New paper: 'Reflections of stress: Ozone damage in broadleaf saplings can be identified from hyperspectral leaf reflectance'

Anna Lee Jones, Adam Ormondroyd, Felicity Hayes, Elizabeth S. Jeffers, Environmental Pollution, 360 (2024) 124642

https://doi.org/10.1016/j.envpol.2024.124642

At the ground level ozone is a highly oxidising air pollutant produced by a sunlight catalysed reaction of nitrous oxides and volatile organic compounds. Ground level ozone concentrations are increasing despite efforts to curb vehicular emissions, and baseline ozone concentrations are predicted to continue to rise until the end of the century. Ozone pollution is highly toxic to plants, causing reduced productivity, early leaf drop and vulnerability to other stressors. Deciduous trees are more susceptible to ozone damage than coniferous trees due to increased stomatal conductance. Ozone causes characteristic injury symptoms on the leaf surface, but our monitoring of the amount of ozone damage to forests is limited. We tested whether high resolution measurements of leaf reflectance (between UV and Infrared, 350-2500nm) could be used to identify ozone stress in a range of broadleaf saplings under experimental conditions. CEH run an air pollution facility in North Wales with a series of greenhouse domes fumigated with difference concentrations of ozone, we grew saplings for 6 months in these domes while taking regular reflectance and physiology measurements. We found that the hyperspectral reflectance of saplings exposed to higher ozone concentrations differed significantly from saplings exposed to lower concentrations. The green reflectance peak, red edge and a peak in the short wavelength infrared all changed significantly with ozone treatment. Some classic vegetation indices such as MCARI also captured ozone stress, as well as the new index we defined using pairwise correlation analysis: OzDI, the normalised difference of wavelengths 2204nm and 2248nm.

This is an exciting first step in developing a way of measuring ozone stress in forests remotely, stay tuned for the next trial of this technique in adult trees. 

NERC Field Spectroscopy Facility provided loan of the spectrometers used in this research, they support UK environmental scientists with a pool of state-of-the-art spectroscopy instruments as well as training courses.