Figure 1.

Leaf absorbance spectra of red- (circles) and yellow- (squares) senescing leaves of red-osier dogwood (A). Light response of effective PSII photon efficiency (Φ_PSII; calculated from ΔF/F_m′) in red- (circles) and yellow- (squares) senescing leaves illuminated from the leaf undersurface (B) as compared with those illuminated on the leaf upper surface (C). Measurements were made on detached leaves in a humidified chamber at constant gas concentration (380 μL L⁻¹ carbon dioxide, 21% [v/v] oxygen balanced with nitrogen gas) and temperature (20°C ± 2°C). Results for A through C are means for three leaves and error bars denote the sd.