Effects of Temperature and CO2Concentration on the Growth of Cotton (Gossypium hirsutum), Spurred Anoda (Anoda cristata), and Velvetleaf (Abutilon theophrasti)

Cotton, spurred anoda, and velvetleaf were grown in controlled-environment chambers at day/night temperatures of 32/23 or 26/17 C and CO 2 concentrations of 350 or 700 ppm. After 5 weeks, CO 2 enrichment to 700 ppm increased dry matter accumulation by 38, 26, and 29% in cotton, spurred anoda, and velvetleaf, respectively, at 26/17 C and by 61, 41, and 29% at 32/23 C. Increases in leaf weight accounted for over 80% of the increase in total plant weight in cotton and spurred anoda in both temperature regimes. Leaf area was not increased by CO 2 enrichment. The observed increases in dry matter production with CO 2 enrichment were caused by increased net assimilation rate. In a second experiment, plants were grown at 350 ppm CO 2 and 29/23 C day/night for 17 days before exposure to 700 ppm CO 2 at 26/17 C for 1 week. Short-term exposure to high CO 2 significantly increased net assimilation rate, dry matter production, total dry weight, leaf dry weight, and specific leaf weight in comparison with plants maintained at 350 ppm CO 2 at 26/17 C. Increases in leaf weight in response to short-term CO 2 enrichment accounted for 100, 87, and 68% of the observed increase in total plant dry weight of cotton, spurred anoda, and velvetleaf, respectively. Comparisons among the species showed that CO 2 enrichment decreased the weed/crop ratio for total dry weight, possibly indicating a potential competitive advantage for cotton under elevated CO 2 , even at suboptimum temperatures.