Global allocation rules for patterns of biomass partitioning in seed plants

A general allometric model has been derived to predict intraspeciÞc and in-terspeciÞc scaling relationships among seed plant leaf, stem, and root biomass. Analysis of a large compendium of standing organ biomass sampled across a broad sampling of taxa inhabiting diverse ecological habitats supports the relations predicted by the model and deÞnes the boundary conditions for above- and below-ground biomass partitioning. These canonical biomass re-lations are insensitive to phyletic afÞliation (conifers versus angiosperms) and variation in averaged local environmental conditions. The model thus identiÞes and deÞnes the limits that have guided the diversiÞcation of seed plant biomass allocation strategies. Despite its importance to ecology, global cli-mate research, and evolutionary and ecological theory, the general principles underlying how plant metabolic production is allocated to above- and below-ground biomass remain un-clear (1–6). Indeed, there are few large data sets with which to evaluate patterns of standing bio-mass within and across the broad spectrum of vascular plant species (2, 7). The resulting un-certainty severely limits the accuracy of models for many ecologically and evolutionarily impor-tant phenomena across taxonomically diverse communities (8–11). Thus, although quantita-tive assessments of biomass allocation patterns are central to biology, theoretical or empirical assessments of these patterns remain conten-tious (2, 8, 10, 11). Nonetheless, the scaling relations among standing leaf, stem, and root (below-ground) biomass (ML, MS, and MR, respectively) can be derived analytically by first noting that the amount of resource used per individual plant, Ṙ0, approximates metabolic demand and gross photosynthesis (B) (12–14). Because B is pre-dicted to scale proportionally to total ML (Ṙ0} B} ML), theory predicts that the surface areas over which resources are exchanged with the environment (e.g., leaf surface area, which cor-relates with ML) are proportional to the 3/4 power of the total plant biomass (MT) (12–14)