PS 64-75
Does accounting for adaptation to local climate reduce the gap between models and observations in predicting future isoprene emission loads into the atmosphere?
Isoprene emission from the vegetation is an important biosphere-atmosphere interaction and a key constraint to the chemical properties of the troposphere. Isoprene reactions can contribute to ozone formation and indirectly affect greenhouse gas accumulation. Isoprene synthesis is controlled by isoprene synthase, while subsequent emission is affected by the physical environment and altered by exposure to environmental stress. It has been hypothesized that a warmer climate, as a consequence of global warming may enhance isoprene emissions with mostly positive feedbacks to warming, but there are no reliable quantitative estimates, as the underlying processes are not understood. Current semi-empirical emission models often underestimate observed emission rates, as they fail to account for many of the physiological, biochemical and adaptive constraints over the synthesis and emission of isoprene. To resolve the gap between model estimates and measured rates, we compared the response of two dominant oak species (pin-, Quercus palustris and post oak, Q. stellata) in north-west Missouri to increasing summer temperatures in a field study in 2013. Data demonstrate, that accounting for the adaptive capacity of native species to increasing temperatures in regional emission models, narrows the gap between observations and modelled regional emission rates, allowing for better estimation of future emissions.
Results/Conclusions
Isoprene emission of south-facing, sun exposed leaves at 2-4 m canopy height of each species was measured biweekly in a controlled-environment cuvette enclosure during the summer of 2013. Basal isoprene emission rates (at 30°C and 1000 µmolm-2s-1 PAR) and emission rates at stepwise increasing temperatures from 30°C to 50°C were sampled from the cuvette outflow concentrating the air onto adsorbents. Samples were analysed by GC-MS. Isoprene emission rates were correlated with measured local climate parameters. Preliminary results show that isoprene emission response to increasing temperatures in both oak species indicated a shift to higher capacities for isoprene emission at extreme temperatures, exceeding current model predictions (350 µg C g-1 h-1 measured versus model estimate of 225 µg C g-1 h-1 emitted isoprene at 50°C). Calculations indicate a 3-7°C shift in the isoprene emission optimum for this species as compared to model estimates. These data are in good correlation with our recent observations in a study performed in Texas, suggesting that native emitter species respond to high temperatures with an increased capacity for isoprene emission at higher temperatures, attributed to the evolution of a more thermo-tolerant isoprene synthase enzyme, as a result of their adaptation to the local climate.