Gas phase measurements of pyruvic acid and its volatile metabolites

Pyruvic acid, central to leaf carbon metabolism, is a precursor of many volatile organic compounds (VOCs) that impact air quality and climate. Although the pathways involved in the production of isoprenoids are well-known, those of several oxygenated VOCs remain uncertain. We present concentration and flux measurements of pyruvic acid and other VOCs within the tropical rainforest (TRF) biome at Biosphere 2. Pyruvic acid concentrations varied diurnally with midday maxima up to 15 ppbv, perhaps due to enhanced production rates and suppression of mitochondrial respiration in the light. Branch fluxes and ambient concentrations of pyruvic acid correlated with those of acetone, acetaldehyde, ethanol, acetic acid, isoprene, monoterpenes, and sesquiterpenes. While pyruvic acid is a known substrate for isoprenoid synthesis, this correlation suggests that the oxygenated VOCs may also derive from pyruvic acid, an idea supported by leaf feeding experiments with sodium pyruvate which resulted in large enhancements in emissions of both isoprenoids and oxygenated VOCs. While feeding with sodium pyruvate-2-¹³C resulted in large emissions of both ¹³C-labeled isoprenoids and oxygenated VOCs, feeding with sodium pyruvate-1^-l3C resulted in only relabeled isoprenoids. This suggests that acetaldehyde, ethanol, and acetic acid are produced from pyruvic acid via the pyruvate dehydrogenase (PDH) bypass system (in which the 1-C carbon of pyruvic acid is lost as CO₂) and that acetone is also derived from the decarboxylation of pyruvic acid.