RESPONSE OF LEAF SPECTRAL REFLECTANCE IN LOBLOLLY-PINE TO INCREASED ATMOSPHERIC OZONE AND PRECIPITATION ACIDITY

Leaf reflectance responses to increased ozone and precipitation acidity were determined at visible (400-720 nm) and infra-red (720-2500 nm) wavelengths for field-grown seedlings of loblolly pine (Pinus taeda L.). Treatments were maintained continuously from 3 April to 3 November. In a relatively ozone-sensitive variety of pine, increased ozone decreased visible and infra-red reflectance by late May. By late August, continued exposure to ozone increased visible and infra-red reflectance. As of late November, ozone at 1.7 x ambient or greater concentrations had increased visible reflectance substantially in an ozone-insensitive as well as the ozone-sensitive variety. Acidic precipitation decreased visible and infra-red reflectances in both varieties in May and decreased infra-red reflectances in the ozone-sensitive variety in August, but did not produce significant reflectance responses in November. Visible reflectance responses to ozone and acidic precipitation, particularly those near 700 nm, were spectrally similar to reflectance responses reported previously for other deleterious environmental influences.