Root and shoot growth vs. Biomass measurement in seedling bioassays

Allelopathy has been proposed as one mechanism that allows an introduced species to become invasive. The conventional techniques to evaluate the allelopathic potential of plants are the measurement of seedling growth (root and/or shoot growth, and dry weight). As the second of a 3-part investigation into the allelopathic potential of fennel (Foeniculum vulgare Mill.) on Santa Cruz Island, California (an island within Channel Islands National Park), this study compared the findings from both measurement techniques. Twelve introduced species of Mediterranean origin (6 forbs and 6 grasses species) that grow with fennel on Santa Cruz Island were selected. Two research questions guided this study:1) How do results from root/shoot growth measurements compare with dry seedling biomass measurement? 2) Does either technique provide more accurate results regarding the allelopathic potential of fennel? Bioassays showed significant inhibition in root and shoot elongation as fennel leachate concentrations increased to the maximum (5.0%). The dry biomass technique was not sensitive to determine the significant allelopathic interactions with the same precision as the root and shoot growth techniques. Since the measurement technique used may influence the understanding of the allelopathic potential of fennel, this study has practical implications for researchers that recommend how to effectively manage this invasive species.