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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2017-260
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2017-260
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 04 Jul 2017

Submitted as: research article | 04 Jul 2017

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This discussion paper is a preprint. It has been under review for the journal Biogeosciences (BG). The manuscript was not accepted for further review after discussion.

13C labelling study of constitutive and stress-induced terpenoide missions from Norway spruce and Scots pine

Cheng Wu1, Iida Pullinen1,2, Stefanie Andres1, Astrid Kiendler-Scharr1, Einhard Kleist3, Andreas Wahner1, Jürgen Wildt1,3, and Thomas F. Mentel1 Cheng Wu et al.
  • 1Institute for Energy and Climate Research (IEK-8), Forschungszentrum Jülich, Jülich, Germany
  • 2Department of Applied Physics, University of Eastern Finland, Kuopio, Finland
  • 3Institute for Bio- and Geosciences (IBG-2), Forschungszentrum Jülich, Jülich, Germany

Abstract. Due to their large source strengths, biogenic volatile organic compounds (BVOCs) are important for atmospheric chemistry. Terpenoids, mainly consisting of isoprene, monoterpenes and sesquiterpenes, are the dominant BVOC class. There are two general mechanisms for their emissions: emissions directly from de novo biosynthesis (de novo emissions) and emissions from organs wherein the terpenoids are stored (pool emissions). While isoprene emissions are pure de novo emissions, the mechanism for monoterpene and sesquiterpene emissions is not always distinct. In particular, conifers have large storage pools and both mechanisms may contribute to the emissions.

To obtain more insight into the mechanisms of the terpenoid emissions from Eurasian conifers, we conducted 13CO2 and 13C-glucose labelling studies with Norway spruce (Picea abies L.) and Scots pine (Pinus sylvestris L.). The results from the labelling experiments were further compared to diurnal modulations measured for the emission fluxes of the respective terpenoids, as well as to their release from reservoirs in needles and bark tissue.

The comparison allowed the following comprehensive statements for the investigated conifers. Consistent to other studies, we found that constitutive monoterpene emissions mainly originate from storage pools but with compound-specific fractions of de novo emissions. In contrast, stress-induced monoterpene and sesquiterpene emissions are entirely of de novo nature. We also found at least three different carbon sources for monoterpene and sesquiterpene biosynthesis. These sources differ with respect to the timescale after which the recently assimilated carbon reappears in the emitted terpenoids. Carbon directly obtained from assimilated has a short turnover time of few hours, while carbon from other alternative carbon sources has intermediate turnover times of few days and even longer. Terpenoid biosynthesis is not restricted to the presence of light and the carbon for terpenoid biosynthesis can be delivered from the alternative carbon sources. In particular for sesquiterpenes, there can be substantial de novo emissions in darkness reaching up to around 60 % of the daytime emissions. The use of the alternative carbon sources for sesquiterpene synthesis is probably linked to the mevalonic acid (MVA) pathway. The higher the contribution of the MVA pathway to terpenoid synthesis, the higher is the nocturnal de novo emission.

In general, the emission mechanisms of monoterpene and sesquiterpene are more complex than assumed so far. Besides pools for terpenoids themselves, there are also pools for terpenoids precursors. Terpenoid synthesis from alternative carbon sources leads to nighttime emissions and hence the amplitude of diurnal modulations of terpenoid emissions may be determined by an overlap of three mechanisms involved: emissions from storage pools, emissions in parallel to CO2 uptake and emissions from alternative carbon sources.

Cheng Wu et al.
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Interactive discussion
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Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Cheng Wu et al.
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Short summary
Biogenic volatile organic compounds are important for atmospheric chemistry. We showed by 13CO2 labelling experiments that biosynthesis is not restricted to the presence of light. In particular sesquiterpenes exhibit substantial de novo emissions in darkness with the carbon being delivered from alternative carbon sources. Our findings are of importance for future emissions under conditions of climate change as the response of de novo emissions to stresses differs from that of pool emissions.
Biogenic volatile organic compounds are important for atmospheric chemistry. We showed by 13CO2...
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