The effects of caffeic acid, chlorogenic acid, t-cinnamic acid, p-coumaric acid, ferulic acid, gallic acid, p-hydroxybenzaldehyde, 5-sulfosalicylic acid, vanillic acid, and vanillin on growth, photosynthesis, water relations, and chlorophyll content of 3-week-old soybeans [Glycine max (L.) Merr. ‘Tracy’] grown in aerated nutrient solution were determined. At concentrations of 10−3 M, caffeic, t-cinnamic, p-coumaric, ferulic, gallic, and vanillic acids significantly reduced dry matter production, leaf expansion, height, leaf production, net assimilation rate (rate of dry matter production per unit leaf area), and leaf area duration (total leaf area present during treatment interval). Chlorogenic acid, p-hydroxybenzaldehyde, 5-sulfosalicylic acid, and vanillin at 10−3 M did not inhibit growth. None of the 10 compounds at 10−4 M inhibited growth. At concentrations of 10−3 M, caffeic, t-cinnamic, p-coumaric, ferulic, gallic, and vanillic acids severely reduced net photosynthetic rate and stomatal conductance of single, fully expanded leaves. These same compounds also caused marked reductions in leaf chlorophyll content, with net losses of chlorophyll occurring over an 86-h period after treatment.
