Molecular composition and possible transformations of labile soil organic matter fractions in Mediterranean arable soils: Relevance and implications.

With the increased global interest in sequestering carbon in soil, it is necessary to understand the composition of different pools of soil organic matter (SOM) that cycle over suitably short timeframes. To explore in detail the chemical composition of agroecologically relevant yet distinct fractions of SOM, the light fraction of SOM (LFOM), the 53-µm particulate organic matter (POM), and the mobile humic acid (MHA) fractions were sequentially extracted from agricultural soils and characterized using both 13C cross polarization magic angle spinning nuclear magnetic resonance (CPMAS NMR) spectroscopy and also Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The NMR results showed a decrease in the O-alkyl C region assigned to carbohydrates (51-110 ppm) and an increase in the aromatic region (111-161 ppm) proceeding from the LFOM to the POM and then to the MHA fraction. Similarly, based on the thousands of molecular formulae assigned to the peaks detected by FT-ICR-MS, condensed hydrocarbons were dominant only in the MHA, while aliphatic formulae were abundant in the POM and LFOM fractions. The molecular formulae of the LFOM and POM were mainly grouped in the high H/C lipid-like and aliphatic space, whereas a portion of the MHA compounds showed an extremely high (17-33, average of 25) double bond equivalent (DBE) values, corresponding to low H/C values of 0.3-0.6, representative of condensed hydrocarbons. The labile components appeared most pronounced in the POM (93% of formulae have H/C ≥ 1.5) similar to the LFOM (89% of formulae have H/C ≥ 1.5) but in contrast to the MHA (74% of formulae have H/C ≥ 1.5). The presence of both labile and recalcitrant components in the MHA fraction suggests that the stability and persistence of soil organic matter is influenced by a complex interaction of physical, chemical, and biological factors in soil. Understanding the composition and distribution of different SOM fractions can provide valuable insights into the processes that govern carbon cycling in soils, which can help inform strategies for sustainable land management and climate change mitigation.

Chemical Composition, Biomolecular Analysis, and Nuclear Magnetic Resonance Spectroscopic Fingerprinting of Posidonia oceanica and Ascophyllum nodosum Extracts.

A detailed analysis of the elemental and molecular composition of Posidonia oceanica (PO) and Ascophyllum nodosum (AN) is presented. In particular, an in-depth study of the molecular identification via NMR spectroscopy of aqueous and organic extracts of PO and AN was carried out, exploiting 2D COSY and pseudo-2D DOSY data to aid in the assignment of peaks in complex 1D proton NMR spectra. Many metabolites were identified, such as carbohydrates, amino acids, organic acids, fatty acids, and polyphenols, with NMR complementing the characterization of the two species by standard elemental analysis, HPLC analysis, and colorimetric testing. For PO, different parts of the live plant (roots, rhizomes, and leaves) were analysed, as well as the residues of the dead plant which typically deposit along the coasts. The combination of the various studies made it possible to recognize bioactive compounds naturally present in the two plant species and, in particular, in the PO residues, opening the door for their possible recycling and use in, for example, fertilizer. Furthermore, NMR is proven to be a powerful tool for the metabolomic study of plant species as it allows for the direct identification of specific biomarkers as well as providing a molecular fingerprint of the plant variety.

Selected Plant-Related Papers from the First Joint Meeting on Soil and Plant System Sciences (SPSS 2019)-"Natural and Human-Induced Impacts on the Critical Zone and Food Production".

The First Joint Meeting on Soil and Plant System Sciences (SPSS 2019), titled "Natural and Human-Induced Impacts on the Critical Zone and Food Production", aimed at integrating different scientific backgrounds and topics flowing into the Critical Zone, where chemical, biological, physical, and geological processes work together to support life on the Earth's surface. The SPSS 2019 meeting gathered the thoughts and findings of scientists, professionals and individuals from different countries working in different research fields. This Special Issue comprises a selection of original works on the plant-related topics presented during this international meeting.

Biochar effect on crop performance and Pb and Zn uptake of tomato (Solanum lycopersicum, L.) plants grown on heavy metals contaminated Kosovo soils.

A greenhouse pot experiment was conducted to evaluate the effect of biochar on the growth and uptake of Pb and Zn by tomato plants (Solanum lycopersicum, L.) cultivated in two highly contaminated Kosovo soils, A and B. Plants were cultivated in the biochar amended and unamended soils. As expected, the biochar addition to the two polluted soils has contributed to significantly improve the crop yields, in terms of both fresh and dry weight. Further, results indicated that the effect of biochar on metal mobility is closely related, besides its properties, to soil's native characteristics. In fact, the addition of biochar to soil B had also beneficial effects on the uptake of both metals, halving in some cases the values of the biological accumulation and transfer coefficients, while it did not show the same efficacy on soil A.

Natural Mn-todorokite as an efficient and green azo dye-degradation catalyst.

