determined the dominant species in late assemblages. Total conidial production and respiration rates differed among early assemblages, but no differences were found in litter decomposition and associated fungal variables among late assemblages. The absence of a relationship between community dominance/identity of the dominant species and community performance/litter mass loss suggests that assemblages, even those composed of a low number of species, have the capacity to buffer changes in processes due to changes in species dominance.