CO2 Effects on Nitrogen Fixation in Soybeans
Lam, S.K., Hao, X., Lin, E., Han, X., Norton, R., Mosier, AR.., Seneweera, S. and Chen, D. 2012. Effect of elevated carbon dioxide on growth and nitrogen fixation of two soybean cultivars in northern China. Biology and Fertility of Soils 48: 603-606.
To further explore this topic and working at a free-air carbon dioxide enrichment (FACE) facility in Changping, Beijing, China, Lam et al. grew two cultivars (Zhonghuang 13, a high-protein cultivar, and Zhonghuang 35, a high-oil cultivar) of soybean (Glycine max L.) from seed to maturity at either ambient or elevated atmospheric CO2 concentrations (415 or 550 ppm, respectively) under conditions of adequate fertility and water supply. And what did they learn?
The seven scientists report that the elevated CO2 treatment increased the above- and below-ground biomass of Zhonghuang 13 by 18.3 and 11.1%, respectively, while it increased the above- and below-ground biomass of Zhonghuang 35 by 15.6 and 20.0%, respectively. They additionally note that the high-CO2 treatment also boosted the percentage of N derived from the atmosphere (%Ndfa) for Zhonghuang 13 from 59% to 79%, corresponding to an amount of N fixed ranging from 166 to 275 kg N ha-1; but they say that the elevated CO2 treatment "had no significant effect on either parameter for Zhonghuang 35."
The Chinese researchers say their results suggest that "variation in N2 fixation ability in response to elevated CO2 should be used as a key trait for selecting cultivars for future climate with respect to meeting the higher N demand driven by a carbon-rich atmosphere." And it should be noted, in this regard, that it is most interesting that it was the high-protein (nitrogen-needing) cultivar that experienced the greatest increase in %Ndfa (34%) as a result of the nearly identical 33% increase in the atmosphere's CO2 concentration.
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