Sensitivity of isoprene emission rate to ozone in greening trees is concurrently determined by isoprene synthesis capacity and stomatal conductance.

The sensitivity of isoprene emission rate (ISO) to ozone (O) in plant suggests potentially large changes in future isoprene emissions, which will have important consequences for atmospheric chemistry. However, the interspecific variation of ISO sensitivity to O and its key drivers remain largely unknown. In this study, four urban greening tree species were exposed to two O treatments (charcoal-filtered air, CF; and non-filtered ambient air plus 60 ppb extra O, EO) in open-top chambers for one growing season. We aimed to compare the interspecific variation in O inhibitory effect on ISO and explore its physiological mechanism. EO decreased the ISO by on average 42.5 % across species. According to absolute effect size ranking, the highest ISO sensitivity to EO was observed in Salix matsudana, followed by Sophora japonica and hybrid poplar clone '546', while Quercus mongolica ISO was the least sensitive. Leaf anatomical structures differed in tree species but did not respond to EO. Furthermore, the ISO sensitivity to O was driven by the concurrent effects of O on ISO synthesis ability (i.e., dimethylallyl diphosphate and isoprene synthase contents) and stomatal conductance. Overall, the mechanistic understanding grained from this study may promote the integrity of O effect into process-based ISO emission models.