Extreme Heat Event Alters BVOC Responses to Elevated Ozone: From Physiology to Emission Patterns

Extreme heat and elevated ozone (O3) significantly affect plant growth and secondary metabolism, including biogenic volatile organic compound (BVOC) emissions. However, the impact of the extreme heat events (EHs) on the O3-induced BVOC emissions remains unclear. Here, Quercus nuttallii(an isoprene emitter) and Q. acutissima (a monoterpene emitter) were exposed to five O3 treatments for three months and subjected to a two-week EH. The emission rates of isoprene and monoterpenes, their synthesis capacities, and reactive oxygen species (ROS) levels were determined to investigate how heat stress modulates O3 effects. Both BVOC types showed a hormetic response to O3, with low doses of O3 stimulating emissions and high doses suppressing them. Isoprene (Hedges'g = 2.91) and monoterpene (Hedges'g = 2.52) emission rates were inhibited by short-term EH across the five O3 treatments. However, isoprene emission rates generally recovered during the post-EH period, except under the highest O3 exposure (NF80). EH also shifted isoprene's response to O3 from being synthesis-driven to ROS-driven. Although the monoterpene emission rate response to O3 was driven by synthesis capacity in the pre-EH period, this response became less explainable by either factor post-EH. These findings emphasize the profound effects of EH on the BVOC response to O3, providing crucial insights for predicting regional BVOC emissions under future climate scenarios.