Abstract
Relative spectral distributions of light during growth and for measurement do not only directly affect the net photosynthetic rate (Pn), but also affect the rate indirectly through their interaction. This letter explains a plausible mechanism of the interaction, some situations in which the interaction should be considered, and recommendations for selecting appropriate spectral distributions of measuring light to evaluate photosynthesis. A leaf adjusts the excitation energy distribution balance between photosystems in response to the relative spectral distribution of growth light. This adjustment modifies the response of Pn to the relative spectral distribution of measuring light. Therefore, evaluating the Pn of leaves of plants grown under different relative spectral distributions of growth light with a single spectral distribution of measuring light causes Pn overestimation or underestimation. The obtained results must be discussed in relation to the spectral distribution of measuring light to avoid producing biased evaluations. Depending on the study purpose, Pn should be evaluated under appropriate measuring light. For instance, in retrospective studies aimed at elucidating the causes of differences in growth brought about by the growth conditions, Pn should be measured under light with the same spectral distributions as those under which the plants were grown.
