Genotypic variation for condensed tannin production in trembling aspen (Populs tremuloides, Salicaceae) under elevated CO2 and in high- and low-fertility soil

The carbon/nutrient balance hypothesis suggests that leaf carbon to nitroge n ratios influence the synthesis of secondary compounds such as condensed t annins. We studied the effects of rising atmospheric carbon dioxide on carb on to nitrogen ratios and tannin production. Six genotypes of Populus tremu loides were grown under elevated and ambient CO2 partial pressure and high- and low-fertility soil in field open-top chambers in northern lower Michig an, USA. During the second year of exposure, leaves were harvested three ti mes (June, August, and September) and analyzed for condensed tannin concent ration. The carbon/nutrient balance hypothesis was supported overall, with significantly greater leaf tannin concentration at high CO2 and low soil fe rtility compared to ambient CO2 and high soil fertility. However, some geno types increased tannin concentration at elevated compared to ambient CO2, w hile others showed no CO2 response. performance of lepidopteran leaf miner (Phyllonorycter tremuloidiella) larvae feeding on these plants varied acros s genotypes, CO2, and fertility treatments. These results suggest that with rising atmospheric CO2, plant secondary compound production may vary withi n species. This could have consequences for plant-herbivore and plant-micro be interactions and for the evolutionary response of this species to global climate change.