Response of total tannins and phenolics in loblolly pine foliage exposed to ozone and acid rain.

Tannin and total phenolic levels in the foliage of loblolly pine (Pinus taeda L.) were examined in order to evaluate the effect of atmospheric pollution on secondary plant metabolism. The trees were exposed to four ozone concentrations and three levels of simulated acid rain. Tannin concentration (quantity per gram) and content (quantity per fascicle) were increased in foliage exposed to high concentrations of ozone in both ozone-sensitive and ozone-tolerant families. No effect of acid rain on tannins was observed. Neither total phenolic concentration nor content was significantly affected by any treatment, indicating that the ozone-related increase in foliar tannins was due to changes in allocation within the phenolic group rather than to increases in total phenolics. The change in allocation of resources in the production of secondary metabolites may have implications in herbivore defense, as well as for the overall energy balance of the plant.