Diel variability in the elemental composition of the marine cyanobacterium Synechococcus

Journal of Plankton Research plankt.oxfordjournals.org J. Plankton Res. (2016) 38(4): 1052–1061. First published online January 18, 2016 doi:10.1093/plankt/fbv120 Contribution to the Themed Section: Scaling from individual p lankton to marine ecosystems Diel variability in the elemental composition of the marine cyanobacterium Synechococcus JOHANN S. LOPEZ 1 , NATHAN S. GARCIA 1 *, DAVID TALMY 2 AND ADAM C. MARTINY 1,3 DEPARTMENT OF EARTH SYSTEM SCIENCE , UNIVERSITY OF CALIFORNIA , IRVINE , CA , USA , DEPARTMENT OF EARTH , ATMOSPHERE AND PLANETARY SCIENCES , MASSACHUSETTS INSTITUTE OF TECHNOLOGY , CAMBRIDGE , MA , USA AND DEPARTMENT OF ECOLOGY AND EVOLUTIONARY BIOLOGY , UNIVERSITY OF CALIFORNIA , IRVINE , CA , USA * CORRESPONDING AUTHOR : n8garcia@gmail.com Received August 26, 2015; accepted December 10, 2015 Corresponding editor: Pia Moisander The ratio of elements such as carbon:nitrogen:phosphorus (C:N:P) in phytoplankton is known to vary substantially within single isolates and across environmental gradients. In addition, C:N:P is known to vary throughout the day due to diel patterns in nutrient acquisition and storage. It has been hypothesized that small phytoplankton such as marine cyanobacteria have relatively invariable elemental ratios during a 24 h period, whereas larger phytoplankton have a greater capacity to store elements and thus a wider diel range of C:N:P. To test this hypothesis, we examined diel vari- ability in cellular C:N:P, using a chemostat culturing system, for one of the most abundant marine cyanobacteria, Synechococcus (WH8102) during two 24 h periods. The cellular C quota nearly doubled during the 14 h light period and was subsequently reduced during the dark period. The cellular N quota also varied considerably, whereas the P quota remained relatively stable. These daily changes in elemental quotas led to highly variable C:N cell and C:P cell . Furthermore, the magnitude of variability in cellular elemental stoichiometry of Synechococcus was positively related to the growth rate. We constructed a model to test the extent to which variation in C:N cell and C:P cell is related to reserve carbon accumulation and depletion over each light –dark cycle. Results imply that, in addition to growth-related respiratory losses, Synechococcus also purges excess C during the dark period in order to maintain a nutritive balance within cells. Our data suggest that diel variation in C:N cell and C:P cell of Synechococcus is of the same order of magnitude as stoichiometric variation within plankton communities between major ocean environments. KEYWORDS: cyanobacteria; Synechococcus; stoichiometry; diel; Redfield; phytoplankton available online at www.plankt.oxfordjournals.org # The Author 2016. Published by Oxford University Press. All rights reserved. For permissions, please email: journals.permissions@oup.com