Concentration- and flux-based dose-responses of isoprene emission from poplar leaves and plants exposed to an ozone concentration gradient.

Concentration- and flux-based O dose-responses of isoprene emission from single leaves and whole plants were developed. Two poplar clones differing in O sensitivity were exposed to five O levels in open-top chambers for 97 d: charcoal-filtered ambient air (CF), non-filtered ambient air (NF) and NF plus 20 ppb (NF + 20), 40 ppb (NF + 40) and 60 ppb (NF + 60). At both leaf and plant level, isoprene emission was significantly decreased by NF + 40 and NF + 60 for both clones. Although intra-specific variability was found when the emissions were up-scaled to the whole plant, both leaf- and plant-level emissions decreased linearly with increasing concentration-based (AOT40, cumulative exposure to hourly O concentrations >40 ppb) and flux-based indices (POD , cumulative stomatal uptake of O  > Y nmol O m PLA s ). AOT40- and POD -based dose-responses performed equally well. The two clones responded differently to AOT40 and similarly to POD (with a slightly higher R for POD ) when the emission was expressed as change relative to clean air. We thus recommend POD as a large-scale risk assessment metric to estimate isoprene emission responses to O in poplar.