Towards a carbon budget of the diazotrophic cyanobacterium Crocosphaera: effect of irradiance

S Rabouille,G Semedo Cabral,Ml Pedrotti

doi:10.3354/meps12087

Abstract

Towards a carbon budget of the diazotrophic cyanobacterium Crocosphaera: effect of irradiance

Highlights

In the open ocean, organic matter originates from the fixation of atmospheric carbon by photoautotrophic organisms
Carbohydrate contents, whether expressed per biovolume or per carbon unit, did increase with irradiance up to 200 μmol photons m−2 s−1 (p < 0.01), pointing to a reserve accumulation in cells. This increase in carbohydrate storage saturated beyond 200 μmol photons m−2 s−1 (Fig. 3B). These results indicate that carbon accumulation is not to be related to the increase in cell size only; at higher light levels there is an increase in total carbon with larger proportions of particulate organic carbon (POC) found as carbohydrates: 50% at 200 μmol photons m−2 s−1 versus 29% at 50 μmol photons m−2 s−1
In line with observations in the eukaryote Emiliania huxleyi (Engel et al 2004), we found that carbon exudation as exopolymeric substances (EPS) in the prokaryote C. watsonii WH8501 is constitutive of growth and increases with the rate of carbon acquisition

Summary

Introduction

Organic matter originates from the fixation of atmospheric carbon by photoautotrophic organisms. While the elemental composition of bulk organic material is very consistent in the world’s oceans, with molar proportions of C:N:P = 106:16:1 (Redfield 1934, Redfield et al 1963), there is evidence for anomalous surface dissolved inorganic carbon (DIC) drawdown, exceeding the amounts predicted from nitrate availability and the Redfield C:N ratio (Sambrotto et al 1993). This apparent overconsumption of DIC in regard to nitrogen in phytoplankton cells suggests that organic. Diazotrophs would represent an important trophic link in sustaining the biological pump in oligotrophic oceans

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