Testing UV-B radiation as a proposed driver behind the end-Permian biotic crisis

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The ozone layer plays a vital role in intercepting harmful solar ultraviolet-B radiation (UV-B) from reaching Earth's surface. However, its effectiveness in doing so has fluctuated in the past and little is known of the impacts of a thinning ozone layer on vegetation. Anticipating potential consequences in the future depends on understanding time intervals with heightened UV stress in the past. The largest mass extinction in history at the end of the Permian Period (~252 million years ago) may have been one of these time intervals. Plant fossil records from this crisis show two odd features worldwide. Many pollen grains produced by vanishing woodland seed plants were malformed, and proliferating herbaceous plants (lycopsids) spread their spores frequently as unseparated clusters of four. Heightened UV exposure is hypothesized to have caused these abnormalities. Compounds produced by the largest volcanic province in history, the Siberian Traps, likely caused prolonged or frequent deterioration of the ozone shield. In this study researchers will test if high UV-B radiation levels could indeed explain the abnormalities and extinction patterns in plants observed during the end-Permian biotic crisis. This research is important to society because it will assess whether future activities weakening the ozone layer could destabilize forest ecosystems through reproductive failure of economically important groups of plants. Outreach from this work will raise public awareness of environmental changes in the past through developing a publicly accessible educational exhibit and web-module on ecosystems and extinctions of the Paleozoic Era.Using growth chamber and germination experiments, the researchers will determine whether elevated UV-B exposure triggers similar malformations in pollen and spores as observed in the fossil record, and whether this may lead to contrasting reproductive success between the tested living relatives of plant groups impacted by the crisis. They hypothesize high levels of UV-B will have a negative effect on conifer reproduction, but not severely affect fertility in lycopsids. In addition, they will also investigate whether UV-induced developmental responses appeared during times of active volcanism at its very source. For this, they will analyze end-Permian fossil pollen and spore assemblages from sediments within the Siberian Traps. Using observations in combination with a contemporary ecological experimental approach is a novel approach which will test an important hypothesis in paleoecology and may lend insight into species response under contemporary abiotic stressors.