Limestone dust alters the optical properties and traits of Fagus sylvatica leaves

KEY MESSAGE : Limestone dust altered spectral signatures of hypo-stomatal Fagus sylvatica leaves, mitigated the effect of high air temperatures, stimulated the production of chlorophylls, and reduced the amount of photo-protective compounds. Human activities and global changes to the environment result in increased concentrations of mineral dust in the atmosphere. This can have an impact on light harvesting in plants, and their energy balance and water management. The horizontally oriented, hypo-stomatal leaves of Fagus sylvatica present an efficient trap for dust particles. Two-year-old seedlings were treated for 3 weeks with two different concentrations of limestone dust from a quarry (median particle size 2 µm), and then, leaf optical properties and selected morphological, biochemical, and physiological traits were examined. Their adaxial and abaxial cuticle thickness and palisade/spongy parenchyma ratio were negatively correlated with dust concentration. For leaf biochemistry, chlorophyll levels were positively correlated with dust concentration, while the correlations of UV absorbing substances with dust concentration were negative. High-dust treatment positively affected the potential photochemical efficiency of photosystem II in the leaves, potentially due to lower leaf temperature. The reflectance spectra of the leaves following different dust treatments differed significantly along the visible and UV-A spectral regions, while they were most affected in the near infrared. The dust concentration explained 74 % (p = 0.001) of the variability of the reflectance spectra and only 20 % (p = 0.024) of the transmittance spectra. The present short-term study reveals that limestone dust can have positive effects on leaves with abaxial stomata, although the reduced photoprotection presents a risk of photoinhibition if the dust is removed by wind or water.