Current ambient and elevated ozone effects on poplar: A global meta-analysis and response relationships.

The effects of current and future elevated O concentrations (e[O]) were investigated by a meta-analysis for poplar, a widely distributed genus in the Northern Hemisphere with global economic importance. Current [O] has significantly reduced CO assimilation rate (P) by 33% and total biomass by 4% in comparison with low O level (charcoal-filtered air, CF). Relative to CF, an increase in future [O] would further enhance the reduction in total biomass by 24%, plant height by 17% and plant leaf area by 19%. Isoprene emissions could decline by 34% under e[O], with feedback implications in reducing the formation of secondary air pollutants including O. Reduced stomatal conductance and lower foliar area might increase runoff and freshwater availability in O polluted areas. Higher cumulated O exposure over a threshold of 40 ppb (AOT40) induced larger reductions in P, total biomass and isoprene emission. Relationships of light-saturated photosynthesis rates (A), total biomass and chlorophyll content with AOT40 using a global dataset are provided. These relationships are expected to improve O risk assessment and also to support the inclusion of the effect of O in models addressing plantation productivity and carbon sink capacity.