| A series of studies quantifying the role of the interactive effects of salinity and soil drying on the survival, growth, nutrient uptake, and physiology of Spartina alterniflora were conducted in a climate controlled greenhouse. The experiments consisted of multiple levels of salinity (3-5 ppt, L; 15-20 ppt, M; and 35-38 ppt, H) as well as several dynamic water levels: drought (water level maintained at 20 cm below the soil surface at high tide, D), intermediate soil drying (water level maintained between 20 cm below the soil surface at low tide and 10 cm below the soil surface at high tide, I), and flooding (water level maintained 3-5 cm above the soil surface at high tide and 10 cm below the soil surface at low tide, F). Plant survival, gas exchange, growth responses, and nutrient uptake were measured along with soil conditions of redox potential and water potential. Contrary to expectations, the interactive effects of salinity and soil drying were not strictly additive on plant survival, growth, and physiology. Significant decreases were noted in plant gas exchange and growth in response to increases in salinity and soil drying. In addition, significant decreases were seen in all nutrients in response to increases in salinity and/or soil drying. Survival was 100% for all flooded treatments while increased salinity combined with soil drying decreased survival in medium salt/drought plants (MD) and high salt/intermediate soil drying (HI) treatments. The lowest survival rate was seen in the high salt/drought treatment (HD) at 29%. Therefore, it appears that drought may magnify the adverse effects of salinity on plant function. Consequently, these studies demonstrate that combined effects of high salinity and drought proved to be detrimental to S. alterniflora. It also appears that the critical time for recovery from the combined effects of increased salinity and soil drying may greatly diminish after two weeks from the onset of stress conditions. Therefore, if salinity continues to increase along the Mississippi River Deltaic Plain, marshes dominated by S. alterniflora may be more susceptible to short-term drought and likewise large-scale marsh browning. |
