A Test of the Tilman Model of Plant Strategies: Relative Growth Rate and Biomass Partitioning

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Abstract
Tilman''s allocation model attempted to explain broad-scale patterns in plant morphology and vegetational structure. A fundamental assumption of this model is that the maximum relative growth rate of a species is negatively correlated with the ratio of non-photosynthetic to photosynthetic tissues that it possesses. We tested this assumption, and therefore Tilman''s model, using data of maximum relative growth rates and the ratio of root-to-shoot partitioning in 68 species of wetland angiosperm seedlings. We found no evidence for such a correlation at 10 d after germination (r = 0.19), and the hypothesis was rejected after 30 d (r = 0.20). There was a significant correlation opposite that predicted by Tilman''s model (r = 0.53) between the maximum relative growth rate of a species and the allometric relationship between root growth and shoot growth. Species that allocated part of their biomass to stem tissues had higher relative growth rates than did species without stems. According to these data, Tilman''s model must be rejected. We offer an alternative explanation of these trends, based on the concept of balanced growth.