Pigments and photoprotection in needles Pinus ponderosa with and without symptoms of ozone injury : 3rd EUROSILVA Workshop, Obergurgl, Austria, September, 10-14, 1998
The best documented ozone-induced damages on forest trees are found on Pinus ponderosa Dougl. ex P. & C. Laws. in the San Bernardino Mountains in Southern California. The foliar injury to this species is chracterized by specific visual symptoms ('chlorotic mottling'). In October 1997, ponderosa pine needles were collected at a severely impacted plot in the San Bernardino Mountains where individuals showing severe visual injury symptoms (symptomatic) and asymptomatic trees grow together. The symptomatic trees exhibit defoliation and thinned crowns caused by the premature loss of symptomatic needles (with typical 'chlorotic mottling') in late summer. At sampling time, the current year's flush and one-year old needles used for biochemical analysis did not show any or had only minimal symptoms of chlorotic mottle. In these needles, pigment concentrations in dark and light adapted needles were equal for the both symptomatic and asymptomatic trees, except for chlorophyll a decline in the previous year's needles of symptomatic trees in the light. However, the de-epoxidation state of the xanthophyll cycle in sun adapted needles of the symptomatic trees (35% de-epoxidised groups) was significantly higher than in needles of asymptomatic trees (20%). In the dark adapted stage, about 10% of de-epoxides were retained in all samples. These results indicate an increased need for photoprotection of the symptomatic trees in the light and an early stage of (reversible) chlorophyll degradation in the light. Since these alterations are detectable before visual symptoms appear on the needles, they might be useful for early indication of risk associated with phytotoxic ozone stress to pines.
