Leaf optical properties in Liriodendrontulipifera and Pinusstrobus as influenced by increased atmospheric ozone and carbon dioxide

Seedlings of Liriodendrontulipifera L. and PinusstrobusL. were grown in open-top chambers in the field to determine leaf optical responses to increased ozone (O3) or O3 and carbon dioxide (CO2). In both species, seedlings were exposed to charcoal-filtered air, air with 1.3 times ambient O3 concentrations (1.3×), or air with 1.3 times ambient O3 and 700 μL•L−1 CO2 (1.3× + CO2). Exposure to 1.3× increased reflectance in the 633–697 nm range in L. tulipifera. Also, 1.3× decreased transmittance within the 400–420 nm range, increased transmittance at 686–691 nm, and decreased absorptance at 655–695 nm. With 700 μL•L−1 CO2, O3 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 1.3×, reflectance in P. strobus was not affected. However, 1.3× + 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 O3 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 = 0.82).