Heatwaves favour acyclic monoterpene emissions in tropical forests.

Heatwaves perturb plant physiology and monoterpene emissions, with important consequences for atmospheric chemistry and climate. Acyclic and cyclic monoterpenes differ markedly in their chemical reactivity, biosynthetic pathways, physiological functions, and atmospheric impacts, yet their heatwave responses remain poorly quantified, and current emission models generally assign them similar temperature sensitivities. Here, we combine leaf warming experiments, heatwave observations, and temperature-response modeling to show that acyclic monoterpenes from tropical trees in South China possess substantially higher temperature sensitivity than cyclic forms. As a result, heatwaves shift ambient mixture toward acyclic compounds, which approach half of measured monoterpenes and dominate calculated ozone and hydroxyl-radical reactivity. Default temperature algorithms in current emission models fail to reproduce this cyclic-to-acyclic shift, whereas the revised temperature functions developed here successfully capture the observed increase in acyclic fraction. Climate extremes may therefore alter atmospheric chemistry not only by changing monoterpene abundance, but also by reshaping monoterpene composition.