Effects of salinity on sawgrass (Cladium jamaicense Crantz) seed germination

Abstract

Sea level rise threatens coastal peatlands globally, as increased salinity can cause peat collapse and formation of brackish ponds, replacing marshes. Sawgrass, Cladium jamaicense Crantz (Cyperaceae), is the charismatic macrophyte that dominates Everglades marshes (Florida, USA). Sawgrass root growth is reduced by salinity pulses of 20 ppt, impacting soil structure and organic input into coastal peats and possibly leading to coastal marsh loss. The potential for regeneration of coastal sawgrass marsh from seeds depends on how salinity affects sawgrass germination. Although adult sawgrass plants can tolerate salinities of 10–20 ppt in the field, the effect of salinity on seed germination is not known. In this study, sawgrass seeds were exposed to salinities of 0, 5, 15, and 25 ppt and observed weekly for germination over seven months (Oct. 2017-Apr. 2018). Twenty-eight percent of seeds in 0 ppt water germinated, while only 4% of seeds in 5 ppt germinated. Seeds in 15 and 25 ppt salt did not germinate. After 3.6 months, four-fifths of the seedling trays at the two higher salinities were transferred to 0 ppt. Beginning 7 weeks after transfer, 6% (15 ppt) and 3% (25 ppt) of transferred seeds germinated, while seeds remaining at the higher salinities did not. These results indicate that sawgrass seeds have greatly reduced or no germination in elevated salinity. If salinities rise in coastal areas, this lack of germination could prevent coastal sawgrass regeneration from seed, negatively affecting coastlines as sea level continues to rise.