Process-based modelling of isoprene emission by oak leaves

The emission rate of the volatile reactive compound isoprene, emitted predo minantly by trees, must be known before the level of photo-oxidants produce d during summer smog can be predicted reliably. The emission is dependent o n plant species and local conditions, and these dependencies must be quanti fied to be included in any empirical algorithm for the calculation of isopr ene production. Experimental measurements of isoprene emission rates are ex pensive, however, and existing data are scarce and fragmentary, To overcome these difficulties, it is promising to develop a numerical model capable o f precisely calculating the isoprene emission by trees for diverse ecosyste ms, even under changing environmental conditions, A basic process-based bio chemical isoprene emission model (BIM) has therefore been developed, which describes the enzymatic reactions in leaf chloroplasts leading to the forma tion of isoprene under varying environmental conditions (e.g. light intensi ty, temperature). Concentrations of the precursors of isoprene formation, 3 -phosphoglyceric acid and glyceraldehyde 3-phosphate, are provided by a pub lished light fleck photosynthesis model. Specific leaf and enzyme parameter s were determined for the pedunculate oak (Quercus robur L.), so that the B IM is capable of calculating oak-specific isoprene emission rates as influe nced by the leaf temperature and light intensity. High correlation was obse rved between isoprene emission rates calculated by the BIM and the diurnal isoprene emission rates of leaves measured under controlled environmental c onditions. The BIM was even capable of describing changes in isoprene emiss ion caused by midday depression of net photosynthesis.