Tracing ecosystem scale interactions of volatile organic compound (VOC) and CO2 emissions by position-specific and whole ecosystem isotope labelling

Ecosystem processes present a complex interplay between different components, such as vegetation, soil, and the rhizosphere. All these different components can emit (or even uptake) a plethora of volatile organic compound (BVOC) with highly dynamic response to environmental changes. However, processes controlling carbon allocation into primary and secondary metabolism such as VOC synthesis or respiratory CO₂ emission remain unclear. De novo synthesis of BVOC depends on the availability of carbon, as well as energy provided by primary metabolism. Thus, carbon allocation may compete between primary and secondary metabolism, which are linked via a number of interfaces including the central metabolite pyruvate. It is the main substrate fulling respiration, but also a substrate for a large array of secondary pathways leading to the biosynthesis of many volatile organic compounds, such as volatile isoprenoids, oxygenated VOCs. Within the European Research Council (ERC) Project VOCO we developed a novel technological basis to couple CO₂ fluxes with VOC emissions based on simultaneous real-time measurements of stable carbon isotope composition of branch, root, and soil respired CO₂ and VOC fluxes (Fasbender et al. 2018). Position specific ¹³C-labeled pyruvate feeding experiments are used to trace partitioning within the metabolic branching points into VOCs versus CO₂ emissions, bridging scales from sub-molecular to whole-plant and ecosystem processes. Positional 13C-labelling will trace real-time sub-molecular carbon investment into VOCs and CO₂, enabling mechanistic descriptions of the underlying biochemical pathways coupling anabolic and catabolic processes.

To trace ecosystem scale interactions, we implemented a whole-ecosystem labelling approach in the world’s largest controlled growth facility: the Biosphere 2 Tropical Rainforest. In the Biosphere 2 Water, Atmosphere, and Life Dynamics (B2-WALD) experiment, we applied an ecosystem scale drought and tracing carbon allocation and dynamics of VOC, CO₂ and H₂O fluxes from leaf, root, soil and atmospheric scales. The overarching goal of B2-WALD is to track, biological mechanisms controlling the fate of CO₂, VOC and water cycling in an ecosystem under change in an interdisciplinary approach. This comprehensive data set will be used for carbon and water partitioning from the metabolic to ecosystem scale

Fasbender L., et al. (2018). A novel approach combining PTR-TOF-MS, ¹³CO₂ laser spectroscopy and ¹³C-metabolite labelling to trace real-time carbon allocation into BVOCs and respiratory CO₂. PLOS One,13: e0204398