A model analysis of the effects of nonspecific monoterpenoid storage in leaf tissues on emission kinetics and composition in Mediterranean sclerophyllous Quercus species -: art. no. 1110

[1] Although monoterpenoid-emitting Quercus species lack specific terpene storage structures, they may store monoterpenoids in nonspecific leaf compartments. To determine whether such storage may influence emission responses to diurnal changes in environmental factors, a dynamic emission model including "fast'' and "slow'' storage pools in parallel was constructed. Existence of two storage pools was inferred from the circumstance that monoterpene efflux from darkened leaves was poorly described by single-exponential decay relationship, but was well parameterized by double exponentials. Simulations indicated that nonspecific terpenoid storage may significantly alter daily monoterpenoid emission both at leaf and canopy scales. The model also described shifts in fractional monoterpenoid composition after changes in environmental factors that cannot be explained by current algorithms. Time constants for the "fast'' pool were negatively associated with monoterpenoid equilibrium gas/ water partition coefficient (H), suggesting that the "fast'' pool is in leaf liquid phase. The time constants for the "slow'' pool were independent of H, but scaled positively with monoterpenoid octanol/water partition coefficient, indicating that this pool is in lipid phase. Based on tentative pool locations and monoterpenoid physico-chemical characteristics, time constants of various pools were computed using a flow/conductance model. Although the time constants were correlated, the theoretical estimates were larger than those derived empirically. Nonhomogeneous monoterpenoid distribution, aggregation within leaf liquid phase, and adsorption to apoplast surfaces that all decrease the area for diffusion and decrease the effective diffusion coefficients likely explain this discrepancy. We conclude that physico-chemical models are needed to parameterize nonspecific storage effects on monoterpene emission dynamics and emission composition.