Methane emission induced by short-chain organic acids in lowland soil

Abstract

Methane (CH 4 ) is the second major greenhouse gas after CO 2 , exerting a significant influence on the climate and the chemistry of the atmosphere. In lowland soil, acetate and H 2 /CO 2 are the most important precursors of CH 4 and formed from organic matter fermentation in an anaerobic environment, giving rise to short-chain organic acids (ethanoic, propanoic, and butanoic), depending on the type of crop residue and the soil management system. Ethanoic acid can be directly converted to CH 4 by methanogenic microorganisms, but propanoic and butanoic acids must be converted to acetate before being converted to CH 4 . This study aimed to quantify, in isolation, the dynamics and CH 4 emission potential of the three short-chain organic acids found in flooded lowland soils with rice crops. The study was carried out in a controlled environment using four standard carbon doses (0, 90, 180, and 270 mg kg -1 ) of ethanoic, propanoic, and butanoic acids. The dynamics and the potential emission of CH 4 from soil were investigated when the acids were applied to flooded soil previously incubated for 20 days. The CH 4 emission dynamics were altered with the application of the three short-chain organic acids to the soil, even using an equal amount of carbon. The faster and more intense emission was achieved with the ethanoic acid application in relation to the other two acids application, while butanoic acid presents slower, delayed, and prolonged dynamics of CH 4 emission. Propanoic acid resulted in the lowest CH 4 emission due to its own stoichiometry and the temperature condition in which the experiment was conducted, which were unfavorable to the hydrogenotrophic bacteria. The addition of short-chain organic acids promoted a priming effect in the soil with conversion values of C to CH 4 above the calculated theoretical values.