Forecasting soil organic carbon sequestration based on the increased Complexity of pyrolytic methoxyphenols

Comunicación oral presenta en el la XVI Reunión Científica de la Sociedad Española de Cromatografía y Técnicas Afines (SECyTA2016) OJ‐ENV‐5Eds: González-Pérez, José Antonio.-- Almendros Martín, Gonzalo.-- González-Vila, Francisco Javier.-- Rosa Arranz, José M. de laDespite considerable progress during the past decades in the knowledge of the factors presumptively involved in soil carbon sequestration, additional research is required to establish the variability of these factors in space and time. Such knowledge is crucial to progress in the development of the scientific bases of Earth’s biogeochemical cycle and global change. For this reason, we intend to find out useful proxies from soil organic matter characteristics or other soil properties which could play a role in soil carbon sequestration. For this study, we collected topsoil samples from up to 35 Spanish soils with different carbon content, geological substrate, vegetation and use. The study of soil organic matter composition was carried out by pyrolysis‐gas chromatography‐mass spectrometry (Py‐GC/MS) of whole soil samples. This technique displays a large potential to identify and asses relative proportions of the different organic compounds present in the soil. The technique does not require any pretreatment or previous sample extraction. Methoxyphenols are typical pyrolysis products from soil organic matter, with an origin from plant biomacromolecules mainly lignin. Major methoxyphenols in soils correspond to 4‐H‐, methyl‐, ethyl‐, vinyl‐ and propenyl derivatives of guayacol and syringol. We apply several multivariate data treatments aiming to explain the total amount of soil organic matter in the different soils (dependent variable) as a function of the composition of its pyrolysis products. In particular and in order to express the complexity of the molecular composition of the different pyrolysis compounds, we applied the Shannon‐Wiener biodiversity index, classically used to characterize species diversity in a community. In this research, the ‘species’ selected are the different methoxyphenols. Partial least squares regression exclusively using the total abundances of methoxyphenols yielded highly significant (P< 0.01) forecasting models which explain the concentration of organic C sequestered I the different soils. This leads to the suggestion that significant correlation exists between effective soil C storage and the more or less advanced stages of transformation of the organic matter. In fact, when the Shannon biodiversity index was calculated for the 12 major methoxyphenols, a significant correlation was found with the total organic C stored in the soils. This finding suggests that C sequestration behave as a soil emergent property which is reflected by the sources, complexity and interactions of the soil organic matter constituents at a molecular level, which would result into the accumulation of recalcitrant C‐forms with increasingly chaotic structure, i.e., not readily recognized by soil enzymes.N