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

Abstract

Concentration- and flux-based O3 dose-responses of isoprene emission from single leaves and whole plants were developed. Two poplar clones differing in O3 sensitivity were exposed to five O3 levels in open-top chambers for 97d: charcoal-filtered ambient air (CF), non-filtered ambient air (NF) and NF plus 20ppb (NF+20), 40ppb (NF+40) and 60ppb (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 O3 concentrations >40ppb) and flux-based indices (PODY , cumulative stomatal uptake of O3 >Y nmol O3 m-2 PLA s-1 ). AOT40- and POD7 -based dose-responses performed equally well. The two clones responded differently to AOT40 and similarly to PODY (with a slightly higher R2 for POD7 ) when the emission was expressed as change relative to clean air. We thus recommend POD7 as a large-scale risk assessment metric to estimate isoprene emission responses to O3 in poplar.