Acute and chronic ozone exposure temporarily affects seed germination in alpine plants

This study was the first to investigate the direct effects of anomalous concentrations of ozone mediated by summer heat waves on seed germination in alpine plants. During germination, the seeds were exposed to three peaks of O3 concentration (125 ppb for 5 and 10 days; 185 ppb for 5 days), derived from measurements taken close to the species growing site. High O3 concentration delayed the first germination time, increased the mean germination time, and reduced the germination percentage during and immediately after the treatment, but, in most cases, effects were weak and had almost vanished three weeks after the treatments. In few cases, chronic exposure to O3 (125 for 10 days’ treatment) enhanced seed germination compared to the control, suggesting that ozone may induce antioxidant and DNA-repair mechanisms or dormancy-breaking effects in hydrated seeds. Although seed mortality increased during O3 treatments in four species, the effect of O3 on seed germination is mostly limited to the period of exposure, indicating that it is unlikely to produce permanent negative effects on seeds, during the germination phase. Our results show that the direct effect of O3 on seeds of alpine plants may have minor impacts on plant reproductive performance during seed germination.