PRIMARY AND SECONDARY EFFECTS OF WATER CONTENT ON THE SPECTRAL REFLECTANCE OF LEAVES

TLDR

Primary effects arise from water’s radiative properties, while secondary effects cannot be explained solely by these properties. The study aimed to determine the primary and secondary effects of water content on leaf spectral reflectance across six species. The authors collected leaves from six species with diverse internal structures and measured their spectral reflectance in the laboratory. Decreased leaf water content increased reflectance across 400–2500 nm, with greatest sensitivity in water absorption bands near 1450, 1940, and 2500 nm and also between 400–720 nm due to pigment absorption; wavelength‑independent secondary effects were minor compared to primary and pigment‑related secondary effects.

Abstract

Leaves of six species selected to represent a broad range in internal structure were collected in the field and studied in the laboratory to determine primary and secondary effects of water content on leaf spectral reflectance. Primary effects were those that resulted solely from the radiative properties of water. Secondary effects were those that could not be explained solely by these properties. Decreased leaf water content generally increased reflectance throughout the 400‐2,500‐nm wavelength range. For the aquatics Eichhornia crassippes and Nuphar luteum, the broadleaved trees Liquidambar styraciflua and Magnolia grandiflora, the cane‐grass Arundinaria tecta, and the needle‐leaved Pinus taeda, the sensitivity of reflectance to water content was greatest in the water absorption bands near 1,450, 1,940, and 2,500 nm. Sensitivity maxima occurred also between 400 and 720 nm, indicating secondary effects that resulted from decreased absorption by pigments. Secondary effects of water content on reflectance that were largely wavelength‐independent, together with any wavelength‐independent effects of leaf internal structure, were far less significant than primary and secondary effects resulting from decreased absorption by water and pigments, respectively.