Modulating effects of temperature on CO2-inhibited isoprene emissions in Eucalyptus urophylla

Terrestrial vegetation emits substantial amounts of highly reactive isoprene, significantly impacting atmospheric chemistry and climate change. Both atmospheric carbon dioxide (CO 2 ) concentration and temperature can influence plant isoprene emissions; however, whether these factors have a synergistic effect remains unclear, particularly for tropical/subtropical plants. In this study, we conducted in-situ controlled experiments on Eucalyptus urophylla , a representative tropical/subtropical species, to investigate the seasonal variation in the response of isoprene emissions to CO 2 concentrations (ISOP-CO 2 response) and to identify potential controlling factors. The results showed that high CO 2 exerts a nearly linear inhibitory effect on isoprene emissions, as indicated by the slope of the ISOP-CO 2 response curve. This inhibitory effect exhibited evident seasonal changes, with stronger suppression during cooler seasons and weaker suppression during warmer seasons. This finding contrasts with the default ISOP-CO 2 response in the MEGAN model, which ignored seasonal variation. Further analysis showed a significant correlation between the slope of the ISOP-CO 2 response curve and growth temperature from the past 10 days, indicating that these metrics are effective indicators for predicting seasonal changes. Our findings reveal a synergistic mechanism between temperature and CO 2 concentration effects on isoprene emissions. By coupling the effects of growth temperature with the ISOP-CO 2 response, this mechanism can be integrated into models to provide more accurate predictions of future isoprene emissions, reducing prediction biases, especially during cooler seasons.