CO2 modulation of the rates of photosynthesis and light-dependent O2 consumption in Trichodesmium

We established the relationship between gross photosynthetic O2 evolution and light-dependent O2 consumption in Trichodesmium erythraeum IMS101 acclimated to three targeted pCO2 concentrations (180 µmol mol-1 = low-CO2, 380 µmol mol-1 = mid-CO2 and 720 µmol mol-1 = high-CO2). We found that biomass (carbon) specific, light-saturated maximum net O2 evolution rates (PnC,max) and acclimated growth rates increased from low- to mid-CO2, but did not differ significantly between mid- and high-CO2. Dark respiration rates were five-times higher than required to maintain cellular metabolism, suggesting that respiration provides a substantial proportion of the ATP and reductant for N2 fixation. Oxygen uptake increased linearly with gross O2 evolution across light intensities ranging from darkness to 1100 µmol photons m-2 s-1. The slope of this relationship decreased with increasing CO2, which we attribute to the increased energetic cost of operating the carbon concentrating mechanism (CCM) at lower CO2 concentrations. Our results indicate that net photosynthesis and growth of T. erythraeum IMS101 would have been severely CO2 limited at the last glacial maximum, but that the direct effect of future increases of CO2 may only cause marginal increases in growth.

Boatman T. G., Davey P. A., Lawson T. & Geider R. J., 2018. CO2 modulation of the rates of photosynthesis and light-dependent O2 consumption in Trichodesmium. Journal of Experimental Botany: ery368. doi: 10.1093/jxb/ery368. Article (subscription required).

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