Effects of photochemical smog on growth, injury, and gas exchange of pine seedlings

Abstract

One-year-old seedlings of Pinus coulteri, P. pondersosa, P. jeffreyi, and P. sylvestris were exposed for 5 months to ambient photochemical smog (average 24-h monthly concentrations of ozone 0.067 to 0.108 ppm) in the San Gabriel Mountains of the Los Angeles Basin. Plants were grown in open-top chambers ("ambient-air" and "clean-air" treatments) and in outside plots. Rinsing of needles as well as scanning electron microscope observations revealed the highest deposition of particles to plants in the outside plots. No significant changes in growth in any of the studied species were observed. Exposure to photochemical smog had no significant effect on net photosynthesis and dark respiration in P. coulteri and P. ponderosa. Visual observation of injury showed that, by the end of the exposures, the P. ponderosa foliage in the ambient-air treatments was more damaged than in the clean-air treatment, but no negative effects on P. coulteri and P. jeffreyi foliage were seen. A tendency towards greater injury of P. sylvestris foliage in the ambient-air chambers and in the outside plots was also determined. Scanning electron microscope observations showed some subtle changes in the surface of P. coulteri and P. sylvestris in the ambient air treatment. Longer, multiseasonal exposures seem to be needed to study the effects of ambient concentrations of photochemical pollutants on forest trees.