Effect of seawater salinity stress on Sporobolus pungens (Schreb.) Kunth, a halophytic grass of the mediterranean embryonic dunes

Sporobolus pungens (Schreb.) Kunth is a perennial rhizomatous grass which develops at several coastal habitats, being relevant in the embryonic dune communities. Considering its importance for dune ecosystem and its fragile situation in the face of changes in sea level derived from global warming, the present study aimed to evaluate S. pungens response to increased salinity. One-year-old plants were exposed to different seawater (SW) dilutions (None, 1/16SW, 1/8SW, 1/4SW, 1/2 W and Full-SW). Gas exchange measurements and oxidative stress biomarkers were determined after two months of treatment. Stress conditions were maintained until flowering finished in order to assess the potential effects on the reproductive effort. Strong delay and inhibition of flowering were observed at low salinity levels and full inhibition for further treatments. Gas exchange measurements showed little effect until 1/8SW and a decreased assimilation rate due to mainly stomatal limitations at 1/4SW. Further decreases at higher salinity levels were related to both stomatal and metabolic limitations. As salinity increased, there was a progressive increase in the activity of glutathione peroxidase and glutathione reductase, while catalase activity remained stable. Superoxide dismutase did not vary except for Full-SW, where the activity significantly decreased. The levels of malondialdehyde, a marker of lipid peroxidation, remained unchanged and only increased in Full-SW level. In addition, the concentration of osmolytes, proline and soluble sugars, increased progressively with increasing salinity. In conclusion, S. pungens showed strong tolerance to salinity, through physiological adjustments at low levels of salinity, and activating glutathione-dependent enzymes at the highest concentrations. Evidence of oxidative damage was only observed after Full-SW exposure, although no death rate was recorded.