Valeria D’Orazio

Chemical and spectroscopic characteristics of humic acids and dissolved organic matter along two Alfisol profiles.

The aim of this study was to elucidate the heterogeneous structural and functional composition of humic acids (HAs) and dissolved organic matter (DOM) isolated from two Alfisol profiles with different soil texture, in order to develop a better understanding of the organic matter dynamics. Soil samples were collected at different depths from three (Ap, 2AB and 2Bt) and eight (A1, A2, A3, E1, E2, 2Bt1, 2Bt2 and 2Bt3) soil horizons of two Alfisols located in the south (PR1) and north (PR2) of Italy, with a clay texture and a silt loam to loam ones, respectively. Chemical and spectroscopic methods were used to characterize the HAs and the DOM isolated from different soil horizons, including Ultraviolet-Visible (UV-Vis), Fourier Transform Infrared (FTIR), and Fluorescence spectroscopies. The HAs and the DOM isolated from the two Alfisols apparently showed significant differences in their compositional, structural and functional characteristics. In particular, the HAs isolated from the PR1 featured a higher degree of humification and molecular complexity with respect to those isolated from the PR2. On the contrary, the DOM samples isolated from the PR2 showed a more marked aromatic character and polycondensation degree. Both the HAs and the DOM obtained from the PR1 presented a greater qualitative homogeneity with respect to those obtained from the PR2. These results could be reasonably ascribed to the different texture and horizons of the two Alfisols, and to a greater pedogenesis occurred in the PR1.

Properties of humic acids in Mediterranean forest soils (Southern Italy): influence of different plant covering

The chemical and spectroscopic properties of humic acids (HAs) isolated from four litters and their corresponding underlying soils at three depths in a protected forest area in Southern Italy were investigated as a function of four different plant coverings: Quercus ilex L., mixed Carpinus betulus L. and C. orientalis Mill., Pinus halepensis L., and mixed Quercus trojana Webb. and Q. ilex L.. The forested site is a part of a calcareous plateau, characterized by homogeneous soils classified as Eutric Cambisols associated with Calcic Luvisols. The changes in the composition of HAs with soil depth have been evaluated on the basis of chemical (elemental and COOH groups) and spectroscopic analyses (E4/E6 ratio and FT IR spectra), and lignin-derived CuO oxidation products. A different distribution of the main elements was found in the various HAs which is apparently related to the type of humic acid-precursor biomolecules in the parent litters. The HAs isolated from soils under Q. ilex and mixed Carpinus species showed a slight increase in the C/H ratio and COOH content downward the soil profile, suggesting increasing aromatic polycondensation and humification degree with depth. On the contrary, no trend was observed for HAs from soils under Pinus halepensis L. and mixed Quercus species, indicating a partial incorporation of residues deriving from litter degradation into these HAs. Further, the content of lignin-derived phenols was higher in Pinushalepensis L. and mixed Quercus species layers, with the same trend measured for the corresponding HAs, thus confirming a lignin contribution related to the lignin type of plant covering.

Highly anomalous accumulation rates of C and N recorded by a relic, free-floating peatland in Central Italy

Floating islands mysteriously moving around on lakes were described by several Latin authors almost two millennia ago. These fascinating ecosystems, known as free-floating mires, have been extensively investigated from ecological, hydrological and management points of view, but there have been no detailed studies of their rates of accumulation of organic matter (OM), organic carbon (OC) and total nitrogen (TN). We have collected a peat core 4 m long from the free-floating island of Posta Fibreno, a relic mire in Central Italy. This is the thickest accumulation of peat ever found in a free-floating mire, yet it has formed during the past seven centuries and represents the greatest accumulation rates, at both decadal and centennial timescale, of OM (0.63 vs. 0.37 kg/m2/yr), OC (0.28 vs. 0.18 kg/m2/yr) and TN (3.7 vs. 6.1 g/m2/yr) ever reported for coeval peatlands. The anomalously high accretion rates, obtained using 14C age dating, were confirmed using 210Pb and 137Cs: these show that the top 2 m of Sphagnum-peat has accumulated in only ~100 years. As an environmental archive, Posta Fibreno offers a temporal resolution which is 10x greater than any terrestrial peat bog, and promises to provide new insight into environmental changes occurring during the Anthropocene.

