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

The effects of current and future elevated O-3 concentrations (e[O-3]) were investigated by a meta-analysis for poplar, a widely distributed genus in the Northern Hemisphere with global economic importance. Current [O-3] has significantly reduced CO2 assimilation rate (P-n) by 33% and total biomass by 4% in comparison with low O-3 level (charcoal-filtered air, CF). Relative to CF, an increase in future [O-3] 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-3], with feedback implications in reducing the formation of secondary air pollutants including O-3 . Reduced stomatal conductance and lower foliar area might increase runoff and freshwater availability in O-3 polluted areas. Higher cumulated O-3 exposure over a threshold of 40 ppb (AOT40) induced larger reductions in P-n, total biomass and isoprene emission. Relationships of light-saturated photosynthesis rates (A(sat)), total biomass and chlorophyll content with AOT40 using a global dataset are provided. These relationships are expected to improve O-3 risk assessment and also to support the inclusion of the effect of O-3 in models addressing plantation productivity and carbon sink capacity. (C) 2018 Elsevier B.V. All rights reserved.