Photosynthetic pigment contents in twigs of 24 woody species assessed by in vivo reflectance spectroscopy indicate low chlorophyll levels but high carotenoid/chlorophyll ratios

We have examined whether spectral reflectance indices used to non-destructively assess photosynthetic pigment levels and their ratios in leaves, could also be used for the same purpose in peridermal twigs. Regression lines of selected indices versus actual pigment levels, obtained from leaves and twigs of five species, suggested that semi-quantitative assessments are safe, provided that twig periderms could be easily removed. Given that, we proceeded to our next objective of screening a large number of species (24), in order to characterize their photosynthetic pigment profiles. Index comparisons between twigs and corresponding leaves indicated that twigs are characterized by lower levels of total chlorophyll and, unexpectedly, higher carotenoid/chlorophyll ratios. Moreover, the exposed and shaded sides of twigs displayed similar values for both indices in 80% of the species, suggesting that shade may not be the only factor shaping pigment levels and ratios. We discuss our results arguing that the distinct microenvironment within a twig may pose additional needs to the photosynthetic machinery, necessitating elevated carotenoid/chlorophyll ratios.