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 (O3 ) concentrations in open-top field chambers, The treatments were charcoal-filtered air (CF). non-filtered air (NF), and NF air with O2 added at 1.5 times (NF 1.5) and 2(1 times (NF 2.0) the ambient O., concentration for 12 h daily. Average daily (0800-2000 hours) O3 concentrations in the CF. NF. NF 1.5 and NF 20 treatments were. 29. 47, 76 and 98 nl 1(-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 O3 treatments. Catechin concentration increased in the previous year's needles by as much as 81 % between the NF 2.0 treatment and the lower O3 treatments. Catechin is an effective antioxidant, and elevated levels might confer some protection against O3 injury. No significant differences in total phenolics and proanthocyanidins in the previous year's needles were detected among the remaining treatments, or among any O3 treatment for the current year's needles. Lignin content in needles of both years was not significantly affected by O3 exposure. Chances in the phenolic content of older needles in response to elevated O3 could alter plant-pathogen interactions and slow down microbiol decomposition, which could contribute to a decline in site soil quality.