Carbon content

• Page authors: PRIMO
• Responsible curator: Hagen Buck-Wiese

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Phytoplankton carbon content
Approach: elemental analysis (CHN), biovolume conversion, or 13C incorporation
Context: environmental, lab
Spatial scale: point sample; single cell
Temporal scale: snapshot
Units: µg C L-1; pg C cell-1
Community captured: group and bulk
Co-measurements: cell abundance

Method Overview

Phytoplankton carbon content is measured by several approaches: (1) CHN elemental analysis of GF/F-filtered seawater, which yields bulk particulate organic carbon (POC) including all size fractions retained on the filter; (2) flow cytometric sorting of target cell populations followed by CHN analysis, providing group- or species-specific carbon content; (3) cell biovolume measurements by microscopy or flow cytometry, combined with empirical biovolume-to-carbon conversion relationships; or (4) ¹³C or ¹⁴C incorporation tracking over time.

Carbon content estimates are used to normalize primary production rate measurements and to derive carbon-specific growth rates.

Scale of measurement

Bulk POC measurements provide a community-level point estimate. Single-cell measurements (sorted CHN or nanoSIMS) provide cellular resolution, enabling distinction between carbon-rich and carbon-poor cells.

Data generated

Bulk POC (µg C L^-1) or per-cell carbon content (pg C cell^-1). When size-fractionated, contributions from different plankton size classes can be resolved.

Units & currency

Units are µg C L^-1 (bulk) or pg C cell^-1. The currency is carbon.

Sample size

Sample volumes range from single-cell to liters, depending on the approach.

Limitations

Bulk POC includes detrital and non-living carbon; phytoplankton-specific estimates require cell sorting or biovolume conversion. Biovolume-to-carbon conversion factors vary significantly with taxa, physiological state (e.g., nutrient limitation causes C:volume changes), and life stage. CHN analyses require careful procedural blanks and filter pre-combustion to avoid contamination. Detection limits may be a problem in oligotrophic waters.

Example Applications & Protocols

Classic examples

• Strathmann (1967) Estimating the organic carbon content of phytoplankton from cell volume or plasma volume

Common calculations/conversions

• Biovolume-to-carbon (non-diatoms): C (pg) = 0.261 × V^0.860 (Menden-Deuer & Lessard 2000); for diatoms: C (pg) = 0.288 × V^0.811.
• Specific growth rate (d^-1) = NPP / C_phyto.