Soil carbon storage predicted from the diversity of pyrolytic alkanes

Biogeochemical factors responsible of the highly variable content of soil organic matter (SOM) in the different types of soils are poorly known. In particular, the role of organo-mineral interactions has frequently been considered, but less attention has been paid to the molecular composition of the SOM. The aim of this work was to contribute to a better qualitative and quantitative assessment of the soil organic C (SOC) accumulation, using chemometric approaches that do not require the absolute knowledge of the structure and functioning of the whole system under study. For this reason, we monitored the n- alkanes released by analytical pyrolysis from 35 widely different Mediterranean soils. The H′ Shannon diversity index was calculated to evaluate the origin and transformations of the alkane homologous series (C 9 –C 31 ). A series of multivariate data treatments succeeded in showing significant relationship between the diversity of alkanes and the SOC concentration, and additional indicators of SOM quality were also used. All statistical analyses pointed out the significant correlation ( P < 0.01) between the H′ diversity of the pyrolytic alkanes and the amount of SOC. In particular, a significant relationship between SOC levels and the percentage of long-chain alkanes was found, whereas the percentage of short-chain alkanes was correlated with specific descriptors of SOM quality. Finally, the partial least squares (PLS) predicted the SOC content from the alkane patterns.