Action spectra for photosynthesis in higher plants

The action and quantum yield spectra of photosynthetic CO2 uptake and the absorptance spectrum were determined for leaves of 33 species of higher plant including 7 arbores over the wavelength range 344–758 nm, to interpret various curves of the spectral responses. Almost the same curves either in the action or quantum yeild spectra were obtained for all the plants tested except in the ultraviolet (UV) and blue regions where the response relative to the red maximum was significantly lower in the arboreous than in herbaceous plants. The lower action in the UV and blue was seen in leaves having higher absorptance in the green, and a very close correlation (r=−0.920) was found between the ratio of action at 435 nm to that at 560 nm and the absorptance at 560 nm (A560). These facts proved that the variation of action spectra in the range from the UV to the green depended largely on the differences in absorptance of leaves in the green, and a curve with a pronounced second peak in the blue could be obtained when the A560 was less than about 0.6.