A process-based model to predict the effects of climatic change on leaf isoprene emission rates

A process-based model was constructed around the current knowledge of the biochemical pathway of isoprene synthesis, with the objective of producing a new model of high mechanistic content to simulate the effects of environmental change on rates of isoprene emission, and thus enable the prediction of emission rates under future climates. The model was based on the three potentially limiting processes underlying isoprene synthesis: pyruvate supply to provide the substrate of isoprene carbon, supply of adenosine triphosphate (ATP) for phosphorylation to dimethylallyl pyrophosphate (DMAPP), and the rate of isoprene synthesis from DMAPP, which was controlled by the temperature dependency of the enzyme isoprene synthase. Using mechanistic methods wherever possible, model simulations predicted the relative effects of changing photon flux density, carbon dioxide concentrations and temperature on leaf isoprene emission rates. The model was used to predict the interactive effects of elevated concentrations of carbon dioxide and temperature on rates of isoprene emission. Simulations indicated that the effects of carbon dioxide and temperature on isoprene emission rates were complicated by the interactive effects of two of the controlling rate-limiting processes in the synthesis of isoprene, namely phosphorylation rates and isoprene synthase activity. Under present concentrations of carbon dioxide and at photon flux density levels above ca. 500 μmol m−2 s−1 the controlling rate process is the temperature dependency of isoprene synthase.