Study of the acid-base properties of leaf litter extracts

Abstract

The acid-base properties of four leaf litter extracts, LLE (eucalyptus, fern, oak and chestnut coverture), were characterized by synchronous fluorescence (SyF) spectroscopy and compared with those of two fulvic acids (FA) extracted from two different horizons (0–5 and 5–15 cm) of an oak forest soil. The characterization was based on the variation with the pH of the properties of the fluorescent structures present in the samples, which function as probes and provide a macroscopic image of their acid-base properties. These sets of SyF spectra collected as a function of the pH show fingerprinting potential. They were treated by a self-modeling curve resolution procedure, evolving factor analysis with a gradient concentration window (EFA-GCW), to reduce the raw spectral data to the number of components, their spectra, and SyF intensity profiles (pH distribution diagrams). Four acid-base systems were detected for all samples of LLE and FA with pKas ranging from 2.5 to 10.0 (pKas about 3, 5, 7 and 9, except for the fern LLE sample which showed pKas about 5, 7, 9 and 10). A similarity analysis of the spectra of the components, performed by cluster analysis, showed that the most acidic fluorescent structures of the LLE are not similar to those of the soil FA, but the less acidic are.