Ozone impacts on vegetation in a nitrogen enriched and changing climate.

This paper provides a process-oriented perspective on the combined effects of ozone (O 3 ), climate change and/or nitrogen (N) on vegetation. Whereas increasing CO 2 in controlled environments or open-top chambers often ameliorates effects of O 3 on leaf physiology, growth and C allocation, this is less likely in the field. Combined responses to elevated temperature and O 3 have rarely been studied even though some critical growth stages such as seed initiation are sensitive to both. Under O 3 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 O 3 treatments whilst the effects of increasing O 3 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. [ABSTRACT FROM AUTHOR]