Remote sensing of crop responses to ozone and carbon dioxide treatments

Increases in tropospheric ozone (O₃) and carbon dioxide (CO₂) concentrations have been shown to alter crop responses such as gas exchange rates, leaf areas and specific leaf mass, plant biomass and yields. Leaf level alterations induced by exposure to pollutants are known to alter canopy reflectance characteristics. The objectives of this research are to evaluate the utility of non-imaging, ground-based, remote sensing measurements for detecting crop responses to alterations in atmospheric O₃ and CO₂ levels using crop plants grown in open-top chambers (OTCs). Winter wheat and soybeans were grown during the spring and summer months of 1995 in a 2×2 factorial arrangement of O₃ and CO₂ treatments. Canopy reflectance measurements were performed on several dates for both crops using a spectroradiometer (SE-590). Canopy reflectance, normalized reflectance, and the red edge response were determined and compared over gaseous treatments for use as a stress indicator for each crop. Spectral curves for both crops show minimal difference between treatments up to 700 nm but differ in soybeans for data beyond 700 nm. However, when reflectance data were normalized using the low O₃+ambient CO₂ as control, high O₃ and/or CO₂ treatments were separated for both crop species with different patterns for each. Likewise, red edge effects were different between O₃ treatments