Changes in chiral monoterpenes during drought in a rainforest reveal distinct source mechanisms
- 1Max Planck Institute for Chemistry, Atmospheric Chemistry, Mainz, Germany
- 2Chair of Ecosystem Physiology, University Freiburg, Freiburg, Germany
- 3School of Chemistry, University of Edinburgh, Edinburgh, UK
- 4UK Centre for Ecology & Hydrology, Edinburgh, UK
- 5Biosphere 2, University of Arizona, Oracle, USA
- 6Honors College, University of Arizona, Tucson, USA
- 7School of Natural Resources and the Environment, University of Arizona, Tucson, USA
- 8Climate and Atmosphere Research Center, The Cyprus Institute, 1645 Nicosia, Cyprus
- 9Department of Environmental Sciences, University of Basel, Basel, Switzerland
Monoterpenes (C10H16) are emitted in large quantities by vegetation to the atmosphere (>100 TgC year−1), where they readily react with hydroxyl radicals and ozone to form new particles and, hence, clouds, affecting the Earth’s radiative budget and, thereby, climate change[1-3]. Although most monoterpenes exist in two chiral mirror-image forms termed enantiomers, these (+) and (−) forms are rarely distinguished in measurement or modelling studies[4-6]. Therefore, the individual formation pathways of monoterpene enantiomers in plants and their ecological functions are poorly understood. Here we present enantiomerically separated atmospheric monoterpene and isoprene data from an enclosed tropical rainforest ecosystem in the absence of ultraviolet light and atmospheric oxidation chemistry, during a four-month controlled drought and rewetting experiment, the Biosphere 2 Water, Air and Life Dynamics campaign (B2WALD) in 2019[7, 8]. The measurements were obtained with an on-line gas chromatograph-mass spectrometer over five time periods: pre-drought, early drought, severe drought, deep rewet and rain rewet.
Surprisingly, the emitted enantiomers showed distinct diel emission peaks, which responded differently to progressive drying. Isotopic labelling established that vegetation emitted mainly de novo-synthesized (−)-α-pinene, whereas (+)-α-pinene was emitted from storage pools. As drought progressed, the source of (−)-α-pinene emissions shifted to storage pools which would favour cloud formation since the peak concentration became more aligned with temperature. Pre-drought mixing ratios of both α-pinene enantiomers correlated better with other monoterpenes than with each other, indicating different enzymatic controls. These results show that enantiomeric distribution is key to understanding the underlying processes driving monoterpene emissions from forest ecosystems and predicting atmospheric feedbacks in response to climate change.
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How to cite: Byron, J., Kreuzwieser, J., Purser, G., van Haren, J., Ladd, S. N., Meredith, L., Werner, C., and Williams, J.: Changes in chiral monoterpenes during drought in a rainforest reveal distinct source mechanisms, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13774, https://doi.org/10.5194/egusphere-egu24-13774, 2024.
