Ozone impacts on vegetation in a nitrogen enriched and changing climate

This paper provides a process-oriented perspective on the combined effects of ozone (O₃), climate change and/or nitrogen (N) on vegetation. Whereas increasing CO₂ in controlled environments or open-top chambers often ameliorates effects of O₃ on leaf physiology, growth and C allocation, this is less likely in the field. Combined responses to elevated temperature and O₃ have rarely been studied even though some critical growth stages such as seed initiation are sensitive to both. Under O₃ exposure, many species have smaller roots, thereby enhancing drought sensitivity. Of the 68 species assessed for stomatal responses to ozone, 22.5% were unaffected, 33.5% had sluggish or increased opening and 44% stomatal closure. The beneficial effect of N on root development was lost at higher O₃ treatments whilst the effects of increasing O₃ on root biomass became more pronounced as N increased. Both responses to gradual changes in pollutants and climate and those under extreme weather events require further study. - Highlights: • CO₂ amelioration of O₃ effects on leaf physiology are less likely in the field. • Both extremes of temperature and O₃ impact on critical growth stages. • Many species are more sensitive to drought as a result of exposure to O₃ pollution. • The beneficial effect of N on root development is lost at higher O₃ treatments. • The effects of O₃ on root biomass are higher at high than low N. - A process-oriented perspective on the combined effects of ozone, climate change and/or nitrogen on vegetation.