Guest post by Indur M. Goklany

This illustration from a recent article in Science magazine shows that CO 2 is plant food. It is based on both empirical data and model results (not “data”). I know that looking at empirical data might seem like a novel idea to some people, but for some perverse reason, I find it more compelling.

On the right: Empirical Data. Growth of 21-day-old rice and S. viridis seedlings at different ambient CO 2 concentrations ranging from 30 to 800 parts per million. NOTE: The very last set of pots on the extreme right is out of sequence. They are for 390 ppm, while the next to last pots are for 800 ppm.

On the left, Modeled Data:

Modeled changes in CO 2 assimilation rate in response to changes in leaf intercellular CO 2 partial pressure for C 3 and C 4 photosynthesis and for a hypothetical C 4 rice. Curves 1, 2, and 4 have Rubisco levels typically found in a C 4 leaf (10 μmol m−2 catalytic Rubisco sites). Curve 3 shows a typical response for C 3 leaves with three times the Rubisco level of C 4 leaves. Curve 1 shows the response of a C 4 leaf with C 4 Rubisco kinetic properties. Curve 2 models how a C 4 leaf with C 3 Rubisco kinetic properties would respond (a hypothetical C 4 rice with C 3 Rubisco kinetics). The comparison of these two curves shows the increase in CO 2 assimilation rate achieved with C 4 compared with C 3 Rubisco kinetic properties within a functional C 4 mechanism. Arrows to curves 1 and 3 show intercellular CO 2 partial pressures typical at current ambient CO 2 partial pressures for C 4 and C 3 photosynthesis. To generate the curves, model equations were taken from (11) and comparative Rubisco kinetic constants from (12). (B) [Reference numbers per source.]

Source: Susanne von Caemmerer, W. Paul Quick, and Robert T. Furbank (2012). The Development of C 4 Rice: Current Progress and Future Challenges. Science 336 (6089): 1671-1672.

Finally, note that the top photograph on the right is for rice. According to Wikipedia, not always a reliable source, but in this case probably trustworthy:

[Rice] is the most important staple food for a large part of the world’s human population, especially in Asia and the West Indies. It is the grain with the second-highest worldwide production, after maize (corn), according to data for 2010. Since a large portion of maize crops are grown for purposes other than human consumption, rice is the most important grain with regard to human nutrition and caloric intake, providing more than one fifth of the calories consumed worldwide by the human species.

In other words, not only is CO 2 plant food, CO 2 makes human food. Guess some folks skipped that biology class.

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