Contrasting patterns of diversity of abundant and rare bacterioplankton in freshwater lakes along an elevation gradient

Bacterial communities comprise large numbers of species and normally include a few abundant taxa and many rare taxa. These two subcommunities may have fundamentally different ecological roles, and it is not clear whether their diversity patterns along elevation gradients vary. In this study, we investigated the diversity of bacterioplankton and their subcommunities, i.e., abundant and rare bacterioplankton, in lakes across gradual elevations from 525 m to 4652 m at Siguniang Mountain in western China via the high-throughput sequencing of bacterial 16S rRNA genes. Elevation showed strong influence on bacterioplankton community composition (BCC) and that the dissimilarity of BCC increased with increasing differences in elevation. However, the elevational distance-decay rate of abundant bacterioplankton was higher than that of rare bacterioplankton. Abundant bacterioplankton were more sensitive to changes of environmental factors than rare bacterioplankton. We observed a marginal increase in alpha diversity, estimated as operational taxonomic unit richness and phylogenetic diversity, of overall bacterioplankton with increasing elevation. The alpha diversity of abundant bacterioplankton decreased monotonically with elevation; in contrast, the alpha diversity of rare bacterioplankton increased monotonically with elevation. Null model tests indicated that environmental filtering played a dominant role in overall bacterioplankton community assembly along the elevation gradient, while there was decreased contribution of environmental selection to rare bacterioplankton in smaller lakes at higher elevation. Our results revealed that abundant bacterioplankton followed the general elevation diversity theory commonly found for plants and animals in freshwater lakes, whereas rare bacterioplankton did not follow this tenet.