Competition and Allometry in Kochia scoparia

Comparisons between crowded and uncrowded Kochia scoparia individualsdemonstrate pronounced effects of competition on plant allometryas well as on the distributions of different aspects of size.Non-destructive measurements of height and stem diameter and,for a subset of the populations, the number and length of leavesand branches, were taken at three times, and the plants wereharvested after the third measurement. The sequential measurementsafforded the opportunity to obtain information of the effectsof competition on allometric growth trajectories of individuals,as well as on static inter-individual allometric relationships. The distributions of most size measures appeared to be normalfor the uncrowded population. Crowded populations developeda negatively-skewed height distribution and a high-inequalitymass distribution, whereas the diameter distributions remainednormal. Plants grown without neighbours showed simple allometricrelationships between height, diameter and weight. For isolatedplants, the 'static' allometric relationship between plantsof different sizes and the allometric growth trajectory of individualswere similar. Crowded populations showed complex allometry;the static inter-individual relationships between height, diameterand weight were curvilinear (on log-log scale). There were largedifferences in the allometric growth slopes of uncrowded vs.crowded plants. Allometric relationships between stem diameterand plant mass, and between total length of leaves and totallength of branches, did not seem to be altered by competition. The data suggest that height was the most important aspect ofsize influencing future growth of individuals in the crowdedpopulation. Only plants above a certain height were able tocontinue to grow from the second to third measurement in thecrowded population. This supports the hypothesis that asymmetriccompetition for light is the cause of the allometric changesand of the increase in size variability due to competition.Copyright1994, 1999 Academic Press Allometric growth, allometry, competition, growth, Kochia