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Canonical rules for plant organ biomass partitioning and annual allocation¹

²Department of Plant Biology, Cornell University, Ithaca, New York 14853-5908 USA; ³Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona 85721 USA

Here we review a general allometric model for the allometric relationships among standing leaf, stem, and root biomass (M_L, M_S, and M_R, respectively) and the exponents for the relationships among annual leaf, stem, and root biomass production or "growth rates" (G_L, G_S, and G_R, respectively). This model predicts that M_L M_S^3/4 M_R^3/4 such that M_S M_R and that G_L G_S G_R. A large synoptic data set for standing plant organ biomass and organ biomass production spanning ten orders of magnitude in total plant body mass supports these predictions. Although the numerical values for the allometric "constants" governing these scaling relationships differ between angiosperms and conifers, across all species, standing leaf, stem, and root biomass, respectively, comprise 8%, 67%, and 25% of total plant biomass, whereas annual leaf, stem, and root biomass growth represent 30%, 57%, and 13% of total plant growth. Importantly, our analyses of large data sets confirm the existence of scaling exponents predicted by theory. These scaling "rules" emerge from simple biophysical mechanisms that hold across a remarkably broad spectrum of ecologically and phyletically divergent herbaceous and tree-sized monocot, dicot, and conifer species. As such, they are likely to extend into evolutionary history when tracheophytes with the stereotypical "leaf," "stem," and "root" body plan first appeared.

Key Words: allometry • biomass allocation • organ biomass • plant growth

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