Modeling of annual variations of oak (Quercus robur L.) isoprene synthase activity to predict isoprene emission rates

Isoprene plays an important role in regulating the atmospheric trace gas co mposition, in particular the tropospheric ozone concentrations. Therefore r ealistic estimates of the seasonal variation of isoprene emission source st rengths of strong isoprene-emitting deciduous trees such as pedunculate oak (Quercus robur L.) are required in temperate regions of Europe. In 1995 to 1997 a study was conducted to survey the annual fluctuations of oak isopre ne synthase activity and photosynthetic pigment contents, the latter as a p arameter for the development of the photosynthetic apparatus of oak leaves. Depending on annual temperature and light profiles (photosynthetic photon flux densities (PPFD)), different seasonal patterns of isoprene synthase ac tivity were observed with maximum activities of 18.4 +/- 10.6 nmol m(-2),14 .1 +/- 5.8 nmol m(-2) s(-1), and 19.9 +/- 7.9 nmol m(-2) s-(1) in 1995, 199 6, and 1997, respectively. On the basis of isoprene synthase activity, chlo rophyll a measurements, and phenological data collected from pedunculate oa ks of 89 ecological regions covering all of Germany a model was developed f or the calculation of the seasonal variation of oak isoprene synthase activ ity in relation to annual fluctuation of temperature and PPFD. By coupling this model to a numeric process-based isoprene emission model it was possib le to predict isoprene emission rates of individual pedunculate oak trees w ith a deviation of 55%.