Wavelength Dependence of Quantum Yield for CO2 Fixation and Photochemical Efficiencies of Photosystems I and II

摘要

Plants are continuously exposed to changes in the light spectrum, both short term and long term, due to changes in weather, the sun angle, and sun shade conditions. Of course, the absorption of incident light by a leaf is strongly wavelength dependent because different leaf pigments have different absorptance spectra; blue and red light are the most strongly absorbed, and leaves appear green because a relatively large proportion of green wavelengths are reflected rather than absorbed. However, even on an absorbed light basis, the quantum yield for CO2 fixation is wavelength dependent, with red light (600 to 640 nm) being the most effective and blue light (420 to 500 nm) the least effective. Causes that have been identified for the wavelength dependence of quantum yield of CO2 fixation include differential absorption by photosynthetic carotenoids and nonphotosynthetic pigments and an imbalanced excitation of the two photosystems (Terashima et al., 2009). One consequence of the latter cause is that plants have the capacity to optimize quantum yield for photosynthesis under variable conditions by altering photosystem composition and stoichiometry.