Isoprene is the most important biogenic organic volatile compound emitted by terrestrial vegetation into the atmosphere, in term of amount and effects on atmospheric chemistry. Primary environmental drivers of isoprene production are photosynthetic photon flux density (PPFD), leaf temperature (T) and internal CO2 concentration (Ci). Robust process-based modelling approaches are needed to assess how future changes in these environmental drivers may affect isoprene emissions and consequently atmospheric chemistry, air quality and (indirectly) the radiative forcing of climate.
I present an original, conceptually simple model for isoprene emission by plants based on the hypothesis that the electron flux available for isoprene biosynthesis depends on the balance between the supply of reducing power generated by the light reactions of photosynthesis and the demand for reducing power in carbon fixation and photorespiration. I explain the physiological reasoning that led me to propose this.
Using various leaf-scale measurements of carbon assimilation and isoprene emission, including a laboratory study I conducted on black poplar, I show that the model can reproduce well the variations of isoprene emission with PPFD, temperature, and Ci. The model also reproduces the tendency for the fraction of carbon re-emitted as isoprene to increase with increasing PPFD, and for the quantum efficiency of isoprene emission to decrease with increasing CO2 concentration. The model is shown to systematically outperform mo§dels that are in common use today.
I also analysed the PPFD and temperature responses of carbon assimilation and isoprene emission as measured above the forest canopy. The model was upscaled and shown to reproduce key responses shown in two long-term flux monitoring datasets from temperate mixed forests. I discuss future research needs and the potential for this model to be further scaled up for global analyses.Open Acces
