Size-dependence of volatile and semi-volatile organic carbon content in phytoplankton cells

Sergio Ruiz-Halpern,Susana AgustÃ­,Carlos M. Duarte,Pedro Echeveste

doi:10.3389/fmars.2014.00025

Abstract

The content of volatile and semivolatile organic compounds (VOC and SOC), measured as exchangeable dissolved organic carbon (EDOC), was quantified in 9 phytoplanktonic species that spanned 4 orders of magnitude in cell volume, by disrupting the cells and quantifying the gaseous organic carbon released. EDOC content varied 4 orders of magnitude, from 0.0015 to 14.12 pg C cell-1 in the species studied and increased linearly with increasing phytoplankton cell volume following the equation EDOC (pg C cell-1) = -2.35 x cellular volume (CV, µm3 cell-1) 0.90 (± 0.3), with a slope (0.90) not different from 1 indicating a constant increase in volatile carbon as the cell size of phytoplankton increased. The percentage of EDOC relative to total cellular carbon was small but varied 20 fold from 0.28 % to 5.17 %, and no obvious taxonomic pattern in the content of EDOC was appreciable for the species tested. The cell release rate of EDOC is small compared to the amount of carbon in the cell and difficult to capture. Nonetheless, the results point to a potential flux of volatile and semivolatile phytoplankton-derived organic carbon to the atmosphere that has been largely underestimated and deserves further attention in the future.

Highlights

Recent methodological developments have enabled the measurement of the gaseous fraction of organic carbon dissolved in seawater, referred to as exchangeable dissolved organic carbon (EDOC)
The carbon content from cell volume using the equations in Verity et al (1992) were within the same order of magnitude as values previously reported for the same phytoplankton species (Table 1)
We provide here the first estimate of the EDOC content of phytoplankton cells, and assess the fraction of cell carbon represented by EDOC

Summary

Introduction

Recent methodological developments have enabled the measurement of the gaseous fraction of organic carbon dissolved in seawater, referred to as exchangeable dissolved organic carbon (EDOC). EDOC contains a numerous and largely unknown mixture of volatile (VOC) and semivolatile (SOC) organic carbon compounds (Park et al, 2013). This bulk measurement has drawn the attention to the role of this important, but largely overlooked, pool of carbon in marine ecosystems (Dachs et al, 2005; RuizHalpern et al, 2010). Knowledge of VOC and SOC content of marine autotrophs is limited to specific compounds released by marine primary producers (e.g., organohalogens, isoprenes, alcohols, and DMS) (Giese et al, 1999; Sinha et al, 2007). The total pool of EDOC contained in marine primary producers has not been reported as such yet

Methods

Results

Conclusion