Plasticity of N:P ratios in laboratory and field populations of Trichodesmium spp.

• Published in: Aquatic Microbial Ecology
• Main Authors: Krauk, Jamie M., Villareal, Tracy A., Sohm, Jill A., Montoya, Joseph P., Capone, Douglas G.
• Other Authors: University of Maryland Center for Environmental Sciences. Chesapeake Biological Laboratory, University of Texas at Austin. Marine Science Institute, USC Wrigley Institute for Environmental Studies, University of Southern California. Dept. of Biological Sciences, Georgia Institute of Technology. School of Biology
• Format: Article in Journal/Newspaper
• Language: English
• Published: Georgia Institute of Technology 2006
• Subjects: Trichodesmium; N:P ratio; Nitrogen fixation; Diazotroph; Cyanobacteria; North Atlantic
• Online Access: http://hdl.handle.net/1853/43090; https://doi.org/10.3354/ame042243

© 2006 Inter-Research. DOI:10.3354/ame042243 We followed changes in N:P ratios in batch cultures of the planktonic marine cyanobacterium Trichodesmium (IMS 101) grown in 2 different media and in field populations from 4 different oceanic regions. Cultures grown on low P media showed a rapid rise in N:P ratio upon depletion of phosphate. Ratios exceeding 125 were reached in 1 experiment before attaining stationary phase. A transect across the North Atlantic Ocean along 32°N showed a monotonic decrease in the N:P ratio of field collected colonies, dropping from about 60:1 on the western side of the basin to about 30:1 on the eastern side. A second cruise sampled colonies and surface slicks in waters along the north coast of Australia, where ratios of N:P were generally lower than in the North Atlantic, ranging from 11:1 to 47:1 with an average of 22:1. A comparison of rising and sinking colonies collected at 8 stations in the Gulf of Mexico shows a higher mean N:P ratio among sinking colonies than floating colonies. Overall, the average N:P in the Gulf of Mexico was about 68:1. N:P ratios of Trichodesmium around the Hawaiian Islands were very consistent between 2 consecutive years of sampling, with an average colony N:P for both years of about 38:1. Our research demonstrates high variability in the cellular N:P in Trichodesmium both in the laboratory and in the field. Trichodesmium N:P ratio may provide an index to the relative severity of P limitation in these diazotrophs. Geochemical and ecological modeling efforts which rely on using the N:P ratio of diazotrophs in deriving nitrogen fixation rates should account for the variability of these ratios in situ.