Wednesday, August 5, 2009
Exhibit Hall NE & SE, Albuquerque Convention Center
Paul Cuomo, Robert Fisher and Donald Young, Biology, Virginia Commonwealth University, Richmond, VA
Background/Question/Methods Terrestrial primary production in coastal ecosystems, specifically barrier islands, is usually limited by available N in the predominately sandy soils. Among the woody species common on barrier islands, those that form symbiotic relationships with N-fixing bacteria are the most successful. Additional N input may occur from free-living N-fixing bacteria. Anabaena species found in almost every environment, can fix N in the absence of available N. Major inputs of salt on barrier islands include sea spray, and overwash events. Salinity can also lead to discrete distribution patterns of cyanobacteria in soils and in different water sources, e.g. freshwater ponds. Our objective was to determine the effect of salinity on growth and N-fixing ability of Anabaena. We also determined if cyanobacteria were present and could produce sufficient N to warrant inclusion in N-budgets for barrier islands. Soil and water samples from freshwater ponds located on Hog Island, Virginia, were tested for salinity and presence of cyanobacteria. Anabaena cultures were grown in different salinities to test for N-fixation rates. Gas chromotography was used to test N fixation and spectrophotometric measurements were used to test growth and development.
Results/Conclusions At salinity levels lower than 9 ppt Anabaena grew rapidly. Maximum nitrogenase activity, 7.37 mm, occurred in 3 ppt at growth day 7. No nitrogenase activity was detectable at salinities of 15 ppt throughout the 16 day growing period. Differences in nitrogenase activity suggest that salinity could impact cyanobacteria ability to fix N. Hetercyst (site of N-fixation) frequency also showed an increase in salinities between 1.5-4.5 ppt, which could explain the increase in nitrogenase activity. Within the context of spatial variations in salinity on Hog Island, cyanobacteria could have a significant influence on barrier island N-budgets.
