Organ partitioning and distribution across the seed plants: Assessing the relative importance of phylogeny and function

Understanding how plant biomass is distributed between roots, stems, and leaves is central to many questions in life-history evolution, ecology, and ecosystem studies. Current ecological dogma states that patterns of biomass partitioning result from environmental differences. However, there are methodological issues associated with the role of plant size. In addition, the importance of evolutionary history in biomass distribution is unclear. Here, we assess the relative importance of evolutionary history and growth form on how biomass not accounted for by plant size is partitioned between plant organs. Our analyses indicate that while growth form was significantly correlated with variation in biomass distribution and partitioning, phylogeny appears to be the strongest factor. Variation in biomass distribution is phylogenetically conserved for leaf mass but not for stems, roots, and annual production, suggesting that these factors may be more plastic. Leaf mass was the only organ with a considerable portion of the residual variation from growth form, which appears to be largely the result of differences in leaf traits. Our results have important implications for ecological studies because partitioning studies must first assess the role of plant size and evolutionary history in order to fully understand variability in biomass partitioning and distribution.