Research Program Area: Ecosystem & Multimedia Effects
Topic Areas: Ecosystem Impacts
This report describes results of the 1989/1990 field studies on the effects of ambient and elevated ozone concentrations on growth, development of injury, physiological processes and chemistry of ponderosa pine (Pinus ponderosa Douglas ex Laws) seedlings. The study was performed at a typical ponderosa pine site at Shirley Meadow in the Greenhorn Range of the southern Sierra Nevada. In the study, the two-year old ponderosa pine seedlings from the Greenhorn Range stock were grown in pots filled with soil native to this location. To test the effects of air pollution, the seedlings were exposed in open-top chambers to four different treatments: 1) clean air; 2) clean air with the addition of ambient ozone concentrations; 3) clean air with the addition of doubled ambient ozone concentrations; and 4) ambient air. In addition, to test the effects of chamber enclosures on plant performance the plants were exposed to ambient air in the outside chamberless plots.
During the study, ambient ozone concentrations at Shirley Meadow were both elevated and typical of other southern Sierra Nevada locations. Ozone was the most important phytotoxic air pollutant in the area; however, concentrations of nitric acid vapor and ammonia were also elevated. In the first year of the exposures, no significant changes in growth of the seedlings exposed to the ambient ozone concentrations were determined. However, these seedlings had an increase of foliar injury and a tendency toward reduced net photosynthesis. For the seedlings exposed to the doubled ambient ozone concentrations, a significant increase of foliar injury was accompanied by increased senescence of the previous year's needles, reduced rates of net photosynthesis, and a tendency toward reduced chlorophyll fluorescence.
Effects of ozone on ponderosa pine seedlings became more pronounced during the second season of exposures. At ambient concentrations, the effects of ozone were still subtle; however, a significant increase of the previous year's foliar injury was accompanied by their premature senescence, a tendency toward reduced net photosynthesis and chlorophyll fluorescence and reduced starch accumulation in the foliage. At the doubled ambient ozone concentrations, increased needle in Jury was accompanied by decreased stomata1 conductance, net photosynthesis, chlorophyll fluorescence, pigment concentrations, and starch accumulation. As a result of these changes, biomass of foliage, stems, and roots of the plants was significantly reduced.
It was also shown that plants grown in the open-top chambers developed needles faster, had modified stomata1 conductance, and higher concentrations of foliar starch compared to the plants from the outside, chamberless plots.
For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753
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