LEAF OPTICAL-PROPERTIES IN LIRIODENDRON-TULIPIFERA AND PINUS-STROBUS AS INFLUENCED BY INCREASED ATMOSPHERIC OZONE AND CARBON-DIOXIDE

Seedlings of Liriodendron tulipifera L. and Pinus strobus L. were grown in open-top chambers in the field to determine leaf optical responses to increased ozone (O-3) or O-3 and carbon dioxide (CO2). In both species, seedlings were exposed to charcoal-filtered air, air with 1.3 times ambient O-3 concentrations (1.3X), or air with 1.3 times ambient O-3 and 700 mu L . L(-1) CO2 (1.3X + CO2). Exposure to 1.3X increased reflectance in the 633-697 nm range in L. tulipifera. Also, 1.3X decreased transmittance within the 400-420 nm range, increased transmittance at 686-691 nm, and decreased absorptance at 655-695 nm. With 700 mu L . L(-1) CO2, O-3 did not affect reflectance in L. tulipifera, but decreased transmittance and increased absorptance within the 400-421 nm range and increased transmittance and decreased absorptance in the 694-697 nm range. Under 1.3X, reflectance in P. strobus was not affected. However, 1.3X + CO2 increased pine reflectance in the 538-647, 650, and 691-716 nm ranges. Transmittances and absorptances were not determined for P. strobus. Reflectance in both species, and transmittance and absorptance in L. tulipifera, were most sensitive to O-3 near 695 nm. Reflectance at 695 nm, but particularly the ratio of reflectance at 695 nm to reflectance at 760 nm, was related closely to ozone-induced decreases in leaf chlorophyll contents, particularly chlorophyll a (r(2) = 0.82).