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Reexamination of a canonical model for plant organ biomass partitioning¹

Department of Plant Biology, Cornell University, Ithaca, New York 14853-5908 USA

A previously proposed "canonical" model for the scaling relations among leaf, stem, and root biomass (M_L, M_S, and M_R, respectively) asserts that the proportional relations M_L M_S^3/4 M_R^3/4 and M_S M_R hold across seed plant species. This model is scrutinized by determining whether the scaling relations between M_L, M_S, and M_R vs. basal stem diameter D_S and between M_L, M_S, and M_R vs. plant height h are logically consistent with previously predicted scaling exponents. For example, if M_L is observed to scale as the 2-power of D_S and the model asserts that M_L M_S^3/4, then M_S must scale as the 8/3-power of D_S if the model is valid. Using a large data base for species with self-supporting stems, statistical support was found for most such comparisons between predicted and observed scaling relationships. However, this judgement is predicated on (1) the assertion that the scaling exponents for M_R with respect to D_S (or h) are numerically "deflated" due to a systematic underestimate of fine and small root biomass and (2) the stringent protocol used to calculate the 95% confidence intervals of scaling exponents, which favors rejection of the model. In light of these features, the "canonical" model is logically consistent with the new scaling relations reported here. Therefore, the model is judged valid within the context of this evaluation.

Key Words: allometry • biomass allocation • organ biomass • plant height • scaling relations • stem diameter

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