Modeling the temporal dynamics of monoterpene emission by isotopic labeling in Quercus ilex leaves

A mathematical model to study the temporal dynamics of stable isotope ¹³C incorporation into monoterpene molecules, emitted from Mediterranean evergreen sclerophyll oak Quercus ilex L. leaves, was developed. The box model uses leaf level gas exchange and monoterpene emission data to assess biochemical and diffusional processes of the light-dependent monoterpene biosynthesis and emission within the leaf tissues. We estimated total leaf monoterpene pool exchange half-lifes against these processes. The slowest response took up to 38 h, while the fastest response occurred within 1 h, taking the sum of the lumped processes time constants into account. Separately, the turnover half-lives of the biochemical processes ranged between 26 min up to more than 4 h. The diffusional processes turnover times, driven by the physico-chemical properties of the monoterpene molecule, have been found to range between 32 min and 3 h, depending on the number of ¹³C-labeled carbon atoms. As a consequence, the steady-state assumption that is used in many larger scale emission models, may not hold in all cases and the application of process-based algorithms is beneficial to overcome such long transient pool dynamics of light-dependent monoterpene emission.