Article pubs.acs.org/est
Cite This: Environ. Sci. Technol. 2018, 52, 13811−13823
New Perspectives on CO2, Temperature, and Light Effects on BVOC Emissions Using Online Measurements by PTR-MS and Cavity RingDown Spectroscopy Jianbei Huang,*,† Henrik Hartmann,† Heidi Hellén,‡ Armin Wisthaler,§ Erica Perreca,∥ Alexander Weinhold,⊥ Alexander Rücker,† Nicole M. van Dam,⊥,# Jonathan Gershenzon,∥ Susan Trumbore,† and Thomas Behrendt*,† Downloaded via UNITED ARAB EMIRATES UNIV on January 14, 2019 at 10:23:32 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
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Max-Planck-Institute for Biogeochemistry, Jena, Germany Finnish Meteorological Institute, Helsinki, Finland § Department of Chemistry, University of Oslo, Oslo, Norway ∥ Max Planck Institute for Chemical Ecology, Jena, Germany ⊥ German Centre for Integrative Biodiversity Research, Leipzig, Germany # Institute of Ecology, Friedrich Schiller University, Jena, Germany ‡
S Supporting Information *
ABSTRACT: Volatile organic compounds (VOC) play important roles in atmospheric chemistry, plant ecology, and physiology, and biogenic VOC (BVOC) emitted by plants is the largest VOC source. Our knowledge about how environmental drivers (e.g., carbon, light, and temperature) may regulate BVOC emissions is limited because they are often not controlled. We combined a greenhouse facility to manipulate atmospheric CO2 ([CO2]) with proton-transferreaction mass spectrometry (PTR-MS) and cavity ring-down spectroscopy to investigate the regulation of BVOC in Norway spruce. Our results indicate a direct relationship between [CO2] and methanol and acetone emissions, and their temperature and light dependencies, possibly related to substrate availability. The composition of monoterpenes stored in needles remained constant, but emissions of mono-(linalool) and sesquiterpenes (β-farnesene) increased at lower [CO2], with the effects being most pronounced at the highest air temperature. Pulse-labeling suggested an immediate incorporation of recently assimilated carbon into acetone, mono- and sesquiterpene emissions even under 50 ppm [CO2]. Our results provide new perspectives on CO2, temperature and light effects on BVOC emissions, in particular how they depend on stored pools and recent photosynthetic products. Future studies using smaller but more seedlings may allow sufficient replication to examine the physiological mechanisms behind the BVOC responses.
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INTRODUCTION Volatile organic compounds (VOC) play important roles in atmospheric chemistry and climate by altering the oxidative capacity of the atmosphere,1−3 ozone production in the presence of NOx (NO+NO2),4 and the formation of secondary organic aerosols.5 Biogenic VOC (BVOC) is the largest VOC source, representing up to ∼90% of total emissions.6 However, our limited understanding of the function and regulation of BVOC results in large uncertainties in estimating and predicting BVOC emissions.7,8 Temperature and light are commonly viewed as key environmental factors controlling BVOC emissions.6 A rise in the mean global temperature of ∼2−3 °C is expected to increase total BVOC emissions by 30−45%.9 In global vegetation models such as ORCHIDEE,10 light intensity is the main driver of the emissions, accounting for 80% and 60% © 2018 American Chemical Society
of methanol and monoterpenes, repectively. However, changing atmospheric [CO2] may also affect BVOC emissions, as increasing [CO2] from low (∼190 ppm) to high (∼600 ppm) has been shown to suppress isoprene emissions.11,12 While such mechanisms that give rise to isoprene emissions have been implemented in models,13,14 the information on the physiological regulation of other BVOC emissions, for example, mono- and sesquiterpenes as well as oxygenated BVOC, is still limited. Mono- and sesquiterpenes serve important biological and ecological functions, such as repelling herbivores and attracting Received: Revised: Accepted: Published: 13811
March 16, 2018 September 21, 2018 October 18, 2018 October 18, 2018 DOI: 10.1021/acs.est.8b01435 Environ. Sci. Technol. 2018, 52, 13811−13823
Article
Environmental Science & Technology
Figure 1. Schematic view of [CO2] manipulation system in the greenhouse. MFC, mass flow controller; PTR-MS, proton-transfer-reaction mass spectrometry.
their predators,15 or scavenging harmful reactive oxygen species (ROS) in plants.16 Hence, their emissions are often induced by biotic and abiotic stresses such as herbivory, intense light and high temperature.17,18 It remains unclear whether emitted monoterpenes are released from stored pools or synthesized de novo. Data on the third group of isoprenoids, sesquiterpenes, are still sparse because these compounds degrade rapidly due to their high chemical reactivity with radicals (e.g., hydroxyl radical, OH) and ozone (O3).19,20 Plants also emit large quantities of oxygenated VOC (e.g., methanol and acetone) into the atmosphere.10,21 Methanol is thought to be a byproduct of pectin demethylation during cell wall extension,22,23 and is therefore often used as an indicator of growth.24 Saccharides including glucose and sucrose are required for pectin synthesis,25 which may play an important role in regulating methanol emissions.26 The metabolic pathways involved in the synthesis of acetone are not yet fully understood, but it is likely that acetone is produced via pyruvate metabolism.27 Field observations demonstrate that emissions of methanol and acetone are temperature- and lightdependent,28−30 but their dependence on carbon has received less attention. In particular, quantification of interactions between temperature, light and [CO2] on emissions and dynamics of these fluxes are still not well understood. To fill this gap, we constructed a greenhouse facility specifically designed to induce contrasting carbon availability, spanning very low to ambient [CO2] concentrations (400, 180, and 50 ppm). We combined proton transfer reaction mass spectrometry (PTR-MS) with gas chromatography−mass spectrometry (GC−MS) to investigate emissions of terpenoids and oxygenated BVOC from whole-canopies (including stem, branches and needles) of 8-year-old Norway spruce (Picea abies). We also monitored CO2 and water vapor gas exchange, air temperature, and photosynthetically active radiation (PAR) to investigate their relationships to BVOC emissions. Concentrations of metabolites including soluble sugars and monoterpenes in tissues were measured to investigate the role of substrate availability in BVOC emissions. Isotope labeling
allows partitioning the contribution of stored pools and recent photosynthetic products to BVOC emissions. Such an approach has been successfully applied for determining carbon source for isoprene emissions under different [CO2],31−33 and monoterpene emissions following herbivory.34 Hence, we also employed 13CO2 pulse-labeling and traced labeled C into emissions of acetone, mono-, and sesquiterpenes in all [CO2] treatments.
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MATERIALS AND METHODS Plant Material. We conducted two experiments, one in 2016 (experiment I) one and 2017 (experiment II) using two genotypes of 8-year-old Norway Spruce saplings (S21K0420117 and S21K04200232 from Sweden). Prior to each experiment, trees were grown outdoors in pots filled with sand and a slow-releasing fertilizer (Osmocote Start, Everris International B.V., Netherlands). All saplings were pruned in July 2015 to make them fit into the growth chambers and were watered regularly before the start of the experiment. Growth Chambers. Four cylindrical chambers (height = 70 cm, diameter = 70 cm, volume = 270 L) covered with fluorinated ethylene propylene (FEP) foil were built to enclose the whole aboveground portion of the spruce saplings (Supporting Information Figure S1). Previous studies found that FEP foil transmits about 95% of photosynthetically active radiation (PAR, 400−700 nm) and about 90% for wavelengths
