Long-term effects of elevated carbon dioxide concentration and provenance on four clones of Sitka spruce (Picea sitchensis). I. Plant growth, allocation and ontogeny

Four clones of Sitka spruce (Picea sitchensis (Bong.) Carr.) from two provenances, at 53.2 degrees N (Skidegate a and Skidegate b) and at 41.3 degrees N (North Bend a and North Bend b), were grown near Edinburgh (55.5 degrees N), U.K., for three growing seasons in ambient (~350 micromol per mol) and elevated (~700 micromol per mol) CO2 concentrations under conditions of non-limiting water and nutrient supply. Bud phenology was not affected by elevated CO2] in the second growing season, but in the third year, the duration of shoot extension growth in three of the four clones (North Bend clones and Skidegate a) was significantly shortened, because of the suppression of lammas growth. Saplings in elevated CO2] had significantly greater dry masses of all components than saplings in ambient CO2]. However, comparison of relative component dry masses between plants of similar size showed no effect of CO2] treatment on plant allometric relationships. This finding, and the observed suppression of lammas growth by high CO2] during the third growing season suggests that the main effect of increasing CO2] is to accelerate sapling development. Clonal provenance did not affect dry mass production in ambient CO2]. However, in elevated CO2] the more southerly clones significantly out-performed the more northerly clones when grown at a latitude close to the latitudinal provenance of the Skidegate clones. As atmospheric carbon dioxide concentration rises, such changes in the relative performance of genotypes may be exploited for economic gain through appropriate selection of provenances for forest plantings.