Natural isotopic composition of carbon (d13C) correlates with colony size in the planktonic cyanobacterium Gloeotrichia echinulata

Vuorio, Kristiina, Markus Meili, Jouko Sarvala

Limnol. Oceanogr., 54(3), 2009, 925-929 | DOI: 10.4319/lo.2009.54.3.0925

ABSTRACT: To assess variability in carbon isotope signatures (δ13C) between and within populations under natural conditions, with a particular emphasis on colony size, we repeatedly collected planktonic colonies of a freshwater cyanobacterium Gloeotrichia echinulata in two lakes, Pyhäjärvi (southwest Finland) and Erken (southeast Sweden). Despite substantial differences in the average δ13C signature of Gloeotrichia between lakes (-6.9% in Pyhäjärvi and -20.7% in Erken), a similar, systematic increase in δ13C with colony size was observed in both lakes (of 2-3% in Pyhäjärvi and 3-5% in Erken). This suggests declining isotope fractionation with increasing colony size, probably related to diffusion limitation of carbon availability. Temporal variation explained a minor fraction of total subsample variability (range δ13C ~4% in Pyhäjärvi and ~6% in Erken). Isotopic 13C fractionation in Gloeotrichia was likely affected both by carbon source and by colony size.

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