The effects of seed size on seedling growth response to elevated carbon dioxide in four conifer species

Four species of conifer were studied at both the interspecific and intraspecific levels to examine how variation in seed size affects early seedling growth response to elevated CO₂.; Elevated CO₂ affected the large-seeded Picea abies more positively than the small seeded Picea rubens. Differences in growth responses of the Picea were likely due to differences in relative growth rate (RGR) within the first two weeks of growth. Elevated CO₂ did not affect the growth of the Pinus species.; Intraspecific variation in seed size did affect growth, but there was no evidence of intraspecific differences in seed size on growth response to elevated CO₂ in any of the four species studied.; Contrasting growth responses to elevated CO₂ of seeds of different size, at the interspecific and intraspecific levels, are explained in terms of seed reserves and the ratio of energy to mineral nutrient reserves within the seed. Specifically, if energy reserves are increased to a greater extent than mineral nutrients as seed size increases, the CO₂ response will decrease.