Discussion
Plant responses to salt stress
Salinities were lower than indicated by the initial treatment additions. In particular the Spartina treatment had much lower salinities across all treatment levels. This is thought to be a result of the active excretion of salt via the leaf salt glands. The leaf canopy was rinse 1-2x per week to remove salts as they built up and was then lost from the treatment over time. While the salinity gradient that resulted by the end of the experiment was not as large as originally planned, there are measurable changes in all three species that occurred as salinity increased in the three treatment groups (fresh, brackish, marine). A lack of marine data in Spartina (loss of salts) and Schoenoplectus (intolerant of higher salinity) means that Juncus was the only species where the effects of this higher salinity treatment could be observed. In that species, morphological changes were evident, primarily as reduced leaf length and width, biomass differences were evident in all three fractions (AL, AD, BG) but the total biomass was dominated by the BG fraction, as well as photosynthetic parameters related to chl flr that were happening independent of the chl content. These data suggest that a more complete set of treatments would potentially yield more comprehensive data on species x salinity responses, much as the original experimental design had intended to do. Nonetheless both morphological changes were evident, primarily as reduced leaf length and width, as well as photosynthetic parameters related to chlorophyll fluorescence that were happening independent of the chlorophyll content.
Rhizosphere responses
Sediment associated microbiomes in the salinity treatments for the three plant species showed both salt range and species-specific differences in diversity and community composition.
Venn diagrams of the diversity of the sediment microbiome (genus level) by salinity and species.
Ordination plot of OTU's in the sediment microbiome by salinity and species.
Network analysis of the diversity of the sediment microbiome by salinity for all samples.