Hansman, Roberta L. and Sessions, Alex L. (2016) Measuring the in situ carbon isotopic composition of distinct marine plankton populations sorted by flow cytometry. Limnology and Oceanography: Methods, 14 (2). pp. 87-99. ISSN 1541-5856. http://resolver.caltech.edu/CaltechAUTHORS:20160301-075335319
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The carbon isotope ratio (δ^(13)C value) of marine particulates is a potentially useful tracer for elucidating pathways of carbon flow in the marine environment. Different species of phytoplankton vary in fractionation vs. CO_2 by up to 24‰ in laboratory cultures under varying nutrient and growth conditions, a signal that should propagate through the microbial food web. However, such contrasts have been difficult to confirm in field measurements due to analytical limitations. Here, we combine fluorescence-activated cell sorting (FACS) with a specialized micro-combustion interface and isotope-ratio mass spectrometry (SWiM-IRMS) to provide some of the first direct measurements of whole-cell δ^(13)C values for specific phytoplankton populations in the wild. For three samples collected off Scripps Pier in 2010–2011, Synechococcus averages δ^(13)C values of −25.7 ± 2.0‰, Prochlorococcus averages −23.0 ± 1.3, and diatoms average −20.8 ± 1.7‰. Diatoms were ∼3‰ enriched in ^(13)C when measured during a bloom (March 2011) as compared with mid-summer (July 2010). Sorted particles thought to represent living heterotrophic bacteria averaged −25.4 ± 2.5‰, whereas total filterable particles averaged −19.6 ± 1.0‰, indicating a strong similarity to diatom biomass. These variations demonstrate that in situ differences in δ^(13)C among different populations of particles can be exploited to follow carbon flow through successive trophic levels, and throughout organic matter remineralization, sinking, and preservation.
|Additional Information:||© 2016 Association for the Sciences of Limnology and Oceanography. Submitted 12 June 2015; Revised 23 September 2015; Accepted 24 September 2015. We would like to thank Mark Hildebrand at SIO for use of the Influx sorter, and Francesca Malfatti for providing the sorted diatom microscope pictures. Funding was provided by the Beckman Institute at Caltech and an Agouron Institute Fellowship to R.L.H.|
|Official Citation:||Hansman, R. L. and Sessions, A. L. (2016), Measuring the in situ carbon isotopic composition of distinct marine plankton populations sorted by flow cytometry. Limnol. Oceanogr. Methods, 14: 87–99. doi:10.1002/lom3.10073|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||01 Mar 2016 23:31|
|Last Modified:||01 Mar 2016 23:31|
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