Allocation tradeoffs among chaparral shrub seedlings with different life history types (Rhamnaceae)

Abstract

California chaparral shrub species have different life history types: Nonsprouters (NS) are killed by fire and persist through a fire-stimulated seed bank; facultative sprouters (FS) reestablish by a combination of vegetative sprouting and seeding; and obligate sprouters (OS) reestablish exclusively by sprouting. Nonsprouters and FS establish seedlings in open-canopy postfire environments, whereas OS establish seedlings between fires in the shady understory. We hypothesized that allocation differences among seedlings of postfire sprouters and nonsprouters and regeneration niche differences would lead to contrasting patterns in biomass accumulation (NS > FS > OS, in sun; OS > FS > NS, in shade). Seedlings of three species from each life history type were grown in sun and 75% shade. We measured net carbon assimilation and biomass accumulation after one year. Biomass accumulation was similar in the sun except FS>OS. In the shade, NS had lower biomass than FS and OS. Assimilation rates, nitrogen relations, and allocation differences could not fully explain biomass accumulation differences. Instead, biomass accumulation was inversely related to water-stress tolerance and shade tolerance. Additionally, OS and FS differed in root/shoot allocation even though both are sprouters. Seedling growth and carbon assimilation rates were divergent among three life history types and were consistent with differences in tolerance to water stress and shade or sun regeneration niches, but not tradeoffs in sprouting-related allocation differences per se.