Reflectance spectra and images of green leaves with different tissue structure and chlorophyll content

Abstract

Reflectance images of various intact leaves were taken in four selected bands at 440, 550, 690, and 800 nm and compared with their reflectance spectra in the visible to near infra-red (range: 400 to 800 nm). The images showed high local resolution over the leaf surface (0.025 mm² per pixel) with a low spectral resolution, whereas the reflectance spectra were acquired with a high spectral resolution (1 nm). In addition, the individual leaf samples were further characterized by their specific colorimetric values for visual impression (CIE 1931). The results demonstrate that leaf reflectance is determined by the following basic parameters: (a) the leaf pigment content (absorption of chlorophylls and carotenoids in the pigment protein complexes of chloroplasts and, in red leaves, also of epidermal anthocyanins), (b) the leaf tissue structure (size of aerial interspaces between cells, which influence leaf optical properties), and (c) the structure of the leaf surface (e.g., waxes and hairs). These in-vivo measurements of leaves have the advantage of being fast and non-destructive, with the possibility for high-throughput evaluation and repetition measurements. The data are discussed in view of their importance for basic research (e.g., stress detection) and quality assessment of plant material ranging from contact measurements to remote sensing.

Keywords:

• anthocyanins
• carotenoids
• chlorophylls
• hairs
• leaf optics
• waxes