Catechin, proanthocyanidin and lignin contents of loblolly pine (Pinus taeda) needles after chronic exposure to ozone

Concentrations of soluble and bound phenolic compounds were measured in needles of 3-yr-old loblolly pine (Pinus taeda L.) trees exposed from May to November 1993 to a range of ozone (O-3) concentrations in open-top field chambers. The treatments were charcoal-filtered air (CF), non-filtered air (NF), and NF air with O, added at 1.5 times (NF 1.5) and 2.0 times (NF 2.0) the ambient O-3 concentration for 12 h daily. Average daily (0800-2000 hours) O-3 concentrations in the CF, NF, NF 1.5 and NF 2.0 treatments were c. 29, 47, 76 and 98 nl l(-1), respectively, for the 140 d treatment period. At the end of the treatment period, total phenolic and proanthocyanidin concentrations in the previous year's needles were 25-29% higher in the NF 2.0 treatment compared with the lower O-3 treatments. Catechin concentration increased in the previous pear's needles by as much as 81% between the NF 2.0 treatment and the lower O-3 treatments. Catechin is an effective antioxidant, and elevated levels might confer some protection against O-3 injury. No significant differences in total phenolics and proanthocyanidins in the previous pear's needles were detected among the remaining O-3 treatments, or among any O, treatment for the current year's needles. Lignin content in needles of both years was not significantly affected by O-3 exposure. Changes in the phenolic content of older needles in response to elevated O, could alter plant-pathogen interactions and slow down microbial decomposition, which could contribute to a decline in site soil quality.