Abstract
A Fraunhofer Line Radiometer (FLR) measured solar-excited chlorophyll a fluorescence (
F) as an indicator of photosynthetic capacity in leaves of
Washingtonia robusta (palm) and
Vitis vinifera (grape). Under clear skies, the FLR utilized the Fraunhofer line-depth principle (FLDP) to detect
F within the O
2 absorption band centered at 687 nm wavelength. On 20 April, the morning after soils were treated with the photosystem II herbicide DCMU
F increased significantly (
p = 0.05) in palm, while leaf reflectance at 687 nm (
R) did not change. By 21 April, leaf herbicide concentrations were lethal. Increased
F and
R in palm corresponded with net photosynthetic rates near zero. Photosynthesis in grape also decreased greatly, but
F and
R remained similar to the controls. Results for palm indicate that
F could be measured while leaves remained exposed to full sunlight, and support earlier work to indicate a potential role for the FLDP in remotely sensing
F and photosynthetic capacity.