What physiological acclimation supports increased growth at high CO₂ conditions
2008
Spijkerman, Elly
Chlamydomonas acidophila Negoro is a green algal species abundant in acidic waters (pH 2-3.5), in which inorganic carbon is present only as CO₂. Previous studies have shown that aeration with CO₂ increased its maximum growth rate, suggesting CO₂ limitation under natural conditions. To unravel the underlying physiological mechanisms at high CO₂ conditions that enables increased growth, several physiological characteristics from high- and low-CO₂-acclimated cells were studied: maximum quantum yield, photosynthetic O₂ evolution (Pmax), affinity constant for CO₂ by photosynthesis (K₀.₅,p), a CO₂-concentrating mechanism (CCM), cellular Rubisco content and the affinity constant of Rubisco for CO₂ (K₀.₅,r). The results show that at high CO₂ concentrations, C. acidophila had a higher K₀.₅,p, Pmax, maximum quantum yield, switched off its CCM and had a lower Rubisco content than at low CO₂ conditions. In contrast, the K₀.₅,r was comparable under high and low CO₂ conditions. It is calculated that the higher Pmax can already explain the increased growth rate in a high CO₂ environment. From an ecophysiological point of view, the increased maximum growth rate at high CO₂ will likely not be realised in the field because of other population regulating factors and should be seen as an acclimation to CO₂ and not as proof for a CO₂ limitation.
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