Wu, Z., Zeng, B., Li, R. and Song, L. 2012. Combined effects of carbon and phosphorus levels on the invasive cyanobacterium, Cylindrospermopsis raciborskii. Phycologia 51: 144-150.
The authors write that "in marine phytoplankton, studies have shown that rising atmospheric CO2 can enhance their growth (Riebesell et al., 1993; Kranz et al., 2010), primary production (Hein and Sand-Jensen, 1997) and nitrogen fixation (Levitan et al., 2007)." But they add that "the impacts of elevated atmospheric CO2 on freshwater habitats are still poorly understood."
What was done
In an effort designed to rectify this latter situation, the four Chinese scientists isolated specimens of the freshwater N2-fixing cyanobacterium (Cylindrospermopsis raciborskii) from a pond near Dianchi Lake in Kunming (China); and they cultured them semi-continuously for 18 days at low and high inorganic phosphorus (Pi) levels (0.022 ÁM and 22 ÁM, respectively) in contact with air of either 380 or 1000 ppm CO2, while measuring several important physiological functions of the cyanobacterium.
What was learned
In the case of light-saturated net photosynthesis, the 620-ppm increase in the air's CO2 content resulted in 37% and 74% increases in the low and high Pi treatments, respectively. In the case of biomass growth, the CO2 increase resulted in 26% and 23% increases in the low and high Pi treatments, respectively. And in the case of nitrogen fixation, the CO2 increase resulted in 36% and 14% increases in the low and high Pi treatments, respectively.
What it means
Wu et al. say that the cyanobacterial growth increase they observed "confirms previous studies with other algae (Burkhardt and Riebesell, 1997; Burkhardt et al., 1999; Clark and Flynn, 2000; Kim et al., 2006; Posselt et al., 2009; Kranz et al., 2010)," as well the finding of Chinnasamy et al. (2009) that "the nitrogenase activity of Anabaena fertilissima increased with increasing levels of CO2." Thus, it would appear that in both marine and freshwater ecosystems, continued increases in the air's CO2 content should significantly enhance the wellbeing of various species of phytoplankton.
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