Productivity differences among loblolly pine genotypes are independent of individual-tree biomass partitioning and growth efficiency

Genetic differences in individual-tree biomass partitioning, growth efficiency, and stem relative growth rate (RGR) could confer intraspecific productivity differences and might strongly influence forest ecosystem carbon storage. We examined the relationship between genotype productivity (stem volume), whole-tree biomass partitioning, growth efficiency (stem wood production per unit leaf area), and stem RGR among nine different loblolly pine (Pinus taeda L.) genotypes from three different genetic groups of contrasting inherent genetic homogeneity: three open-pollinated (half-sib) families, three mass-control pollinated (full-sib) families, and three clonal varieties. We hypothesized that genotype productivity would be positively associated with increased partitioning to stem wood relative to other plant parts, higher stem RGR, and enhanced growth efficiency. After 3 years under plantation conditions, genotypes showed significant differences in stem volume, percent stem wood, percent branch wood, and partitioning to fine roots, yet no differences in stem RGR or growth efficiency. Furthermore, genotypic differences in stem volume were independent of genotypic differences in biomass partitioning, and overall, we found no evidence to support the hypothesized relationships. Even so, the observed variation in biomass partitioning has implications for forest C sequestration as genotypes which partition more biomass to long-lived biomass pools such as stems, may sequester more C. Moreover, the lack of a genetic relationship between stem volume and belowground partitioning suggests that highly productive genotypes may be planted without compromising belowground C storage.