THE ALLOMETRY OF PLANT REPRODUCTIVE BIOMASS AND STEM DIAMETER

The allometry of reproductive biomass M was determined for one moss (Polytrichum commune), four pteridophytes (Psilophyton princeps, Psilotum nudum, Lycopodium lucidulum, and L. clavatum), six gymnosperms (Larix decidua, Pseudotsuga douglasii, Tsuga canadensis, Pinus rigida, Picea abies, and Taxus baccata), and two angiosperms (Crataegus sp. and Quercus bicolor). Biomass M was measured for individual and grouped reproductive organs and regressed as a function of stem diameter D measured proximal to M for representative reproductive stems from each species. Published data for Cooksonia pertoni were used to estimate sporangial M. The data from this vascular plant fossil were compared to those from other species. Least squares regression of the entire data set yielded M = 0.12D2.9 (r2 = 0.94, N = 215), indicating that M, on the average, compiled with M is-proportional-to D(alpha almost-equal-to 3.0). The allometries of the moss, pteridophyte, gymnosperm, and angiosperm species, however, were M = 0.46D4.6 (r2 = 0.99, N = 41), M = 0.07D3.2 (r2 = 0.91, N = 65), M = 0.56D2.2 (r2 = 0.92, N = 85), and M = 0.44D1.8 (r2 = 0.97, N = 21), respectively, indicating that the proportionality M is-proportional-to D(alpha almost-equal-to 3.0) recedes with finer taxonomic resolution. The data for Cooksonia were found to comply with the allometry of Polytrichum when the regression curve of this moss was extrapolated into the size range of the fossil species. Analyses showed that intraspecific allometric scaling factors alpha were dependent upon the manner in which plant stems taper. Species or portions of branching systems with alpha > 4.0 had essentially untapered stems (e.g., Polytrichum commune, Psilotum nudum, twigs of Larix decidua); species with alpha < 2.2 had tapered stems resulting from secondary growth in most cases. The evolution of tapered primary stems and secondary growth was interpreted to alter reproductive allometry.