CO2TTON: The Sequel

Robert C. Balling, Jr., Ph.D.

Greening Earth Society Science Advisor

Botanists at Mississippi State University grew cotton at various temperatures under present and doubled CO2 levels. As we reported in the first CO2TTON, their work showed that elevated CO2 increased the total weight of the plants by over 30% while the weight of the bolls increased by over 20%. The cotton plants grew taller, had more and longer branches, and bigger leaves when grown under a doubled CO2 concentration. Reddy et al. showed that cotton plants benefit enormously from any increase in atmospheric CO2 levels.

A recent article in Crop Science provides even more good news for the "cotton club." Scientists in North Carolina grew cotton in open-top chambers with varying levels of atmospheric ozone (O3) and varying atmospheric CO2 concentrations. Heagle et al. noted that many others had found plant stress for elevated ozone levels, and enhanced growth and yield for elevated atmospheric CO2. They were particularly concerned with the interactions between ozone and CO2 that impact growth and cotton yield. They furthermore decided to vary the amount of nitrogen fertilizer applied to the plants.

The cotton plants were grown over two seasons under various environmental conditions within the chambers. Sure enough, CO2 enrichment generally stimulated plant growth and yield whereas ozone exposure suppressed both. Specifically, doubled CO2 at medium concentrations of nitrogen with low ozone produced an increase in the number of bolls of 23.3%. Seed-cotton weight (yield) increased 11.4%. Shoot weight increased 19%.

However, at elevated ozone levels with doubled CO2 the results were even more amazing. Doubled CO₂ at high ozone and medium nitrogen concentrations generated an increase in the number of bolls by 76.2%. Seed-cotton weight (yield) soared 96.4% and shoot weight by 91%. The authors succinctly state "Stimulation induced by CO2 increased as O3 stress increased."

One interpretation of their research – the one favored by the scientists in North Carolina – is that atmospheric ozone monitoring is critical in evaluating how different levels of CO2 impact cotton growth and yield as well as the growth and yield of many other plants susceptible to damage from elevated ozone levels. Fair enough. There is another interpretation. Cotton and the rest of Nature’s wonderful plants will be better off at higher concentrations of atmospheric CO2 than without it.

Reddy, K.R., Robana, R.R., Hodges, H.F., Liu, X.J., McKinion, J.M. 1998. Interactions of CO2 enrichment and temperature on cotton growth and leaf characteristics. Environmental and Experimental Botany, 39, 117-129.

Heagle, A.S., Miller, J.E., Booker, F.L., Pursley, W.A. 1999. Ozone stress, carbon dioxide enrichment, and nitrogen fertility interactions in cotton. Crop Science, 39, 731-741.