Abstract
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.
Highlights
Fresh waters are presently among the most endangered ecosystems in the world, and this situation is expected to deteriorate in the near future, in part as a result of increases in demands for fresh water and in loads of nutrients and pollutants into aquatic systems from a growing human populationAquat Microb Ecol 66: 1–11, 2012(MEA 2005)
Half of the microcosms were inoculated with an assemblage composed of early colonizer species (LETE, Tetrachaetum elegans Ingold (THEL) and Tricladium chaetocladium Ingold (TRCH)), while the other half were inoculated with an assemblage composed of late colonizer species (ARTE, CLAQ and Tetracladium marchalianum Ingold (TEMA)) (Gessner et al 1993, Nikolcheva et al 2003)
Sporulation rates associated with alder discs at Day 28 varied between 119 and 404 conidia mg−1 dry mass (DM) d−1 but were not significantly affected by dominance treatment (Fig. 2B)
Summary
Fresh waters are presently among the most endangered ecosystems in the world, and this situation is expected to deteriorate in the near future, in part as a result of increases in demands for fresh water and in loads of nutrients and pollutants into aquatic systems from a growing human population. The relationship between species evenness and ecosystem processes has been addressed only recently (Wilsey & Potvin 2000, Dangles & Malmqvist 2004, McKie et al 2008, Gonçalves & Canhoto 2009, Swan et al 2009, Ward et al 2010), and its relevance for microbial communities has not yet been examined In this experiment, we assessed whether changes in the identity of the dominant species in aquatic hyphomycete assemblages would affect decomposition rates of alder leaves and associated fungal activity. Ferreira & Chauvet: Identity of fungal species and decomposition occur well before there is species loss due to anthropogenic activities
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