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https://ir.library.oregonstate.edu/concern/articles/j67315433

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  • We investigated the effects of elevated pCO₂ on cultures of the unicellular N₂-fixing cyanobacterium Crocosphaera watsonii WH8501. Using CO₂-enriched air, cultures grown in batch mode under high light intensity were exposed to initial conditions approximating current atmospheric CO₂ concentrations (~400 ppm) as well as CO₂ levels corresponding to low- and high-end predictions for the year 2100 (~750 and 1000 ppm). Following acclimation to CO₂ levels, the concentrations of particulate carbon (PC), particulate nitrogen (PN), and cells were measured over the diurnal cycle for a six-day period spanning exponential and early stationary growth phases. High rates of photosynthesis and respiration resulted in biologically induced pCO₂ fluctuations in all treatments. Despite this observed pCO₂ variability, and consistent with previous experiments conducted under stable pCO₂ conditions, we observed that elevated mean pCO₂ enhanced rates of PC production, PN production, and growth. During exponential growth phase, rates of PC and PN production increased by ~1.2- and ~1.5-fold in the mid- and high-CO₂ treatments, respectively, when compared to the low-CO₂ treatment. Elevated pCO₂ also enhanced PC and PN production rates during early stationary growth phase. In all treatments, PC and PN cellular content displayed a strong diurnal rhythm, with particulate C:N molar ratios reaching a high of 22:1 in the light and a low of 5.5:1 in the dark. The pCO₂ enhancement of metabolic rates persisted despite pCO₂ variability, suggesting a consistent positive response of Crocosphaera to elevated and fluctuating pCO₂ conditions.
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