Forest soil organic carbon dynamics as affected by plant species and their corresponding litters: a fluorescence spectroscopy approach

Background and aimsThe effect of forest cover distribution and plant litter input on soil organic carbon were analyzed to better understand the dynamics of carbon cycling across ecosystems on the “Natural Oriented Reserve Bosco delle Pianelle”. Fluorescence spectroscopy represents a very useful tool to characterize soil organic matter properties, since it allows to directly monitor the molecular status of a fluorophore depending on its chemical environment, as well as on its structure, substituents of the aromatic moieties, and molecular weight. Here, fluorescence analysis was performed on humic acids isolated from four litters (HALs) and their underlying soils (HAs) at three depths.MethodsAll samples were collected from a protected forest area, Southern Italy, under different plant covering: Quercus ilex L. (Q), mixed Carpinus betulus L. and Carpinus orientalis Mill. (CC), Pinus halepensis L. (P), and mixed Quercus trojana Webb. and Quercus ilex L. (QQ).ResultsData obtained showed a fast decomposition process for P and QQ litters, with HAs in the underlying soils characterized by the presence of simple, highly fluorescent structural components also in the deepest layers. On the contrary, a slow decomposition process was observed for Q and CC litters, whose underlying soil HAs were characterized by an increasing aromatic polycondensation and humification degree from the surface to the deepest layers, as supported by low values of fluorescence intensity and high wavelength maxima.ConclusionsResults obtained indicate that P and QQ species promote C accumulation and stock in the underlying soils, thanks to a greater decomposition of their litter, and fluorescence spectroscopy is a very simple and suitable method to evaluate the influence of three species distribution on soil organic carbon pools.

Interactions between rotenone and humic acids by means of FT-IR and fluorescence spectroscopies

The aim of this work was to ascertain, on a comparative basis, the compositional, structural and functional differences occurring between three humic acids (HAs), HA S1 (isolated from a Mediterranean brown soil), HA S2 (isolated from a Bavarian brown soil), and HA SR (a Suwannee River standard aquatic HA, purchased from IHSS), and to investigate the influence of their intrinsic properties on the types of binding mechanisms toward the pesticide rotenone. Original HAs and their corresponding HA–rotenone products, obtained by two different interaction protocols, were analyzed for elemental and functional group composition, and spectroscopic techniques, such as Fourier-transform infrared (FT IR) with Fourier self-deconvolution (FSD) and fluorescence both in the single-scan and in three-dimensional modes. The HA S1 sample appeared to be characterized by a greater aromaticity degree and lower polarity with respect to the HA S2, featured by a mixed aromatic/aliphatic character, whereas mainly aliphatic and acidic resulted the HA SR. The data obtained suggested that the low water-soluble, non-polar pesticide rotenone resulted preferentially adsorbed onto HAs by hydrophobic interaction, that was the prevailing mechanism in the order HA S1 > HA S2 >>> HA SR, whereas hydrogen bonds resulted predominant in the opposite order.

Fluorescence properties of humic acid interaction products with s-triazine and bipyridilium herbicides and their Cu complexes: a multivariate approach

PurposeExcitation–emission matrices spectroscopy (EEMS) of soil humic acids (HAs) contains large amount of information on their properties, as well as on the dynamics related to their intra- and inter-molecular interactions. The objective of this research was (i) to show that EEMS represents a useful tool to investigate the molecular and mechanistic aspects of HA adsorbing capacity towards atrazine (A) and paraquat (P) with or without Cu2+ ions and (ii) to evaluate if additional information on these mechanisms can be obtained by combining EEMS with principal component analysis (PCA).Materials and methodsHAs have been isolated from soil samples collected in a citrus field at three locations, within the plant rows (HAa); between the rows (HAb) and in a adjacent, control soil (HAc). Interaction products were obtained between each HA and A and P, with or without Cu ions. Elemental analysis and Fourier-transorm Infrared Spectroscopy were applied to support fluorescence data. Fluorescence spectra were recorded on aqueous solutions, and fluorescence intensity (FI) values were normalized using a quinine sulphate standard. PCA analysis was performed using the software STATGRAPHICS Centurion XV.I.Results and discussionThe EEM spectra of the three unreacted HAs are characterized by the presence of two fluorophores α and β, in the region of longer wavelengths pairs (EEWP). The EEM spectra of the HA-A interaction products are featured by the same two fluorophores, with FI values decreased of about 50%, whereas those of the HA-P interaction products show a unique peak, γ, at intermediate EEWP. Finally, the EEM spectra of HA-A-Cu2+ show, with respect to HA-A samples, a blue shift of the α peak with an additional decrease of FI values (about 60%) and the disappearance of the peaks β, whereas those of HA-P-Cu2+ feature, in comparison with those of HA-P, a small red-shift of the peak γ. PCA data suggest that Cu ions do not affect the interaction mechanism between HA and P, whereas it appears to exercise a strong influence on interaction between HA and A.ConclusionsThe results obtained indicate that EEMS allows direct measurements of the adsorbing capacity of HA towards atrazine and paraquat. Additional information obtained by PCA analysis show that Cu ions behave like a good antagonist in preventing the formation of ionic bonds between HA and atrazine, whereas Cu is not able to affect the prevalent mechanism of HA interaction with paraquat, which is a charge-transfer bond.

Trace Elements and Food Safety

Food is our energy source and limited access to food impacts health in multiple ways. Typically, food is thought to have a positive impact on health by providing energy and essential nutrients to living beings. Despite this, often it is so detrimental to health and several foodborne diseases clearly indicate that food safety not only involves availability and access to food, but that the food must be wholesome as well. The threat to food security is depending on urbanization, income disparity, overpopulation, ecosystem degradation, animal health, etc.