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TECHNICAL REPORTS

Plant and Environment Interactions

Tropical Spiderwort (Commelina benghalensis L.) Increases Growth under Elevated Atmospheric Carbon Dioxide

USDA-ARS, National Soil Dynamics Lab., 411 S. Donahue Dr., Auburn, AL 36832

^* Corresponding author (andrew.price{at}ars.usda.gov).

Received for publication November 27, 2007. Although considerable effort is being spent studying exotic plant pests, little consideration has been given as to how invasive plants might react to the increasing concentration of CO₂ in the atmosphere. Tropical spiderwort (Commelina benghalensis L.) is considered one the world's worst weeds and is becoming more of a problem in agricultural settings of the southeastern USA. Growth responses of tropical spiderwort were evaluated using plants grown in containers with a soilless potting medium under ambient and elevated (ambient + 200 µmol mol^–1) levels of CO₂ in open-top field chambers. Although plant height was unaffected by CO₂, leaf and flower number tended to increase (approximately 23%) when exposed to elevated CO₂. Aboveground plant parts exhibited significant increases in dry weight when exposed to high CO₂; leaf, flower, stem, and total shoot dry weights were increased by 36, 30, 48, and 44%, respectively. Total plant dry weight was increased by 41% for plants grown under high CO₂. Root dry weight and root length were unaffected by CO₂ concentration. Tropical spiderwort allocated more biomass to stems and tended to allocate less to roots when plants were exposed to high CO₂. Plant carbon concentration and content tended to be higher in CO₂–enriched plants, whereas plant nitrogen concentration tended to be lower; thus, elevated CO₂–grown plants had higher C/N ratios. Also, the amount of biomass produced per unit nitrogen was higher for plants exposed to elevated CO₂. The growth response of this plant is in the upper range typical for C3 plants.