Warming up to carbon dioxide

Warming up to carbon dioxide
September 1, 2000

A recent cascade of government reports portends biospheric doom and gloom once increased temperatures and higher carbon dioxide (CO2) levels establish themselves. Though federal scientists acknowledge increased CO2 could benefit the biosphere, they maintain higher temperatures will overtake these gains and lead to an overall decline in plant productivity.

Indeed, researchers have found that photosynthesis is among the plant functions most sensitive to high-temperature damage. Still, two new articles have appeared recently, adding to the mountain of reports finding that plants thrive when atmospheric CO2 and temperatures rise.

With a giveaway title, “Growth in Elevated CO2 Protects Photosynthesis Against High-Temperature Damage,” an article from Taub and colleagues depicts how they grew several plant species in three Nevada research locations at ambient CO2 (near 350 parts per million [ppm]) and at elevated levels ranging from 750 ppm to 1,000 ppm. They fired up the heat on selected plants for a month or so to determine the effect of high-temperature stress on the CO2–photosynthesis relationship.

Time and time again, they found elevated CO2 increased the tolerance of photosynthesis to high temperatures. This conclusion, they write,

is based on both the fact that CO2-enhanced thermotolerance has been seen in plants grown in elevated CO2 in three different facilities . . . and that similar results were found using a variety of experimental protocols for exposure of leaves and plants to high temperature.

Furthermore, “this CO2-induced increase in plant high-temperature tolerance may have a substantial impact on both the productivity and distribution of many plant species in the 21st century.” Nice job!

In another study, Carter and colleagues noted that increased temperatures and increased CO2 may stress plants, thereby altering leaf pigmentation, leaf structures, and ultimately, leaf optical properties.

To test this notion, they grew sugar maple saplings for four years in open-top chambers in Oak Ridge, Tennessee. Some chambers had ambient temperature and CO2; others increased temperatures by 3°C; still others increased CO2 by 300 ppm; yet others had both increased temperature and CO2. Overall, they did not find that the elevated CO2 and/or temperature significantly altered the leaf optical properties.

One very interesting finding cannot be overlooked: During an “unusually hot, dry period,” photosynthesis was compromised, but, “This apparent stress reaction was ameliorated when CO2 was elevated.”

If temperatures heat up, these studies confirm, plants will adapt, so long as atmospheric CO2 levels keep pace.


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


References

Carter, G.A., R. Bahadur, and R.J. Norby, 2000. Effects of elevated atmospheric CO2 and temperature on leaf optical properties in Acer saccharum. Environmental and Experimental Botany, 43, 267-273.

Taub, D.B., J.R. Seemann, and J.S. Coleman, 2000. Growth in elevated CO2 protects photosynthesis against high-temperature damage. Plant, Cell and Environment, 23, 649-656.