Memo to Doubters—I was Tempted to say “Deniers”—CO2 is Plant Food!

Guest post by Indur M. Goklany

This illustration from a recent article in Science magazine shows that CO₂ 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 CO₂ 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 CO₂ assimilation rate in response to changes in leaf intercellular CO₂ partial pressure for C₃ and C₄ photosynthesis and for a hypothetical C₄ rice. Curves 1, 2, and 4 have Rubisco levels typically found in a C₄ leaf (10 μmol m⁻² catalytic Rubisco sites). Curve 3 shows a typical response for C₃ leaves with three times the Rubisco level of C₄ leaves. Curve 1 shows the response of a C₄ leaf with C₄ Rubisco kinetic properties. Curve 2 models how a C₄ leaf with C₃ Rubisco kinetic properties would respond (a hypothetical C₄ rice with C₃ Rubisco kinetics). The comparison of these two curves shows the increase in CO₂ assimilation rate achieved with C₄ compared with C₃ Rubisco kinetic properties within a functional C₄ mechanism. Arrows to curves 1 and 3 show intercellular CO₂ partial pressures typical at current ambient CO₂ partial pressures for C₄ and C₃ 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 C₄ 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 CO₂ plant food, CO₂ makes human food.  Guess some folks skipped that biology class.