Decoding the CO2-stress interplay: A meta-analytical deep dive into isoprene and monoterpene emission dynamics across diverse plants.

Isoprene and monoterpene, as the dominant biogenic volatile organic compounds (BVOCs), play critical roles in atmospheric chemistry. However, the individual effect of elevated CO2 and its interactions with co-stressors (i.e., temperature, drought, and light) on BVOCs emissions remain insufficiently understood. This meta-analysis synthesizes 1658 datasets from global studies to explore how CO2 stress, both alone and in combination with temperature, drought, and light, modulates isoprene and monoterpene emissions across plant functional types and families. Key findings show that elevated CO2 alone suppresses isoprene emissions by 19.77-29.11 %, but increases them by 35.1 % under concurrent warming. In contrast, elevated CO2 alone inhibits monoterpene emissions by an average of 20.1 %, with further significant suppression (average 126.25 %) under combined CO2 and temperature or drought stress. Analyses along CO2 gradients further reveal that low concentrations promote isoprene emissions while high concentrations suppress them - a pattern inverse for monoterpene. Mechanistically, elevated CO2 enhances net assimilation rate (average +44.38 %) and intercellular CO2 concentration (average +36.59 %) in isoprene-emitting plants. Plant functional types and phylogeny critically modulate such responses. Broadleaf trees (e.g., Fagaceae, Salicaceae and Platanaceae) show pronounced isoprene suppression, whereas evergreen trees (e.g., Pinaceae) exhibit the strongest monoterpene suppression, mainly driven by divergent carbon allocation via two primary pathway - the methylerythritol phosphate (MEP) and mevalonic acid (MVA) pathways. This work elucidates key BVOCs-climate feedbacks and provides a scientific basis for designing aerosol-mitigation strategies in a changing climate.