1 3 J Plant Res DOI 10.1007/s10265-016-0809-0 REGULAR PAPER Leaf color is fine-tuned on the solar spectra to avoid strand direct solar radiation Atsushi Kume 1 · Tomoko Akitsu 2 · Kenlo Nishida Nasahara 2 Received: 15 December 2014 / Accepted: 22 December 2015 © The Botanical Society of Japan and Springer Japan 2016 scattering in leaf tissues made the leaves grey bodies for PAR and enabled high PAR use efficiency. Terrestrial green plants are fine-tuned to spectral dynamics of incident solar radiation and PAR absorption is increased in various struc- tural hierarchies. Keywords Absorption spectra · Chlorophyll · Photosystem · Solar radiation spectra · Spectral matching · Terrestrial environment Introduction Physiological adaptation to different light intensities and spectral qualities is an important factor determining the dis- tribution of photosynthetic pigments in various organisms. The theory, known as “chromatic adaptation”, was first sug- gested by Engelmann (1883), and this adaptation in aquatic ecosystems has been studied for many years (e.g. Fujita and Hattori 1960; Kirk 2011). At depths with low light inten- sity, organisms acclimate to the prevailing blue-green light by increasing the amount of accessory pigments, such as carotenoids or biliproteins (Kirk 2011), which can absorb quanta of these wavelengths. Various chlorophylls also exist in aquatic ecosystems (e.g. Chl’s a, b, c 1 , c 2 , c 3 and d). Most of the changes in pigment composition are largely as acclimations to low irradiance, rather than to the spectral composition of underwater light (e.g. Dring 1981; Dutton and Juday 1944; Ramus 1983). The situation is quite dif- ferent in the terrestrial environment. Although several light- harvesting pigments exist, most land plants use specific light-absorbing pigments (Chl a, Chl b and carotenoids) to construct pigment-protein-complexes (Björn et al. 2009). Radiation within the 400–700 nm waveband is defined as photosynthetically active radiation (PAR) (McCree Abstract The spectral distributions of light absorption rates by intact leaves are notably different from the inci- dent solar radiation spectra, for reasons that remain elu- sive. Incident global radiation comprises two main com- ponents; direct radiation from the direction of the sun, and diffuse radiation, which is sunlight scattered by molecules, aerosols and clouds. Both irradiance and photon flux den- sity spectra differ between direct and diffuse radiation in their magnitude and profile. However, most research has assumed that the spectra of photosynthetically active radia- tion (PAR) can be averaged, without considering the radia- tion classes. We used paired spectroradiometers to sample direct and diffuse solar radiation, and obtained relation- ships between the PAR spectra and the absorption spectra of photosynthetic pigments and organs. As monomers in solvent, the spectral absorbance of Chl a decreased with the increased spectral irradiance (W m -2 nm -1 ) of global PAR at noon (R 2 = 0.76), and was suitable to avoid strong spec- tral irradiance (λ max = 480 nm) rather than absorb photon flux density (μmol m -2 s -1 nm -1 ) efficiently. The spec- tral absorption of photosystems and the intact thallus and leaves decreased linearly with the increased spectral irradi- ance of direct PAR at noon (I dir-max ), where the wavelength was within the 450–650 nm range (R 2 = 0.81). The higher- order structure of photosystems systematically avoided the strong spectral irradiance of I dir-max . However, when whole leaves were considered, leaf anatomical structure and light * Atsushi Kume glacier_foreland@yahoo.co.jp 1 Faculty of Agriculture, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan 2 Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8572, Japan