The river shapes the genetic diversity of common reed in the Yellow River Delta via hydrochory dispersal and habitat selection.

Understanding the driving mechanisms of local genetic diversity is a fundamental challenge under the global environmental changes. Rivers provide an excellent study system to demonstrate the effects of hydrochory dispersal and habitat selection on genetic diversity of riparian flora. In this study, we focused on the genetic variation of common reed (Phragmites australis) in the Yellow River Delta, China. Firstly, samples were collected in the Yellow River Delta, its neighboring wetland and its upstream plain. The genetic variation of P. australis was investigated using two chloroplast DNA fragments and eleven nuclear microsatellites. The findings showed that the genetic variation of P. australis in the Yellow River Delta belonged to two distinct lineages (haplotype O and haplotype P), which were similar to the upstream, and to the neighboring populations, respectively. Moreover, the genetic results suggested the potential dispersal of haplotype O from upstream to downstream. Secondly, we surveyed the plant functional traits of common reed from the Yellow River Delta in the field and in the common garden. The results showed significant differences between riverine and non-riverine populations in plant functional traits (e.g. specific leaf area and leaf length), haplotype composition and genetic clustering, which implied natural selection by habitat conditions. Lastly, we re-analyzed the plant performance data from a salt manipulation experiment with different haplotypes, and the results supported that salinity is a significant selective stressor on P. australis lineages in the Yellow River Delta. Our study highlights the significance of hydrochory dispersal and habitat selection in the river effects on genetic diversity of riparian flora, and provides important information for biodiversity conservation and wetland management in the Yellow River Delta.