Limitation of dimethylsulfoniopropionate synthesis at high irradiance in natural phytoplankton communities of the Tropical Atlantic

Stephen D Archer,Timothy J Smyth,Ruth L Airs,Tracy Lawson,Jacqueline Stefels,Richard J Geider,Andrew P Rees

doi:10.1002/lno.10625

Abstract

AbstractPredictions of the ocean‐atmosphere flux of dimethyl sulfide will be improved by understanding what controls seasonal and regional variations in dimethylsulfoniopropionate (DMSP) production. To investigate the influence of high levels of irradiance including ultraviolet radiation (UVR), on DMSP synthesis rates (μDMSP) and inorganic carbon fixation (μPOC) by natural phytoplankton communities, nine experiments were carried out at different locations in the low nutrient, high light environment of the northeastern Tropical Atlantic. Rates of μDMSP and μPOC were determined by measuring the incorporation of inorganic 13C into DMSP and particulate organic carbon. Based on measurements over discrete time intervals during the day, a unique μDMSP vs. irradiance (P vs. E) relationship was established. Comparison is made with the P vs. E relationship for μPOC, indicating that light saturation of μDMSP occurs at similar irradiance to μPOC and is closely coupled to carbon fixation on a diel basis. Photoinhibition during the middle of the day was exacerbated by exposure to UVR, causing an additional 55–60% inhibition of both μDMSP and μPOC at the highest light levels. In addition, decreased production of DMSP in response to UVR‐induced photoxidative stress, contrasted with the increased net synthesis of photoprotective xanthophyll pigments. Together these results indicate that DMSP production by phytoplankton in the tropical ocean is not regulated in the short term by the necessity to control increasing photooxidative stress as irradiance increases during the day. The study provides new insight into the regulation of resource allocation into this biogeochemically important, multi‐functional compatible solute.

Highlights

The oceans emit approximately 28.1 (17.6–34.4) million tons of sulfur in the form of dimethyl sulfide (DMS) each year (Lana et al 2011), representing the largest natural flux of sulfur to the atmosphere
Several lines of evidence from this study indicate that on a diel basis DMSP synthesis is not enhanced when tropical and subtropical phytoplankton communities are exposed to natural high light levels that cause reversible photoxidative stress
P vs. E relationships based on lDMSP and lPOC and irradiance measured over discrete time intervals during the course of the day, showed similar values of photosynthetically active radiation (PAR) saturation (Ek)

Summary

Introduction

The oceans emit approximately 28.1 (17.6–34.4) million tons of sulfur in the form of dimethyl sulfide (DMS) each year (Lana et al 2011), representing the largest natural flux of sulfur to the atmosphere. The debate has intensified over the original proposal that DMS emission from the oceans contributed to an oceanic biology—climate feedback loop (Charlson et al 1987; Cainey et al 2008; Woodhouse et al 2010; Quinn and Bates 2011). This considerable source of sulfur has a substantial impact on. Parameterization of DMSP cell quotas has included the influence of light and/or nutrient availability and temperature dependence (e.g., Vallina et al 2008; Vogt et al 2010; Polimene et al 2012), reflecting possible physiological roles of DMSP

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Discussion

Conclusion