Biomass of Tomato Seedlings Exposed to an Allelopathic Phenolic Acid and Enriched Atmospheric Carbon Dioxide

Abstract

Increased atmospheric CO₂ can affect plant growth, so competition among plants may be influenced. Allelopathy is one mechanism involved in plant competition. Experiments were conducted in a controlled-environment chamber to determine if the concentration of atmospheric CO₂ altered 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 twice daily with nutrient solution amended with p-coumaric acid (4-hydroxycinnamic acid, HOC₆H₄CH = CHCO₂H; ranging 0–0.85 mg mL^-1; 5 concentrations in each experiment) and exposed 24 hr day^-1 in continuous-stirred tank reactors (CSTRs) to ambient air (335–375 ppm CO₂) or ambient air to which 350 ppm CO₂ was added (i.e., approximately twice-ambient CO₂; two CSTRs per CO₂ concentration in each experiment). Dose-response data relating p-coumaric acid concentration and shoot, root, and total biomass were fit to a flexible decay function. In all three experiments, twice-ambient CO₂ significantly increased the y-intercept for the dose-response model for the p-coumaric acid effect on shoot biomass by 25–50% but had negligible effects on other aspects of the models. Results suggest that if CO₂ affects plant competition, mechanisms involving allelopathic phenolic acids may not be involved.