Abstract
Considerable amounts and varieties of biogenic volatile organic compounds (BVOCs) are exchanged between vegeta-tion and the surrounding air. These BVOCs play key ecological and atmospheric roles that must be adequately repre-sented for accurately modeling the coupled biosphere–atmosphere–climate earth system. One key uncertainty inexisting models is the response of BVOC fluxes to an important global change process: drought. We describe the diur-nal and seasonal variation in isoprene, monoterpene, and methanol fluxes from a temperate forest ecosystem before,during, and after an extreme 2012 drought event in the Ozark region of the central USA. BVOC fluxes were domi-nated by isoprene, which attained high emission rates of up to 35.4 mg m2h1at midday. Methanol fluxes werecharacterized by net deposition in the morning, changing to a net emission flux through the rest of the daylight hours.Net flux of CO2reached its seasonal maximum approximately a month earlier than isoprenoid fluxes, which high-lights the differential response of photosynthesis and isoprenoid emissions to progressing drought conditions. Never-theless, both processes were strongly suppressed under extreme drought, although isoprene fluxes remainedrelatively high compared to reported fluxes from other ecosystems. Methanol exchange was less affected by droughtthroughout the season, confirming the complex processes driving biogenic methanol fluxes. The fraction of daytime(7–17 h) assimilated carbon released back to the atmosphere combining the three BVOCs measured was 2% of grossprimary productivity (GPP) and 4.9% of net ecosystem exchange (NEE) on average for our whole measurement cam-paign, while exceeding 5% of GPP and 10% of NEE just before the strongest drought phase. TheMEGANv2.1 modelcorrectly predicted diurnal variations in fluxes driven mainly by light and temperature, although further research isneeded to address model BVOC fluxes during drought events.
