Rising CO2 Interacts with Growth Light and Growth Rate to Alter Photosystem II Photoinactivation of the Coastal Diatom Thalassiosira pseudonana

Abstract

We studied the interactive effects of pCO2 and growth light on the coastal marine diatom Thalassiosira pseudonana CCMP 1335 growing under ambient and expected end-of-the-century pCO2 (750 ppmv), and a range of growth light from 30 to 380 µmol photons·m−2·s−1. Elevated pCO2 significantly stimulated the growth of T. pseudonana under sub-saturating growth light, but not under saturating to super-saturating growth light. Under ambient pCO2 susceptibility to photoinactivation of photosystem II (σi) increased with increasing growth rate, but cells growing under elevated pCO2 showed no dependence between growth rate and σi, so under high growth light cells under elevated pCO2 were less susceptible to photoinactivation of photosystem II, and thus incurred a lower running cost to maintain photosystem II function. Growth light altered the contents of RbcL (RUBISCO) and PsaC (PSI) protein subunits, and the ratios among the subunits, but there were only limited effects on these and other protein pools between cells grown under ambient and elevated pCO2.

Thermal Performance Curves of Functional Traits Aid Understanding of Thermally Induced Changes in Diatom-Mediated Biogeochemical Fluxes

“…Furthermore, maximum growth rates were comparable to previously reported values for this strain; ∼0.9 d −1 at 18 • C and 80 µmol photons m −2 sec −1 (Li and Campbell, 2013). In contrast to other studies, we found that the thermal optimum range (17.0 and 20.1 • C, centered on 18.6 • C) was slightly colder than previously reported values (Thompson et al, 1992;Boyd et al, 2015) and may be due to the lower growth irradiance used in our study (Sandnes et al, 2005).…”

“…In contrast to other studies, we found that the thermal optimum range (17.0 and 20.1 • C, centered on 18.6 • C) was slightly colder than previously reported values (Thompson et al, 1992;Boyd et al, 2015) and may be due to the lower growth irradiance used in our study (Sandnes et al, 2005). In terms of morphological traits, absolute cell volumes were within range of previously reported values (Li and Campbell, 2013) and consistent with Thompson et al (1992), with cells becoming larger with increasing temperature (Figure 3A). These changes in cell volume, although small (i.e., ∼10%), may have significant implications for vertical export of carbon, as has been demonstrated in other small, spherical phytoplankton taxa (coccolithophores; Pantorno et al, 2013).…”

Effects of solar UV radiation on photosynthetic performance of the diatom Skeletonema costatum grown under nitrate limited condition

“…The PAR intensity that initiated the NPQ of N-limited grown cells was one fourth of that of N-replete grown ones. Light history would affect the photophysiological performances of phytoplankton when being shifted from the indoor-to outdoor-conditions, such as the S. costatum strain maintained in the laboratory for decades showed differential responses to UV compared to the strain isolated from coastal water (Guan and Gao 2008), and the Thalassiosira pseudonana showed differential photoinactivations of photosystem II after acclimating to different light levels (Li and Campbell 2013). In natural environments, the light acclimation from very low to very high levels with or without UVR also happens, such as that after typhoon event (Li et al 2009) or after heavy cloud covers for days or during a diel cycle (Gao et al 2007a), which would cause the exaggerated photoinhibition of S. costatum by solar PAR or UVR (Figs 2 & 3) although this diatom species could rapidly acclimate to the field light conditions (Guan and Gao 2008).…”

Species-Specific Variations in the Nutritional Quality of Southern Ocean Phytoplankton in Response to Elevated pCO2

“…In agreement with recommendations in best practice guides [38], we used a continuous culture system with CO 2 -enriched gas aeration to achieve stable carbonate chemistry that mimics the natural changes occurring due to ocean acidification. For a better understanding of how individual species will respond under natural conditions, we conducted our experiments at macronutrient concentrations reported for the area from which our strains were isolated (near shore coastal waters off Davis Station, Antarctica) and set the light intensity to a similarly high level, as light intensity can greatly alter the CO 2 -induced response of phytoplankton [39][40][41]. Furthermore, we chose to expose all species to continuous light to minimize diurnal variations which can mask CO 2 -induced changes [42].…”