BIOMASS OF TOMATO SEEDLINGS EXPOSED TO AN ALLELOPATHIC PHENOLIC-ACID AND ENRICHED ATMOSPHERIC CARBON-DIOXIDE

Increased atmospheric CO2 can affect plant growth, so competition amon g plants may be influenced. Allelopathy is one mechanism involved in p lant competition. Experiments were conducted in a controlled-environme nt chamber to determine if the concentration of atmospheric CO2 altere d the dose-response relationship between an allelopathic phenolic acid and tomato seedling biomass. Seeds of Lycopersicon lycopersicum were planted in quartz sand in styrofoam cups and allowed to germinate and grow for 15-17 days. During the next 14 days, seedlings were watered t wice daily with nutrient solution amended with p-coumaric acid (4-hydr oxycinnamic acid, HOC6H4CH = CHCO2H; ranging 0-0.85 mg mL(-1); 5 conce ntrations in each experiment) and exposed 24 hr day(-1) in continuous- stirred tank reactors (CSTRs) to ambient air (335-375 ppm CO2) or ambi ent air to which 350 ppm CO2 was added (i.e., approximately twice-ambi ent CO2; two CSTRs per CO2 concentration in each experiment). Dose-res ponse data relating p-coumaric acid concentration and shoot, root, and total biomass were fit to a flexible decay function. In all three exp eriments, twice-ambient CO2 significantly increased the y-intercept fo r the dose-response model for the p-coumaric acid effect on shoot biom ass by 25-50% but had negligible effects on other aspects of the model s. Results suggest that if CO2 affects plant competition, mechanisms i nvolving allelopathic phenolic acids may not be involved.