Elevated Atmospheric CO2 Effects on Cogongrass Ecotypes.

Cogongrass is an invasive C₄ perennial grass which is listed as one of the top ten worst weeds in the world and is a major problem in the Southeast US. Five cogongrass ecotypes (Florida, Hybrid, Louisiana, Mobile, and North Alabama) collected across the Southeast and a red-leaved ornamental (‘Red Baron’) variety were container grown for six months in open top chambers under ambient and elevated (ambient plus 200 ppm) atmospheric CO₂. Elevated CO₂ increased average dry weight (10 %) which is typical for grasses. Elevated CO₂ increased height growth, carbon content, photosynthesis, and both nitrogen and water use efficiencies, but lowered tissue nitrogen concentration; again, these are typical plant responses to elevated CO₂. The hybrid ecotype tended to exhibit the greatest growth (followed by Louisiana, North Alabama, and Florida ecotypes) while ‘Red Baron’ and Mobile ecotypes were smallest. There were few interactions of CO₂ with ecotype; when these were significant, the hybrid, Louisiana, Florida, and/or North Alabama ecotypes showed a positive response to CO₂ while the Mobile and ‘Red Baron’ ecotypes did not. Cogongrass is a problematic invasive weed in the southeastern U.S. and some ecotypes will likely become more so as atmospheric CO₂ continues to rise.