Two low-lying coastal grassland species differ in mechanistic response to saline flooding stress

摘要

Coastal wetlands and low-lying coastal grasslands are increasingly susceptible to salt water intrusion (SWI) influenced by storm surge and sea-level rise. Our aim was to understand physiological and growth responses of dominant coastal grassland species, Spartina patens (Ait.) Muhl. (Poaceae) and Fimbristylis castanea (Michx.) Vahl. (Cyperaceae), to increased saline flooding as expected with sea-level rise or saltwater intrusion. We hypothesized that S. patens would exhibit greater resistance to salt stress due to wider distribution. Both species were subjected to saltwater flooding at 0, 5, 10, and 20 ppt (parts per thousand) for 16 weeks. Physiological, morphological, and biochemical responses were measured at the end of the experiment. Biomass and tissue chlorides were quantified above- and belowground. Physiology was minimally affected by increased saltwater. Relative growth rate and aboveground biomass were reduced in both species at 20 ppt. Both species maintained belowground biomass, with increased root and leaf tissue chlorides as salinity increased. The results did not support our hypothesis and found that both species are impacted by saltwater flooding, but S. patens exhibited more signs of stress at 20 ppt. However, both species exhibited tolerance to long-term salt stress through different mechanisms. Spartina patens excretes salts and allocates resources belowground, whereas F. castanea maintains root:shoot and exhibits higher relative water content. Maintaining or allocating biomass belowground with increasing salinity may be important in future sea-level rise and saltwater intrusion scenarios as low-lying coastal systems are at higher risk of erosion. Reduction in plant size (aboveground biomass) may impact function of coastal grasslands.