Department of Earth System Science, University of California, Irvine, CA, 92697, USA.
Institute of Meteorology and Geophysics, University of Innsbruck, Innsbruck, Austria.
Glob Chang Biol. 2015 Oct;21(10):3657-74. doi: 10.1111/gcb.12980. Epub 2015 Jul 7.
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.
大量且多样的生物源挥发性有机化合物（BVOC）在植被和周围空气之间进行交换。这些 BVOC 在生态和大气中发挥着关键作用，为准确模拟耦合的生物圈-大气-气候地球系统，这些作用必须得到充分体现。现有模型中的一个关键不确定性因素是 BVOC 通量对一个重要的全球变化过程的响应：干旱。我们描述了美国中部分区奥沙克地区 2012 年极端干旱事件前后，一个温带森林生态系统中异戊二烯、单萜和甲醇通量的日变化和季节变化。BVOC 通量主要由异戊二烯主导，其在中午达到高达 35.4mg m(-2) h(-1)的高排放速率。甲醇通量的特征是在早晨净沉积，在其余的日光时间内转变为净排放通量。CO2 的净通量在达到其季节最大值时，比异戊二烯通量早约一个月，这突出了光合作用和异戊二烯排放对干旱条件的不同响应。然而，这两个过程在极端干旱条件下都受到强烈抑制，尽管与其他生态系统报告的通量相比，异戊二烯通量仍然相对较高。整个季节中，干旱对甲醇交换的影响较小，这证实了驱动生物源甲醇通量的复杂过程。结合三种测量的 BVOC，白天（7-17 小时）同化碳中释放回大气的部分占总初级生产力（GPP）的 2%，净生态系统交换（NEE）的 4.9%，而在最强干旱阶段之前，GPP 超过 5%，NEE 超过 10%。meganv2.1 模型正确预测了主要由光照和温度驱动的通量的日变化，尽管需要进一步研究来解决模型在干旱事件期间的 BVOC 通量问题。
