Humic fractions from Amazon soils: Lifetime study and humification process by fluorescence spectroscopy

International audienceThe Amazon forest is an important and primordial ecosystem, as it controls the dynamics of soil organic matter (SOM) in addition to being considered one of the most important carbon reservoirs in the world. Based on that, this study evaluated the molecular properties of humic (HA) and fulvic (FA) acid from Amazon soil, with and without Cu(II) ions, by Time Resolved Laser Fluorescence Spectroscopy (TRLFS) and Fluorescence Spectroscopy (FS). Fluorescence excitation-emission matrix (EEM) was obtained by FS, and EEM spectra were treatment by canonical polyadic/parallel factor analysis (EEM-CP/PARAFAC). The results showed that the humification index (A 465nm) determined by FS is directly dependent on fluorophores CII/CI ratio in these soils with depth (r = 0.89), especially for HA samples, in which demonstrated that the CII consist more complex and humified structure of the SOM. The decay of the lifetime showed the presence of static quenching in the humic fractions. From the decay life data provided by TRLFS and the different correlations with carbon content and A 465nm , it can be deduced that fluorescence suppression modifies the molecular properties of the humic fractions with the addition of Cu(II) ions, such as altering the mobility and availability of the metal in the complexation reactions in these Amazonian Spodosols, mainly for fulvic fraction