The effects of abiotic and biotic factors on taxonomic and phylogenetic diversity of stream epilithic bacteria around Qiandao Lake

Stream bacterial communities are shaped by a combination of local and regional processes, such as environmental filtering, biotic interactions and dispersal, but biotic interactions have received comparatively less attention. Here, we investigated stream bacterial alpha and beta diversity within taxonomic and phylogenetic contexts around Qiandao Lake in China. We further examined abiotic and biotic factors on bacterial communities by explicitly considering biotic variables including macroinvertebrate species richness, total cover of periphyton and submerged macrophytes. For alpha and beta diversity, there were consistently high correlations between taxonomic and observed phylogenetic metrics. Taxonomic and phylogenetic diversity could be explained by abiotic and biotic variables, though the former showed a stronger influence. Using a null model to break down the association between species phylogeny and co-occurrence, we found non-significant correlations for alpha and beta diversity between taxonomic and phylogenetic diversity, that is, the standardized effect size of phylogenetic diversity (ses.PD) or Unifrac dissimilarity (ses.Unifrac). Variations in taxonomic and phylogenetic diversity at both alpha and beta levels were mainly explained by pure effect of abiotic variables. Biotic variables, such as macroinvertebrate species richness and total cover of periphyton, significantly explained the variations in ses.PD and ses.Unifrac by 19.4% and 18.9%, respectively. Our findings provide an evidence that biotic variables play a non-negligible role in structuring bacterial communities and help to better understand the potential role of biological interactions across trophic levels in streams.