Wheat keeps winning!

Wheat keeps winning!
February 1, 2000

Throughout the world, wheat greatly benefits from each new molecule of carbon dioxide entering the atmosphere. Significant articles continue to appear in the major scientific journals reinforcing our view that this and many other major foodstuffs welcome the continued increase in atmospheric CO2 levels.

In central Arizona, Garcia and colleagues grew wheat in field plots that received CO2 near 370 parts per million (ppm) and elevated CO2 maintained near 550 ppm; 370 ppm is the current level, up from 270 ppm at the beginning of the Industrial Revolution. The soil nutrition was considered good, the roots were not limited by any type of pots, and the plants were well irrigated. The results were predictable: The elevated CO2 increased midday photosynthesis—the process that grows plants—by 28 percent and increased water-use efficiency by more than 30 percent.

This can only be seen as good news for wheat grown in the deserts of central Arizona as well as other dryland areas of the world. More wheat for less water is a winning combination, and elevated CO2 gets all the credit.

Plants become more efficient when CO2 levels increase, as Theobald and colleagues discovered when they grew wheat in growth chambers with ambient atmospheric CO2 concentrations near 360 ppm and other chambers with concentrations set at 700 ppm; they also varied the nitrogen supply to the wheat. Like an army of white-coats before them, these scientists found that growth at elevated CO2 increased photosynthesis. Quite simply, the chemical efficiency of wheat increased under elevated CO2. What’s more, they also found that atmospheric CO2 enrichment enhanced nitrogen-use efficiency. These findings imply that CO2 fertilization will benefit plants in a variety of soil fertility levels. And again, wheat grown in elevated CO2 consistently shows an increase in water use efficiency.

Some of CO2’s detractors persist in claiming that some intervening real-world “agent” will ruin the effects that have been proven in these and other experiments. Such dark clouds over the horizon often include tales of coming insects, plant diseases, weeds, or who knows what else. But the latest inspection of the literature turns up a very interesting paper that should make all wheat lovers sleep that much easier.

Wheat, like many other plants, does not passively sit by and allow outside agents to destroy it. After all, these plants have survived through eons of Earth’s evolution. In the case of wheat, a carbon-based compound, called a flavonoid, is produced that not only deters feeding from herbivores (like deer and rabbits) but also is detrimental to the growth of insects who select wheat for their daily diet.

Recognizing the importance of this compound, Estiarte and colleagues grew wheat in an open field in central Arizona with some plots receiving ambient CO2 levels of 370 ppm and other plots with CO2 maintained at 550 ppm. And you guessed it—elevated CO2 had all the other benefits for wheat detailed elsewhere.

But this study revealed a highly statistically significant increase—some 14 percent—in flavonoid concentrations for wheat grown in elevated CO2. The wheat not only grew bigger and more efficiently under elevated CO2, but also the plants wisely invested more of their carbon reserve on defense, protecting them from other human-induced insults, such as stratospheric ozone depletion and a resultant increase in damaging ultraviolet radiation. Estiarte wrote, “Flavonoids absorb the UV-B radiation and reduce its penetration into the leaf tissues, protecting the photosynthetic apparatus.” In layperson’s terms, the flavonoids protect the plants from sun damage.

Three facts are inevitable: Atmospheric CO2 will increase in the coming century; human populations will increase worldwide; and more wheat will be there to feed them. The evidence from these experiments shows that increased atmospheric CO2 is a blessing that has unlimited possibilities in generating the extra food needed in the next millennium.

We feel the pain of a hungry world, and we firmly believe that policies aimed at reducing atmospheric CO2 produce more harm than good. If we believe the world’s demand for wheat is likely to rise in the coming century, we cannot in good faith support any policy that would deprive wheat of the enormous and varied biological benefits of elevated CO2.


Robert C. Balling Jr., Ph.D. is director of the Laboratory of Climatology at Arizona State University and coauthor of The Satanic Gases.


References

Estiarte, M., et al., 1999, Free-air CO2 enrichment of wheat: Leaf flavonoid concentration throughout the growth cycle. Physiologia Plantarum, 105, 423–433.

Garcia, R.L., et al., 1998, Photosynthesis and conductance of spring-wheat leaves: field response to continuous free-air atmospheric CO2 enrichment. Plant, Cell and Environment, 21, 659–669.

Theobald, J.C., et al., 1998, Estimating the excess investment in ribulose-1,5-bisphosphate carboxylase/oxygenase in leaves of spring wheat grown under elevated CO2. Plant Physiology, 118, 945–955.