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 b iochemical pathway of isoprene synthesis, with the objective of producing a new model of high mechanistic content to simulate the effects of environme ntal change on rates of isoprene emission, and thus enable the prediction o f emission rates under future climates. The model was based on the three po tentially limiting processes underlying isoprene synthesis: pyruvate supply to provide the substrate of isoprene carbon, supply of adenosine triphosph ate (ATP) for phosphorylation to dimethylallyl pyrophosphate (DMAPP), and t he rate of isoprene synthesis from DMAPP, which was controlled by the tempe rature dependency of the enzyme isoprene synthase. Using mechanistic method s wherever possible, model simulations predicted the relative effects of ch anging photon flux density, carbon dioxide concentrations and temperature o n leaf isoprene emission rates. The model was used to predict the interacti ve effects of elevated concentrations of carbon dioxide and temperature on rates of isoprene emission. Simulations indicated that the effects of carbo n dioxide and temperature on isoprene emission rates were complicated by th e interactive effects of two of the controlling rate-limiting processes in the synthesis of isoprene, namely phosphorylation rates and isoprene syntha se activity. Under present concentrations of carbon dioxide and at photon f lux density levels above ca. 500 mu mol m(-2) s(-1) the controlling rate pr ocess is the temperature dependency of isoprene synthase. (C) 2000 Elsevier Science B.V. All rights reserved.