INTERSPECIFIC DIFFERENCES IN WHOLE-PLANT RESPIRATION VS. BIOMASS SCALING RELATIONSHIPS: A CASE STUDY USING EVERGREEN CONIFER AND ANGIOSPERM TREE SEEDLINGS

Premise of the study: Empirical studies and theory indicate that respiration rates (R) of small plants scale nearly isometrically with both leaf biomass (M L) and total plant biomass (M T). These predictions are based on angiosperm species and apply only across a small range of body mass. Whether these relationships hold true for different plants, such as conifers, remains unclear. Methods: We tested these predictions using the whole-plant maintenance respiration rates and the biomass allocation patterns of the seedlings of two conifer tree species and two angiosperm tree species. Model Type II regression protocols were used to compare the scaling exponents (a) and normalization constants (alpha) across all four species and within each of the four species. Key results: The data show that the scaling exponents varied among the four species and that all differed significantly from isometry. For conifers, scaling exponents for R vs. M T, and R and M L were numerically smaller than those of the broadleaved angiosperm species. However, across the entire data set, R scaled isometrically with M L and with M T as predicted by the West, Brown, and Enquist (WBE) theory. We also observed higher respiration rates for small conifer seedlings compared to comparably sized angiosperm seedlings. Conclusions: Our data add credence to the view that the R vs. M scaling relationship differs among species, and that in general, the numerical values of this interspecific scaling relationship will depend on the species pooled in the analysis and on the range of body sizes within the data set.