You are here:
Ecosystem-scale VOC fluxes during an extreme drought in a broad-leaf temperate forest of the Missouri Ozarks (central USA)
Citation:
Seco, R., T. Karl, A. Guenther, K. Hosman, S. Pallardy, L. Gu, Chris Geron, P. Harley, AND S. Kim. Ecosystem-scale VOC fluxes during an extreme drought in a broad-leaf temperate forest of the Missouri Ozarks (central USA). GLOBAL CHANGE BIOLOGY. Blackwell Publishing, Malden, MA, 21(10):3657-74, (2015).
Impact/Purpose:
Biogenic volatile organic compounds (BVOCs) exchanged between vegetation and the atmosphere play key ecological and atmospheric roles, yet the ecosystem-level response of BVOC emissions to drought is uncertain. In 2012 we measured BVOC fluxes in an oak-dominated temperate forest of the central USA with the eddy covariance technique and found that BVOC emissions were dominated by high fluxes of isoprene. During an extreme drought event in summer, BVOC emissions were strongly suppressed although this decrease was not adequately simulated by existing BVOC emission models. Improving these BVOC models is needed for better forecasting of climate and air quality.
Description:
Considerable amounts and varieties of biogenic volatile organic compounds (BVOCs) are exchanged between vegetation and the surrounding air. These BVOCs play key ecological and atmospheric roles that must be adequately represented for accurately modeling the coupled biosphere-atmosphere-climate Earth system. One key uncertainty in existing models is the response of BVOC fluxes to an important global change process: drought. We describe the diurnal 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 dominated by isoprene, which attained high emission rates of up to 35.4 mg m-2 h-1 at midday. Methanol fluxes were characterized by net deposition in the morning, changing to a net emission flux through the rest of the daylight hours. Net flux of CO2 reached its seasonal maximum approximately a month earlier than isoprenoid fluxes, which highlights the differential response of photosynthesis and isoprenoid emissions to progressing drought conditions. Nevertheless, both processes were strongly suppressed under extreme drought, although isoprene fluxes remained relatively high compared to reported fluxes from other ecosystems. Methanol exchange was less affected by drought throughout 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 gross primary productivity (GPP) and 4.9 % of net ecosystem exchange (NEE) on average for our whole measurement campaign, while exceeding 5 % of GPP and 10 % of NEE just before the strongest drought phase. The MEGANv2.1 model correctly predicted diurnal variations in fluxes driven mainly by light and temperature, although further research is needed to address model BVOC fluxes during drought events.
