For investigations of ongoing processes in plants, such as photosynthesis in conifer leaves, nondestructive and noninvasive measuring techniques are needed. In this paper, a novel approach has been developed for the measurement of chloroplasts' numbers and pigment contents in conifer leaves based on the measurements of leaf absorption spectra using optical fibers and an array spectrophotometer. To eliminate the effect of scattering on the measured absorption spectra, a strategy has been applied taking advantage of the combined use of thin optical fibers normal to the needle's longitudinal axis and the phenomenon that scattering is largest in the forward direction. The optical path in the leaf is nearly the distance between the fiber tips; thus, we were able to obtain the absorption spectrum of the pigments in situ. A effect of the measured absorption spectra, occurring due to the organization of pigments in the leaf and interaction between light and leaf interior, can be accounted for by using the so-called Duysens transformation. Using this transformation, pigment contents and the relative number of chloroplasts can be obtained from the measured absorption spectra. We applied the method to observe pigment concentrations in different stages of the greening process in the leaves of two conifer species, Taxus baccata and Picea abies. The presented method may be used to estimate changes in chloroplast number and pigment content during various phases of greening of a species and to observe differences among various species.
Keywords: Duysens transformation; Leaf absorption spectra; Optical fibers; Pigment content; Relative chloroplasts’ number; Taxus baccata and Norwegian spruce.