Detecting long-term metabolic shifts using isotopomers: CO2-driven suppression of photorespiration in C3 plants over the 20th century

Decadal-scale metabolic responses of plants to environmental changes, including the magnitude of the "CO₂ fertilization" effect, are a major knowledge gap in Earth system models, in agricultural models, and for societal adaptation. We introduce intramolecular isotope distributions (isotopomers) as a methodology for detecting shifts in plant carbon metabolism over long times. Trends in a deuterium isotopomer ratio allow quantification of a biogeochemically relevant shift in the metabolism of C₃ plants toward photosynthesis, driven by increasing atmospheric CO₂ since industrialization. Isotopomers strongly increase the information content of isotope archives, and may therefore reveal long-term acclimation or adaptations to environmental changes in general. The metabolic information encoded in isotopomers of plant archives bridges a fundamental gap between experimental plant science and paleoenvironmental studies.