This study examined the chemical and structural properties of humic substances and microbiological activity inorder to verify differences in carbon dynamics along soil profiles in two Vertisols (Typic Haploxerert and XericEpiaquert) and two Alfisols (Mollic Haploxeralf and Ultic Haploxeralf) developed under Mediterranean climatein Italy. Humification parameters, thermal methods, including differential scanning calorimetry (DSC) andthermogravimetry (TG), together with Fourier transform infrared (FT-IR) and fluorescence spectroscopieswere used to characterize humic acids (HA). Microbiological activity of soils was assessed by basal respiration,metabolic quotient (qCO2) and Cmic:Corg ratio. FT-IR spectra and thermal analysis DSC/TG of HA extracted fromthe upper horizons showed a higher aliphatic character, whereas HA extracted from the lower horizons had ahigher content of aromatic structures and polysaccharides. Moreover, the fluorescence index of the HA (HIXflu)showed a higher degree of aromatic polycondensation in the subsoils. The Cmic:Corg ratio was negativelycorrelated with the HIXflu of HA (Pb0.05), while qCO2 was positively correlated with the labile components ofHA (Exo1/(Exo2+Exo3)) (Pb0.05). These results suggest reduced C availability in deep horizons where HAstructures resulted in complex and thermally more stable molecules. Following discriminant function analysisall the chemical and microbiological properties with the exception of labile thermal fraction of HA and soil pHlargely varied between B and the upper horizons. In deep horizons of both Vertisols and Alfisols the microbialbiomass was nutritionally stressed with a low efficiency in C turnover. No correlation was found betweenspecific soil processes, such as argilliturbation or clay illuviation and humic substances properties or soilmicrobial biomass and activity.
|Numero di pagine||9|
|Stato di pubblicazione||Published - 2010|
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