A model coupling foliar monoterpene emissions to leaf photosynthetic characteristics in Mediterranean evergreen Quercus species

A model was developed and parameterized to simulate monoterpene emission rates per unit leaf area (E) dependent on foliar photosynthetic potentials and activity of monoterpene synthases in the evergreen sclerophylls Quercus coccifera L. and Q. ilex L. Assuming that total activity of monoterpene synthases controls the pathway flux, the product of leaf dry mass per unit area E was culculated as the fraction of total electron flow used for monoterpene synthesis (epsilon), the rate of photosynthetic electron transport (J) per unit leaf dry mass and the reciprocal of the electron cost of monoterpene synthesis. In the model, light effects on E result from light responses of J, and the temperature relationship of E combines temperature dependencies of J and the specific activity of monoterpene synthase (S-S). Having determined J from leaf photosynthesis data and deriving an estimate of S-S from in vitro laboratory measurements, good fits to diurnal time-courses of monoterpenoid emission rates were obtained using a single leaf-dependent coefficient, the total monoterpene synthase activity in the leaves. Our analysis demonstrates that using l as a surrogate of E leads to a realistic description of E, especially under stress conditions where the previous models fail. However, analysis of daily time courses of E indicated that storage of monoterpenoids in nonspecific leaf compartments might alter the correspondence between monoterpenoid synthesis and emission rates, especially after rapid environmental change.