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

Abstract

Predictions 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 (lDMSP) and inorganic carbon fixation (lPOC) 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 lDMSP and lPOC were determined by measuring the incorporation of inorganic 13 C into DMSP and particulate organic carbon. Based on measurements over discrete time intervals during the day, a unique lDMSP vs. irradiance (P vs. E) relationship was established. Comparison is made with the P vs. E relationship for lPOC, indicating that light saturation of lDMSP occurs at similar irradiance to lPOC 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 lDMSP and lPOC 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.

The role of differential DMSP production and community composition in predicting variability of global surface DMSP concentrations

“…While an intriguing hypothesis, further studies are needed to understand if different DMSP synthesis genes explain the differential regulation of DMSP by LoDPs and HiDPs and to determine the DMSP synthesis genes of other organisms not predicted to contain dysB, DYSB, or TpMMT (e.g., Trichodesmium ). Future studies incorporating direct measurements of DMSP synthesis (Stefels et al ; Archer et al ) with genomic measurements (Curson et al , ) will help decipher the physiological mechanisms behind differential LoDP and HiDP regulation.…”

“…While an intriguing hypothesis, further studies are needed to understand if different DMSP synthesis genes explain the differential regulation of DMSP by LoDPs and HiDPs and to determine the DMSP synthesis genes of other organisms not predicted to contain dysB, DYSB, or TpMMT (e.g., Trichodesmium). Future studies incorporating direct measurements of DMSP synthesis (Stefels et al 2009;Archer et al 2017) with genomic measurements (Curson et al 2017(Curson et al , 2018 will help decipher the physiological mechanisms behind differential LoDP and HiDP regulation. While constraining the physiological mechanisms of DMSP for different phytoplankton types is critical for understanding the ecological roles of DMSP, simply differentiating between the two different types of DMSP producers was sufficient for reproducing the majority of observed spatial and temporal dynamics of in situ DMSP concentrations.…”

The interactive effects of stratospheric ozone depletion, UV radiation, and climate change on aquatic ecosystems

“…More recently, field experiments have shown that inhibition by UV radiation is also important for algal assemblages at lower latitudes and in the open ocean. 8,79 Exposure to UV radiation also inhibits synthesis of a key organosulfur compound, dimethylsulfoniopropionate, a marine precursor to dimethyl sulfide, a gas that helps ameliorate climate warming through the generation of sulphate aerosols. 8 Laboratory studies continue to investigate how environmental factors affect the response of phytoplankton to UV radiation, and the results of these are discussed in sections 3.2-3.4.…”

Response of dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) cell quotas to oxidative stress in three phytoplankton species

“…6). In the same context, a recent study using stable isotope incorporation into DMSP produced by natural phytoplanktonic communities showed that DMSP production on a diel timescale was coupled to carbon fixation rather than being stimulated at high light intensity, thus indicating that the regulation of DMSP production is not linked to photooxidative stress (Archer et al, 2018). Also considering the definition of an antioxidant as "any substance that, when present at low concentrations compared with those of an oxidizable substrate, significantly delays or prevents oxidation of that substrate" (Halliwell 1995), our observations rather support the hypothesis that DMSP and DMSO are simply damaged by ROS and do not exhibit any antioxidant property.…”

“…DMSO, DMS, acrylate, MSA and MSNA) (Stefels et al, 2007). Recent studies are now working with incorporation of stable isotope (D 2 O or NaH 13 CO 3 ) into DMSP to measure de novo DMSP synthesis rates (Stefels et al, 2009;Archer et al, 2018), which would be useful in studies aiming at deciphering the physiological roles of DMSP and its derivates.…”