Print PageIncreasing atmospheric CO2 is affecting salt marsh plant communities directly and indirectly with rising temperatures, fluctuations in salinity, and more frequent flooding. Along the Atlantic and Gulf coasts, Schoenoplectus americanus is a common clonal C3 sedge whose productivity is sensitive to CO2, salinity, and sea level. Previous studies have established genetic differences among geographically isolated populations of S. americanus. In addition, there is also genetic variation within historic populations resurrected from seeds in stratified marsh cores. We hypothesized that these differences could translate into ecotypic variation in functional and physiological traits among populations. We conducted a 5-month greenhouse experiment to investigate plant productivity and fitness over space and time in S. americanus populations under salt stress. Populations of S. americanus from Maryland, New Jersey, Louisiana, Texas, and historical Maryland (c. 1910) were grown in fresh (<3ppt NaCl) and brackish (15ppt NaCl) water treatments. Productivity and fitness measurements included growth rates, LICOR 6400XTR physiological measurements, and dry biomass.
Results/Conclusions
There is a significant interaction between salinity levels, population, and genotype when plants are exposed to low levels of CO2 (200 ppm), resulting in differences in photosynthetic rate (p=0.03397). Compared to modern populations, the historical population appears to perform photosynthesis more efficiently in high salinity with a mean of 4.77 mmolCO2m-2s-1. Similarly, when plants are exposed to levels of ambient CO2 (400 ppm), there is a significant interaction between salinity levels, population, and genotype, also resulting in differences in photosynthetic rate (p=0.02644). These findings, along with observed significant differences in biomass and growth rates, suggest evolutionary trends in photosynthetic capacity accompanying rises in atmospheric CO2. This could have an influence on marsh carbon assimilation and accretion over time.
