Document: DAV-3-35-33

Analysis of relative growth rate in ecological experiments.

GRISE, D.J.*

Southwest Texas State University, San Marcos, TX 78666 USA ¹

Abstract:
Although rarely the central focus of a project, differences in relative growth rates are often used as supporting evidence to indicate differences between or among treatments. Poorter and Lewis (1986) presented a method that may be more accurate and more informative in determining differences among relative growth rates than the more common ANOVA of the relative growth rates themselves. A review of papers since 1990 indicates that very few investigators use Poorter and Lewis's method despite its apparent advantages and adaptability to different types of experimental designs. A greenhouse experiment demonstrates the advantages of this method and illustrates the additional information that can be gained by its use. In this experiment, Chenopodium album plants were grown in pots filled with sand at high and low nutrient levels. Four plants from each nutrient level were harvested every third day for a total of seven harvests. Analysis of variance, as described by Poorter and Lewis (1986), indicate relative growth rates for plants at the two nutrient levels were different (P = 0.001). Also, these differences in relative growth rate were maintained over the entire course of the experiment (P = 0.001). However, analysis of variance of growth rates themselves indicates relative growth rates differed between some, but not all, of the harvests. Analysis of relative growth rates calculated from harvest to harvest could lead to inaccurate or misleading interpretations of differences between relative growth rates.

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This abstract is being presented at: 3:30 PM in session:
Poster Session #17: Vegetative Analysis.