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 prove nances, 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 (similar to 350 mu mol mol( -1)) and elevated (similar to 700 mu mol mol(-1)) 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 (N orth Bend clones and Skidegate a) was significantly shortened, because of t he suppression of lammas growth. Saplings in elevated [CO2] had significant ly greater dry masses of all components than saplings in ambient [CO2]. How ever, 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 increasin g [CO2] is to accelerate sapling development. Clonal provenance did not aff ect dry mass production in ambient [CO2]. However in elevated [CO2] the mor e southerly clones significantly out-performed the more northerly clones wh en 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 t hrough appropriate selection of provenances for forest plantings.