Bacteria are crucial components of ecosystems and play important roles in many ecological processes. Bacterial diversity patterns are always affected by multiple factors such as climatic changes. Elevational gradient has been considered as a natural laboratory for examining the influence of climatic changes on biodiversity patterns. Study of the elevational distribution of bacterial communities is very important in biogeography and can provide basic information on microbial ecology.
The distribution patterns of bacterial communities along elevational gradients and corresponding driving factors of the biodiversity pattern remain unclear in aquatic ecosystems and need to be explored. Contemporary environmental v versus differences in elevation, which factor is more important as a driving force in shaping the bacterial distribution patterns at different depths of the lake sediments along the elevational gradient.
In the present study, sediment samples (three different layers: 0-1, 4-5, and 9-10 cm) were collected from 8 lakes along an elevational gradient from 525 to 4 490 m in Siguniang Mountain region in western China. The recently developed 454 pyrosequencing technique was employed to analyze the bacterial 16S rRNA gene. The relative importance of contemporary environmental heterogeneity and elevational gradient on the bacterial diversity and structure was also assessed.
Results/Conclusions
The most important finding of the present study was that the bacterial alpha diversity (both taxonomic richness and phylogenetic diversity) at different sediment depths decreased monotonically with increasing elevation. The beta diversity (dissimilarity between lakes) increased significantly with the increasing elevation distance. Phylogenetic structure analysis demonstrated that environmental filtering was the most important process structuring the bacterial diversity along the elevational gradient, and its strength increased towards high elevations. Although both elevation and chemical variables including pH and carbon/nitrogen ratio were identified as major factors affecting the bacterial diversity, there was a shift from associations of bacterial communities with elevation and sediment chemistry at the surface sediments, to an association mainly with elevation at the subsurface sediments.
In summary, we observed for the first time a monotonically decreasing elevational pattern in bacterial diversity of freshwater lake sediments, which is mainly driven by elevation associated environmental factors.