Effects of Atmospheric CO2 Enrichment on Oceanic Carbon and Nitrogen Fixation
Garcia, N.S., Fu, F.-X., Breene, C.L., Bernhardt, P.W., Mulholland, M.R., Sohm, J.A. and Hutchins, D.A. 2011. Interactive effects of irradiance and CO2 on CO2 fixation and N2 fixation in the diazotroph Trichodesmium erythraeum (Cyanobacteria). Journal of Phycology 47: 1292-1303.
In a laboratory study designed to explore this latter possibility, Garcia et al. examined the effects of present-day (~380 ppm) and elevated (~750 ppm) atmospheric CO2 concentrations on CO2 and N2 fixation by T. erythraeum isolates from the Pacific and Atlantic Oceans under a range of irradiance conditions.
The seven scientists determined that "the positive effect of elevated CO2 on gross N2 fixation was large (~50% increase) under mid and/or low irradiances compared with that at high light (~20% increase)," noting that data from Kranz et al. (2010) and Levitan et al. (2010) corroborate their findings. In fact, they report that in the Kranz et al. study, "under low light, gross N2-fixation rates were 200% higher in a high-CO2 treatment (900 ppm) compared with a low-CO2 treatment (150 ppm), whereas under high light, gross N2-fixation rates were only 112% higher under elevated CO2." In the case of CO2 fixation, on the other hand, they found that CO2-fixation rates increased significantly "in response to high CO2 under mid- and high irradiances only."
As the atmosphere's CO2 concentration continues to rise, this phenomenon should boost the growth rates of marine diazotrophic cyanobacteria and enable them to make more nitrogen available to themselves and co-occurring species, which should ultimately act to significantly increase both the quantity and quality of the worldwide phytoplanktonic food base that ultimately supports all marine animal life.
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