From ozone depletion to re-defining PAR and to climate change

Stemming from my background in studies concerning plant responses to UV radiation, I wanted to highlight the news about the recovery of the ozone layer. Please take a look at the article After 30 years of protecting the ozone layer, some reasons to be cheerful, written by Nigel Paul, Professor of Plant Science at the Lancaster University and co-chair of the United Nations Environment Programme (UNEP) panel on ozone depletion.

During the days of most extensive research related to ozone depletion and increasing levels of UV-B radiation, mainly the harmful effects were considered. Nowadays UV studies have taken great steps forward, looking beyond ozone depletion. Recently the UV-B induced morphological effects have been elucidated and e.g. the need for understanding of the UV-B dose–response underpinning morphogenesis was demonstrated by Matthew Robson et al. in the review Re-interpreting plant morphological responses to UV-B radiation. Jason Wargent and Brian Jordan summarize the multifaceted roles of UV-B radiation in their review From ozone depletion to agriculture: understanding the role of UV radiation in sustainable crop production: “Indeed, it could be argued that UV radiation acts as a ubiquitous, albeit energetic, cue in the regulation of typical plant development, as opposed to a consistent inducer of damage”.

Attention has been drawn also to the definition of photosynthetically active radiation (PAR) itself. Commonly accepted definition is 400-700nm, challenged with good reason by Turnbull et al. Photosynthetic benefits of ultraviolet-A to Pimelea ligustrina, a woody shrub of sub-alpine Australia. Opposite end of the spectrum needs to be considered here too, as demonstrated by Pettai et al. The long-wavelength limit of plant photosynthesis, measuring a detectable O₂ evolution remaining till 780 nm in sunflower leaves. Using the current PAR limits may lead to underestimation of photosynthetic carbon gain, as pointed out by Turnbull et al., that in turn can affect the outcome of climate change scenarios through source-sink estimations!

Picture above shows sun spectral energy irradiance reaching ground, highlighting different wavebands (UV-B 280-315nm, UV-A 315-400nm, PAR 400-700nm, far-red 700-750nm). Picture drawn with R, using photobiology packages developed by Pedro J. Aphalo.

And finally, despite the promising news about the recovery, ozone depletion can not yet be overlooked. This is demonstrated by Williamson et al., emphasizing the interactions between the drivers of climate change and ozone depletion, and the feedbacks among climate, ozone and UV: Solar ultraviolet radiation in a changing climate.