Consistency between an allometric approach and optimal partitioning theory in global patterns of plant biomass allocation

1. Optimal partitioning theory (OPT) suggests that plants should allocate biomass to the organ that acquires the most limiting resource. An implied assumption of this is that there are trade-offs in allocation between leaf, stem and root functions. 2. Recently, an alternative approach, allometric biomass partitioning theory (APT), was developed to predict how plants should divide their metabolic production between leaves, stems and roots, based on the constraints of body size. APT predicts that, for an allometrically ideal plant, leaf mass should scale to the 3/4th power of body size, and stem and root mass should scale isometrically to body size. 3. In this study, we combine OPT with APT by investigating biomass partitioning not accounted for by allometric constraints across broad environmental gradients. 4. Intraspecific variability in biomass allocation shows correlations with environmental factors that would be predicted by OPT. However, interspecifically, these patterns either do not appear or are greatly reduced. 5. Our study suggests that, after size is accounted for, intraspecific residual variation in biomass allocation may be partially explained by environmental factors in a manner consistent with OPT. However, the particular patterns vary between species, obscuring large-scale patterns. 6. In summary, differences due to environmental variability can be incorporated with allocation patterns related to total mass to help understand how plants should allocate biomass in response to changes in both size and environment.