Biogenic Volatile Organic Compound and Respiratory CO2 Emissions after 13C-Labeling: Online Tracing of C Translocation Dynamics in Poplar Plants

Abstract

BackgroundGlobally plants are the primary sink of atmospheric CO2, but are also the major contributor of a large spectrum of atmospheric reactive hydrocarbons such as terpenes (e.g. isoprene) and other biogenic volatile organic compounds (BVOC). The prediction of plant carbon (C) uptake and atmospheric oxidation capacity are crucial to define the trajectory and consequences of global environmental changes. To achieve this, the biosynthesis of BVOC and the dynamics of C allocation and translocation in both plants and ecosystems are important.MethodologyWe combined tunable diode laser absorption spectrometry (TDLAS) and proton transfer reaction mass spectrometry (PTR-MS) for studying isoprene biosynthesis and following C fluxes within grey poplar (Populus x canescens) saplings. This was achieved by feeding either 13CO2 to leaves or 13C-glucose to shoots via xylem uptake. The translocation of 13CO2 from the source to other plant parts could be traced by 13C-labeled isoprene and respiratory 13CO2 emission.Principal FindingIn intact plants, assimilated 13CO2 was rapidly translocated via the phloem to the roots within 1 hour, with an average phloem transport velocity of 20.3±2.5 cm h−1. 13C label was stored in the roots and partially reallocated to the plants' apical part one day after labeling, particularly in the absence of photosynthesis. The daily C loss as BVOC ranged between 1.6% in mature leaves and 7.0% in young leaves. Non-isoprene BVOC accounted under light conditions for half of the BVOC C loss in young leaves and one-third in mature leaves. The C loss as isoprene originated mainly (76–78%) from recently fixed CO2, to a minor extent from xylem-transported sugars (7–11%) and from photosynthetic intermediates with slower turnover rates (8–11%).ConclusionWe quantified the plants' C loss as respiratory CO2 and BVOC emissions, allowing in tandem with metabolic analysis to deepen our understanding of ecosystem C flux.

Deoxyxylulose 5-Phosphate Synthase Controls Flux through the Methylerythritol 4-Phosphate Pathway in Arabidopsis

“…This indicated that ambient CO 2 recently fixed through photosynthesis was not the only source of carbon entering the MEP pathway. The unlabeled fraction may originate from imported PEP (itself derived from previously fixed carbon sources such as transported sugars in the xylem [Kreuzwieser et al, 2002] and remobilized starch [Schnitzler et al, 2004]), and refixation of CO 2 evolved from mitochondrial and photorespiration (Ghirardo et al, 2011;Szecowka et al, 2013). The maximum proportion of labeling varied insignificantly under different levels of DXS activity, from which we conclude that the carbon source supplying the MEP pathway does not change when DXS activity is altered.…”

Isoprene in poplar emissions: effects on new particle formation and OH concentrations

“…Low molecular weight, C 1 and C 2 -compounds, such as methanol, ethanol, formaldehyde, and acetaldehyde can be synthesized via other biosynthetic routes (Kreuzwieser et al, 1999). Current estimates assume that between 2-5 % of the photosynthetically assimilated carbon are released in the form of VOCs (Kesselmeier et al, 2002;Ghirardo et al, 2011) and in general stress increases VOC emissions. Despite all information on VOCs biosynthesis and biological and ecological functions (for reviews see Holopainen and Gershenzon, 2010;Loreto and Schnitzler, 2010) there is limited information about the role of these VOCs in secondary organic aerosol formation.…”

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

“…The contributions of multiple carbon sources to isoprene biosynthesis are well discussed in previous studies (Kreuzwieser et al, 2002;Schnitzler et al, 2004;Ghirardo et al, 2011): carbon taken from atmospheric CO 2 , xylem transported glucose and other leaf internal carbon pools, e.g. starch, can contribute together to isoprene biosynthesis and cause the uncomplete labelling of the emitted molecules.…”

“…On 25 the day before the 13 C-glucose experiment, small branches of the individual plants were carefully cut and immediately transferred into a small glass chamber of 3 L volume. They were re-cut under water and initially fed with 10mM glucose solution (Kreuzwieser et al, 2002;Ghirardo et al, 2011) containing the natural abundance of 13 C. The small chamber was placed in the same walk-in climate chamber as the tested plants and equipped with an extra discharge lamp causing a light intensity of approximately 600 μmol m -2 s -1 , similar as for the living plants. Between 1.5-2 L min -1 of the air containing 350 30 ppm CO 2 with the natural 13 C abundance was pumped through the small chamber.…”

“…Experiments with feeding 13 C-enriched carbon sources such as 13 CO 2 and 13 C-glucose allow studying the contributions of different carbon sources to the terpenoid synthesis (Karl et al, 2002;Kreuzwieser et al, 2002;Loreto et al, 2004;Schnitzler et al, 2004;Ghirardo et al, 2011). Besides atmospheric CO 2 , alternative carbon sources contribute simultaneously to isoprene and monoterpene biosynthesis and their contribution become especially important when photosynthesis is limited 25 (Brilli et al, 2007).…”