Reflectance assessment of summer ozone fumigated Mediterranean white pine seedlings

Abstract

Seedlings of Pinus halepensis L. grown for three summers in open top chambers (OTC) in Northeastern Spain were exposed to three ozone (O 3) treatments: charcoal filtered air (CA), non-filtered (NF) and non-filtered plus 40 nl 1 −1 O 3 (FU). Ambient air plots (AA) in open air were established to assess the chamber effect. A clear seasonal trend was found in the physiological response of these pine seedlings in summer periods, with lower needle chlorophyll concentrations, and higher absorbance ratios for wavelengths at 435 nm and 665 nm ( A435 A665 ) which is indicative of carotenoid/chlorophyll a ratio. Old needles from the FU treatment had lower chlorophyll content and higher absorbance ratios ( A435 A665 ) than those of other treatments. Spectral reflectance indices assessing green biomass (NDVI), chlorophyll concentration (‘red edge’), the carotenoid/chlorophyll ratio (SIPI), and photosynthetic efficiency (SIXI) clearly followed the same seasonal trend, but were not statistically distinguishable from those of different ozone levels. These results are attributable to the dominance by the young needles in the sensor's field of view, which showed no clear biological differences with ozone treatment. Only ambient air seedlings presented different values for the reflectance indices in consonance with their lower chlorophyll content and higher carotenoid/chlorophyll ratio.