Transcriptomic comparison in the leaves of two aspen genotypes having similar carbon assimilation rates but different partitioning patterns under elevated [cO \u3c inf\u3e 2 [

This study compared the leaf transcription profiles, physiological characteristics and primary metabolites of two Populus tremuloides genotypes (clones 216 and 271) known to differ in their responses to long-term elevated [CO2[ (e[CO2[) at the Aspen free-air CO2 enrichment site near Rhinelander, WI, USA. • The physiological responses of these clones were similar in terms of photosynthesis, stomatal conductance and leaf area index under e[CO2[, yet very different in terms of growth enhancement (0-10% in clone 216; 40-50% in clone 271). Although few genes responded to long-term exposure to e[CO2[, the transcriptional activity of leaf e[CO2[-responsive genes was distinctly different between the clones, differentially impacting multiple pathways during both early and late growing seasons. • An analysis of transcript abundance and carbon/nitrogen biochemistry suggested that the CO2-responsive clone (271) partitions carbon into pathways associated with active defense/response to stress, carbohydrate/starch biosynthesis and subsequent growth. The CO 2-unresponsive clone (216) partitions carbon into pathways associated with passive defense (e.g. lignin, phenylpropanoid) and cell wall thickening. • This study indicates that there is significant variation in expression patterns between different tree genotypes in response to long-term exposure to e[CO2[. Consequently, future efforts to improve productivity or other advantageous traits for carbon sequestration should include an examination of genetic variability in CO2 responsiveness. © 2009 New Phytologist