Evaluation of ferulic acid uptake as a measurement of allelochemical dose:Effective concentration

Soil solution concentrations of allelopathic agents (e.g., phenolic acids) estimated by soil extractions differ with extraction procedure and the acti vities of the various soil sinks (e.g., microbes, clays, organic matter). T his led to the hypothesis that root uptake of phenolic acids is a better es timator of dose than soil solution concentrations based on soil extracts. T his hypothesis was tested by determining the inhibition of net phosphorus u ptake of cucumber seedlings treated for 5 hr with ferulic acid in whole-roo t and split-root nutrient culture systems. Experiments were conducted with II ferulic acid concentrations ranging from 0 to 1 mM, phosphorus concentra tions of 0.25, 0.5, or 1 mM, and solution pH values of 4.5, 5.5, or 6.5 app lied when cucumber seedlings were 9, 12, or 15 days old. The uptake or init ial solution concentration of ferulic acid was regressed on ferulic acid in hibition of net phosphorus uptake. Attempts were made to design experiments that would break the collinearity between ferulic acid uptake and phosphor us uptake. The original hypothesis was rejected because the initial ferulic acid solution concentrations surrounding seedling roots were more frequent ly and consistently related to the inhibition of net phosphorus uptake than to ferulic acid uptake by these roots. The data suggest that root contact, not uptake, is responsible for the inhibitory activity of phenolic acids.