Optical properties of halophyte leaves are affected by the presence of salt on the leaf surface

Abstract

Halophytes have developed a variety of adaptations to cope with excessive salt and other environmental constraints. These have resulted in altered leaf traits that affect the leaf optical properties and energy balance. In halophytes, there is often salt on the leaf surface due to salt aerosols and salt excretion from glandular cells. After examining the effects of the natural salt deposition on the leaf surface on the leaf light reflectance and transmittance, we defined the relationship between different leaf traits and the leaf optical properties in four halophytes (Atriplex prostrata, Atriplex portulacoides, Crithmum maritimum, and Limonium angustifolium). They differed significantly in the amount of naturally deposited salt on their leaves (range, 0.50-7.55 mg cm⁻²) and in the majority of the measured leaf traits. Differences were most pronounced for epidermal layer thickness, dry mass per leaf volume, and amount of UV-absorbing compounds. For the leaf optical properties, the salt on the leaf surface significantly reduced transmittance of UV, violet, and blue wavelengths. Redundancy analysis indicated that leaf upper epidermis thickness and leaf surface salt explained 58% and 7%, respectively, of the variability of the measured reflectance spectra. Leaf surface salt was particularly important for short wavelengths, explaining 35% of the reflectance variability in the UV region, and 20% in the violet and blue regions. The majority of the transmittance spectra variability was explained by leaf pigment content. These data reveal that leaf surface salt can function as a UV screen, to filter out potentially damaging short-wave radiation.