Antioxidants and protective pigments of Pinus ponderosa needles at gradients of natural stresses and ozone in the San Bernardino Mountains in California

At the San Bernardino Mountains, California, a well documented gradient of ozone pollution overlays a natural stress gradient from mesic to dry and fr om lower elevation to higher elevation sites. In contrast to gradient studi es in European regions, the highest ambient ozone levels are observed at lo w elevation and more mesic locations. In the present study, antioxidative a nd photoprotective systems in Pinus ponderosa needles were investigated at three plots - DW (1725 m, high ozone impact, mesic site), SW (1200 m, clean air, xeric site) and CO (above 2000 m, clean air and xeric site). Needles from the CO site contained significantly more total GSH (500 vs 300 nmol g( -1) dw in c needles), less alpha-carotene (6-10 vs 14-19 mu g mg(-1) total chlorophyll) and chlorophyll (1.7-2 vs 2.5-2.6 mg g(-1) dw in c+l needles) than those at the DW site. Furthermore,their xanthophyll cycle pool was in a more de-epoxidized state at midday (up to 60% in c needles), and the caro tenoid/chlorophylls ratios were generally higher. These patterns correspond to those observed at higher elevation plots in the Alps. On the other hand , needles from the high ozone site (DW) had a higher proportion of GSSG, in dicating the onset of biochemical injury to needles. Needles from the SW si te had intermediate proportions of GSSG. The results show the potential of environmental stressors to induce antioxidative and photoprotective respons es in the absence of elevated ozone concentrations, but support the oxidati ve effects of ozone injury to ponderosa pine.