A Grass Act

A Grass Act
May 1, 2000

With winter snowstorms now a fading memory, it’s time to focus attention on the verdant lawn that is soon to become a source of pride in high-sun months. As you tune up your mower and check your supply of fertilizer and weed killers, why not take a moment to appreciate a major source of grassy health, one that is effective and virtually free of charge: carbon dioxide.

Indeed, the scientific literature is alive with evidence that increased atmospheric CO2 is a fantastic partner in any effort to cultivate the lawn of your dreams—as five recent studies attest.

A team of scientists from Kansas State University grew grass in open-top chambers with ambient (natural) and twice-ambient atmospheric CO2 levels. Like hundreds of experiments before, this one found that elevated CO2 significantly increased above-ground biomass. Furthermore, the researchers reported that the “time required for developing leaves to achieve maximum leaf area was reduced by 29 percent.” The grass expanded out faster and stayed green longer thanks to increased CO2.

Taking a cue from the Emerald Isle, Jongen and Jones grew grasses from the Irish lowlands in open-top chambers with atmospheric CO2 levels of a near-ambient 350 parts per million (ppm) and a doubled 700 ppm. You guessed it—CO2 enrichment caused a 26 percent increase in total biomass.

Any suburbanite worth his grass seed realizes that a healthy root system is the key to a terrific lawn. What would you say to a 28 percent increase in shoot biomass and a 42 percent increase in root biomass? Those were the findings when van Ginkel and Gorissen compared ryegrass grown at 350 ppm with that grown at 700 ppm CO2. Of course, an increase in below-ground biomass in turn spurs microbial activity that further enhances overall growth.

And that’s exactly what happened to ryegrass and clover grown for several years at ambient and elevated CO2 levels in Switzerland. In that experiment, Marilley and colleagues and found that CO2 tended to increase beneficial bacterial numbers in the soil in close proximity to plant roots.

If it seems like your grass strives skyward only moments after you’ve finished mowing, you may be right. Where CO2 is on the rise, grass springs eternal.


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


References

Jongen, M., and M.B. Jones, 1998. Effects of elevated carbon dioxide on plant biomass production and competition in a simulated neutral grassland community. Annals of Botany, 82, 111-123.

Knapp, A.K., et al., 1999. Elevated CO2 and leaf longevity in the C4 grassland-dominant Andropogon gerardii. International Journal of Plant Sciences, 160, 1057-1061.

Marilley, L., et al., 1999. Influence of an elevated atmospheric CO2 content on soil and rhizosphere bacterial communities beneath Lolium perenne and Trifolium repens under field conditions. Microbial Ecology, 38, 39-49.

Skinner, R.H., et al., 1999. Carbon and nitrogen reserve remobilization following defoliation: Nitrogen and elevated CO2 effects. Crop Science, 39, 1749-1756.

van Ginkel, J.H., and A. Gorissen, 1998. In situ decomposition of grass roots as affected by elevated atmospheric carbon dioxide. Soil Science Society of America Journal, 62, 951-958.