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

ABSTRACT

The effects of current and future elevated O3 concentrations (e[O3]) were investigated by a meta-analysis for poplar, a widely distributed genus in the Northern Hemisphere with global economic importance. Current [O3] has significantly reduced CO2 assimilation rate (Pn) by 33% and total biomass by 4% in comparison with low O3 level (charcoal-filtered air, CF). Relative to CF, an increase in future [O3] 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[O3], with feedback implications in reducing the formation of secondary air pollutants including O3. Reduced stomatal conductance and lower foliar area might increase runoff and freshwater availability in O3 polluted areas. Higher cumulated O3 exposure over a threshold of 40 ppb (AOT40) induced larger reductions in Pn, total biomass and isoprene emission. Relationships of light-saturated photosynthesis rates (Asat), total biomass and chlorophyll content with AOT40 using a global dataset are provided. These relationships are expected to improve O3 risk assessment and also to support the inclusion of the effect of O3 in models addressing plantation productivity and carbon sink capacity.