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.
Highlights
Atmospheric carbon dioxide (CO2) is expected to rise from current levels of,390 parts per million to 700–1000 ppm by the end of this century, beyond the levels of the past 800 kyr of glacial-interglacial periods [1]
Carbonate chemistry system Carbonate chemistry parameters in our turbidostat cultures were representative of current ambient (,390 ppmv) and the end of this century (,750 ppmv), except that the estimated pCO2 level for cultures under the lowest growth light and elevated pCO2 treatment was significantly lower than in the cultures under higher growth lights (Table 1)
Cell volume, chlorophyll a (Chl a) and cellular protein Cell growth rate increased with culture growth light from low
Summary
Atmospheric carbon dioxide (CO2) is expected to rise from current levels of ,390 parts per million (ppm) to 700–1000 ppm by the end of this century, beyond the levels of the past 800 kyr of glacial-interglacial periods [1]. The elevated CO2 down-regulates the carbon concentrating mechanisms (CCMs) of phytoplankton, in particular in diatoms [5,6] Savings from this down-regulation are likely to allow compensatory increases in other processes such as phytoplankton growth [7,8,9], productivity [10] or synthesis of N-containing enzymes or cofactors [11]. Elevated CO2 had insignificant effects on the photophysiology of the marine diatom Chaetoceros brevis from the Antarctic Ocean [19], or on natural phytoplankton communities from the Derwent River estuary [20] or the Equatorial Pacific Ocean [21]. Such divergent responses to elevated CO2 complicate the implications of rising CO2 for marine phytoplankton
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