Elevated CO2 negates O3 impacts on terrestrial carbon and nitrogen cycles

Increasing tropospheric concentrations of ozone (e[O-3]) and carbon dioxide (e[CO2]) profoundly perturb terrestrial ecosystem functions through carbon and nitrogen cycles, affecting beneficial services such as their capacity to combat climate change and provide food. However, the interactive effects of e[O-3] and e[CO2] on these functions and services remain unclear. Here, we synthesize the results of 810 studies (9,109 observations), spanning boreal to tropical regions around the world, and show that e[O-3] significantly decreases global net primary productivity and food production as well as the capacity of ecosystems to store carbon and nitrogen, which are stimulated by e[CO2]. More importantly, simultaneous increases in [CO2] and [O-3] negate or even overcompensate the negative effects of e[O-3] on ecosystem functions and carbon and nitrogen cycles. Therefore, the negative effects of e[O-3] on terrestrial ecosystems would be overestimated if e[CO2] impacts are not considered, stressing the need for evaluating terrestrial carbon and nitrogen feedbacks to concurrent changes in global atmospheric composition.