Changes in dominance among species in aquatic hyphomycete assemblages do not affect litter decomposition rates
Résumé
Fresh waters are threatened worldwide by water pollution and extraction, changes in ripar- ian vegetation and global warming. Changes in com- munity dominance are expected as an early outcome of anthropogenic stresses, later followed by a reduc- tion in species number and changes in species iden- tity, which might impair ecosystem processes. Here, we addressed the effect of changes in dominance among species in fungal assemblages on the decom- position of alder leaves and associated fungal activ- ity. 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 assem- blage type, the identity of the dominant species was tentatively manipulated by inoculating the micro- cosms with distinct proportions of conidia in 4 inoc- ula: an even inoculum and 3 uneven inocula (each dominated by a different species). Over the incuba- tion 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 respira- tion 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.
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