Phragmites australis is a frequent component of temperate inland and coastal wetlands. Ongoing environmental changes have resulted in the decline of this species in many areas and invasive expansion in others. In south-eastern Australia, the Gippsland Lakes system (GLS) is an extensive coastal waterway system that has experienced increasing salinization since the late 19th century. Increasing salinity is thought to have contributed to the loss of fringing Phragmites reed beds leading to increased shoreline erosion. A major goal of restoration in this waterway is to address the effect of salinity by planting a genetically-diverse range of salt-tolerant Phragmites lineages. This has prompted an interest in examining the genetic structure of Phragmites across the GLS and the variation in salinity tolerance among lineages.
We used microsatellites to investigate population structure of Phragmites across the GLS and transcriptomics to identify differential gene expression in response to salinity among Phragmites clones. We used an RNA-Seq approach to identify culm-expressed genes in Phragmites associated with exposure to saline water. Six clonal lineages were obtained from areas of low or high salinity across the GLS and grown in pot trials. Paired-samples of the clones from each site were irrigated with either fresh-, or highly saline water. We sequenced transcriptomes from the culms of each of these twelve samples allowing an analysis of differential gene expression.
Among key findings, Phragmites formed a single genetic cluster across the GLS consistent with high levels of genetic connectivity facilitated by wind dispersal. Several genes were differentially expressed in clones from highly saline sites when irrigated with saline water relative to clones from low salinity sites. Our data suggest local adaptation of certain clones to salinity and provide scope to develop restoration protocols designed to address the impacts of increasing salinity.