Why do genotypes of Picea glauca differ in their growth response to elevated CO 2?

Abstract

Meta-analyses reveal that fast-growing species have a greater growth response to elevated CO 2 than slow-growing species. It is unknown whether this is a direct response or whether inter-specific differences in growth are simply correlated with other physiological or morphological differences among species that affect the growth response to CO 2. Here we use intra-specific variation in Picea glauca to examine the mechanistic basis for this relationship. Relative growth rate (RGR) of 29 genotypes grown at ambient (370 μll -1) or elevated (740 μll -1) CO 2 was measured. Physiological and morphological traits describing differences in allocation, canopy structure, stomatal function and photosynthesis were determined. Most variation in RGR (74%) was explained by traits associated with canopy structure. Although there was a strong correlation between RGR740 and RGR370, we found no evidence that genotypes that grew fast at ambient CO 2 had a greater relative growth response to CO 2. Given that the pattern found at the intra-specific level differed from that reported at the inter-specific level, our results suggest that RGR per se does not affect the growth response to CO 2. Rather, the CO 2 growth response is determined by traits that may or may not be correlated with RGR. © The Author 2011. Published by Oxford University Press. All rights reserved.