We investigated whether changes in respiratory C fluxes, soil CO2 efflux, or root exudate quantity or quality explained differences in growth rates between closely related clones of Pinus taeda (L.). A factorial design with two clones, fertilized and control treatments, and four sequential harvests was installed in a greenhouse for 121 days. The two clones did show significant differences in respiratory C fluxes, soil CO2 efflux, and root exudation quantity and quality. While the clones also differed in growth rates, the C fluxes assessed in this paper did not explain how seedlings were able to allocate more C to stem growth in the months following fertilizer application. Changes in root exudation were not consistent with reduced heterotrophic soil CO2 efflux, which does not appear to be a plant-mediated process. These results indicate that if single genotypes are deployed over large land areas in plantations, dramatic differences between clonal plant-soil interactions may require consideration in ecosystem C budgets. Further, the range of belowground fluxes observed implies that genotype-specific C allocation may make some clones better able to exploit a given resource environment than others.
