The effect of elevated CO2 and temperature on the secondary chemistry of Betula pendula seedlings

The effect of elevated atmospheric CO2 and temperature on resource allocation and secondary chemistry of white birch (Betula pendula Roth) under a nonlimiting nutrient and water supply was investigated. Birch seedlings were grown in closed-top chambers exposed to ambient CO2 and temperature, elevated atmospheric CO2 (700 ppm), elevated temperature (2 degreesC above ambient) and a combination of elevated CO2 and temperature for one growing season. Elevated CO2 significantly increased the total biomass of the seedlings. The combined effect of the elevated CO2 and temperature treatments further increased the total biomass, but not significantly. The content of nitrogen and water decreased, while some secondary compounds (such as condensed tannins and flavonol glycosides) increased in leaves subjected to CO, enrichment. Elevated temperature increased the concentration of total flavone aglycones and decreased that of total HPLC-phenolics in the leaves, due to the decrease in individual flavonol glycosides, cinnamoylquinic acids and (+)-catechin. There were no significant interactive effects between CO2 and temperature in the phenolic concentrations of the leaves and in the stems, while the number of resin droplets in the top part of the stems showed significant interaction. This clearly implies that carbon allocation into secondary metabolites in the leaves and stems differ under enhanced CO2 and,temperature, and the combined effect of CO2 and temperature on the herbivore resistance of birches, is lower than that of CO2 and temperature alone.