Abstract
The aim of this in vitro study was to investigate the effects of six phenolic acids applied individually and in combination at concentrations of 0-20 mM on Ambrosia artemisiifolia and soil bacteria. Chlorogenic acid (CGA), p-hydroxybenzoic acid (PHBA), and protocatechuic acid (PKA) were tested on both plants and bacteria, whereas p-coumaric (PCA), vanillic (VA), and ferulic (FA) acids were tested only on soil bacteria. The estimated EC(50) for radicle inhibition were 4.9 ± 0.1 mM for PHBA, 4.1 ± 0.7 mM for CGA, 6.6 ± 0.7 mM for PKA, 10.1 ± 0.9 mM for CGA + PHBA + PKA, 4.6 ± 0.4 mM for ferulic, vanillic, and p-coumaric acids (FA + VA + PCA), and 2.5 ± 0.3 mM for the combination of all six phenolic acids. Bacterial strains were less susceptible to individual phenolic acids compared to their combinations. PKA and CGA showed the strongest antibacterial activity, with PKA inhibiting 78% and killing 74% of strains at ≤10 mM, while CGA inhibited 61% and killed 57%. Conversely, PCA and VA had the weakest antibacterial effects, requiring ≥20 mM for complete inhibition. Among test genera, Stenotrophomonas, Bacillus, Peribacillus, and Pseudomonas were more susceptible than Enterobacter and Lelliottia. Subinhibitory concentrations of individual phenolic acids did not affect bacterial motility, except for PKA. The study suggests that VA, PCA and FA alone or combined and PHBA alone, appear promising for weed management. Reduced herbicide strategies may safely incorporate CGA and PKA at concentrations below 2.5 mM.