Black coloration in leaves of Ophiopogon planiscapus 'Nigrescens'. Leaf optics, chromaticity, and internal light gradients.

Abstract

Black-pigmented leaves occur only rarely in nature, possibly because their efficiency of light capture for photosynthesis is low. Using near-isogenic morphs of black- and green-leafed Ophiopogon planiscapus Nakai 'Nigrescens', we tested the possibility that black pigmentation restricts the transmission of PAR within the leaf. We measured chromaticity coordinates of black and green leaf phenotypes, quantified their pigments and optical properties, and followed the transmission profiles of red, blue and green light through lamina tissues. Chroma and lightness values for the black leaves were comparable to those of a black paint standard, and were lower than those for the green phenotype, or for green and anthocyanic leaves of three other species. The adaxial surface of black leaves absorbed 95% incident quanta, and reflected 4% across the entire 400-700 nm waveband. There were no obvious structural differences between black and green leaves. Black coloration correlated with luxuriant concentrations of both chlorophylls and anthocyanins in superficial mesophyll. Profiles of transmission of red and blue light were similar in green and black leaves. In contrast, green light was restricted to uppermost palisade mesophyll layers in black leaves, but was transmitted to more central mesophyll in green leaves.