Seasonal pattern of isoprene synthase activity in Quercus robur leaves and its significance for modeling isoprene emission rates

Biogenic emission of hydrocarbons plays an important role in the interactions between plants, especially trees, and the atmosphere. Among these volatile organic compounds isoprene (2-methyl-1,3-butadiene) is the predominant component emitted by many photosynthesizing leaves. Its rapid atmospheric breakdown substantially affects the oxidation potential of the atmosphere. An enzyme, isoprene synthase, extracted from leaves of European oak (Quercus robur L.) was previously found to catalyse the Mg(2+)-dependent elimination of diphosphate from dimethylallyidiphosphate to form isoprene. The present paper describes the seasonal variation of this enzyme acitivity in Quercus robur (L.) leaves in 1995.The enzymatic data obtained were used to create an additional term for the isoprene emission algorithm (ISOG93). The addition of this correction term for the seasonality of isoprene synthase to the emission model improved considerably the simulation of seasonal isoprene emission rates in oaks, avo iding over- and underestimations in the current modeling approach.