Rising temperatures and atmospheric CO2 exert complex, interacting effects on plant carbon metabolism and volatile organic compound (VOC) emissions. This study investigated the physiological mechanisms underlying acute thermal tolerance in Populus nigra by integrating leaf gas exchange with high-resolution proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOF-MS). We employed a factorial design (25–40 °C; 400 and 800 ppm CO2) to examine how metabolic regulation and pulse-induced signalling interact across thermal gradients. Our results identify a critical metabolic tipping point around 40 °C, representing a transition toward a survival-orientated state. Isoprene emission decoupled from net photosynthesis at this threshold; while carbon assimilation collapsed, isoprene was maintained at near-maximal rates to prioritize thylakoid thermal protection. Under moderate temperatures (25–35 °C), emission capacity scaled linearly with the chloroplastic DMADP pool, but this relationship broke down at 40 °C. Notably, elevated CO2 sustained the magnitude of stress-related “bursts” at the thermal limit, suggesting that increased carbon availability provides the metabolic stamina required to fuel emergency defence and fermentative pathways. These findings demonstrate that acute thermal exposure triggers a metabolic reconfiguration, shifting resources from growth-oriented processes toward survival-based stabilization mechanisms.
Miguel Portillo‐Estrada (Tue,) studied this question.