INHIBITION OF SCHIZACHYRIUM-SCOPARIUM (POACEAE) BY THE ALLELOCHEMICAL HYDROCINNAMIC ACID

Bare zones around shrubs in the Florida scrub indicate the possibility of allelopathy by shrubs controlling the distribution of grasses invading from adjacent sandhills. The allelochemical, hydrocinnamic acid, has been identified as a breakdown product of ceratiolin, which is released from the shrub Ceratiola ericoides. Hem, hydrocinnamic acid (HCA) was shown to have a strongly inhibitory effect on shoot and root biomass of the grass Schizachyrium scoparium in greenhouse bioassays lasting 4.5 months. Linear increases in the concentration of HCA from 0 to 200 ppm, applied biweekly, resulted in exponential decreases in root and shoot biomass at harvest. Plants grown at 200 ppm HCA had root and shoot biomasses 13% and 17% of controls, respectively. Concurrent investigation of reduced nutrient levels indicated greater inhibition by HCA in a reduced nitrogen (N) treatment and in a reduced potassium (K) treatment relative to HCA inhibition in the full nutrient treatment. The negative slopes of the regressions of log of biomass on HCA concentration were steepest in the reduced N and reduced K treatments. Root and shoot biomasses in reduced N treatments were 20-43% and 24-34% less than the respective biomasses in the full nutrient treatment. Comparable reductions in the reduced K treatment were as much as 19% and 10% for root and shoot biomasses, respectively. The effects of HCA in a reduced phosphorus (P) treatment and in a reduced P and K treatment were not significantly different from the effects of HCA in the full nutrient treatment. Extraction of the soils at harvest indicated no buildup of HCA at the end of the experiment. The sensitivity of Schizachyrium scoparium to HCA in general and increased sensitivity under low N and low K solutions may be important in the Florida scrub community where levels of N and K are known to be low.