4.1 Different diversity patterns of abundant and rare bacteria
In this study, we found that bacterial α-diversity was significantly
higher in the rare subcommunity than in the abundant subcommunity (Fig.
S2). This result supports the notion that rare taxa play the role of
“seed bank” in maintaining microbial diversity (Lynch and Neufeld,
2015; Shade et al., 2014). Our results also showed that the rare
subcommunity displayed higher β-diversity than the abundant subcommunity
in fluvial sediments (Fig. 2). This finding suggests that
differentiation of the rare subcommunity along environmental gradients
is higher than the abundant subcommunity. Variations in β-diversity
generally depend on the interaction of species traits (e.g., ability to
disperse and niche width) and characteristics of the environmental
conditions (e.g., environmental heterogeneity and topographic
complexity) (Maloufi et al., 2016; McKnight et al., 2007). In virtue of
the rare and abundant subcommunities being subjected to the same
environmental conditions, the higher β-diversity of the rare
subcommunity may partly be attributable to the potential of some rare
taxa could be actively growing or waking up from dormancy and present in
the currently active community (Jiao et al., 2017; Pedrós-Alió, 2012).