| The purpose of this study was to determine how pretreatment stresses influenced subsequent allelopathic responses and to evaluate allelochemical uptake as a measurement of dose (i.e., effective concentration) which determines allelopathic responses.; Soil solution concentrations of allelopathic agents (e.g., phenolic acids) estimated by soil extractions differ with extraction procedure and the activities of soil sinks (microbes, clays, organic matter). This led to the hypothesis that root uptake of phenolic acids is a better estimator of dose than soil solution concentrations based on soil extracts. To test this hypothesis, cucumber seedlings were treated with ferulic acid in nutrient culture systems. Experiments used eleven ferulic acid concentrations ranging from 0 to 1 mM, phosphorus concentrations of 0.25, 0.5, and 1 mM, and pH of 4.5, 5.5, and 6.5 when cucumber seedlings were 9, 12, and 15 days old. The original hypothesis was rejected since the inhibition of net phosphorus uptake was related more frequently and more consistently to the initial ferulic acid solution concentrations surrounding seedling roots than to ferulic acid uptake by these roots. The data suggest that root contact, not uptake, is essential for the inhibitory activity of phenolic acids.; Experiments were also conducted to determine the potential for acclimation to allelopathic phenolic acids resulting from pretreatment of cucumber seedlings to allelochemical, drought, or nutrient stress. Seedlings were subsequently treated with 0, 0.25, 0.5, or 0.75 mM ferulic acid. Acclimation (tolerance) was quantified by % inhibition of net phosphorus uptake by ferulic acid. Pretreatment stresses reduced or eliminated the inhibitory activity of ferulic acid on net phosphorus uptake. The results suggest that a general acclimation response to a variety of pretreatment stresses can confer an increased tolerance of plants to allelopathic phenolic acids. |