A natural Mn mineral, i.e., todorokite [(Ca,Na,K)X(Mn4+,Mn3+)6O12·3.5H2O], has been collected in the Apulia region, south of Italy, and evaluated as an oxidation catalyst for the degradation of methyl orange (MO) dye. This Mn-todorokite mineral has been firstly characterized by X-ray diffraction, wavelength-dispersive X-ray fluorescence, BET, scanning electron microscopy, attenuated total reflectance Fourier transform infrared spectroscopy, and thermogravimetry. Catalytic dye-degradation data show that this Mn-todorokite can operate under strongly oxidizing potentials (Eh > + 400 mV) vs. standard hydrogen electrode performing fast MO degradation (t1/2 < 1 min). A detailed study using electron paramagnetic resonance spectroscopy revealed that, under oxidative conditions (Eh > + 450 mV), the active Mn centers of todorokite evolve rapidly through Mn3+/Mn4+ states and this is correlated with the fast catalytic degradation of MO. These results suggest Mn-todorokite mineral as an efficient, low-cost, and green catalyst which can be used for industrial and environmental purposes.

How can the role of leachate on nitrate concentration and groundwater quality be clarified? An approach for landfills in operation (Southern Italy).

Where the unique natural water resource is groundwater, the attention and the susceptibility of local communities and authorities to groundwater quality degradation risks can be so high to determine relevant problems to waste management, especially for landfills in operation or to be realised. A multi-methodological approach was suggested with the purpose to clarify the role of landfill leakage on groundwater quality degradation. The selected study area (SSA) hosts some landfills in a narrow portion of a wide and deep coastal karstic aquifer, for these characteristics to be considered a case of high hydrogeological complexity and vulnerability. News concerning nitrate and secondly iron groundwater concentration anomalously high caused concern in the population and strong local opposition to landfills. The multi-methodological approach includes: the hydrogeological site characterization; the chemical study and the multi-isotope characterization of groundwater and leachate; the land use analysis and the estimation of nitrogen contributions deriving from fertilizers; the mineralogical study of groundwater suspended particles to define the role of natural soil substances. The hydrogeological site characterisation highlighted the local peculiarities of the aquifer. The chemical study was used to define geochemical features, groundwater and leachate characteristics and their macroscopic mixing. The environmental isotopes of hydrogen, carbon, nitrogen, and oxygen were used to investigate the groundwater origin, the most relevant geochemical reactions, the existence of groundwater-leachate mixing, and the sources of anthropogenic NO3-. The land use analysis highlighted quantity and type of used fertilizers permitting to compare these with groundwater in terms of isotopic signature. The mineralogical study demonstrated the role of suspend natural particles due the presence of terre rosse (red or residual soils) in groundwater. The approach confirmed that there are not the groundwater quality degradation effects of landfills, contributing to reassure population and institutions, simplifying the waste management.

Methylated arsenic species throughout a 4-m deep core from a free-floating peat island.

Arsenic (As) occurs in soils mostly in inorganic forms, whereas the organic forms usually occur only in trace amounts. Peatlands are waterlogged, generally anoxic, organic soils representing the first step in coal formation; the contribution of organic vs. inorganic As species in this environment has received little research attention. Here, 57 peat samples collected throughout a 4-m deep, free-floating mire were analysed for total As and for its organic species, including dimethylarsinic acid (DMA), methylarsonic acid (MA), trimethylarsine oxide (TMAO) and arsenobetaine (AB), by HPLC-ICPMS. Aqueous trifluoroacetic acid was used as extractant, resulting in an average extraction efficiency of almost 80%. Total As concentration throughout the profile ranged between 0.2 and 9.8mg/kgpeat (mean: 1.4±1.2mg/kgpeat). Organic As species (DMA+MA+TMAO+AB) accounted, on average, for 28±10% of total As (range: 6-51%), and for 37±13% of the extracted As (range: 7-64%). The relative abundance of organoarsenicals generally followed the order DMA>TMAO~MA≫AB. A positive correlation (p<0.001) was found among all organic As compounds, whereas their concentrations were negatively correlated with total sulfur content. The submerged zone (bottom 300cm) showed average and maximum concentrations of organoarsenic compounds that were almost twice those found in the top 100cm. This study shows that significant proportions of methylated As species occur even in peat samples characterized by low total As concentration (mostly <2mg/kg). Finally, this work provides the first evidence of organoarsenic species in free-floating mires, i.e., a globally distributed but scarcely investigated ecosystem.

Assessment of addition of biochar to filtering mixtures for potential water pollutant removal.

Green roofs are used increasingly to alleviate peaks of water discharge into the sewage systems in urban areas. Surface runoff from roofs contain pollutants from dry and wet deposition, and green roofs offer a possibility to reduce the amounts of pollutants in the water discharged from roofs by degradation and filtering. These pollutants would otherwise enter wastewater treatments plants and ultimately end up in sewage sludge that is spread on agricultural soils. The most common substrates used in green roofs have limited capacity for filtration and sorption. Also, more sustainable alternatives are sought, due to the high carbon footprint of these materials. Biochar is a carbon-rich material produced by pyrolysis of biomass, and several types of biochar have been described as good sorbents and filter materials. Biochar is also a light and carbon negative material, which may fulfill other desired criteria for new green roof substrates. We here report on an experiment where two types of biochar, produced from olive husks at 450 °C or from forest waste at 850 ° C were mixed with volcanic rock or peat, and tested for retention capacity of phenanthrene and six heavy metals in a column experiment with unsaturated gravimetric water flow lasting for 3 weeks. The results suggest that biochar as a component in green roof substrates perform better than traditional materials, concerning retention of the tested pollutants, and that different types of biochar have different properties in this respect.

Rapid peat accumulation favours the occurrence of both fen and bog microbial communities within a Mediterranean, free-floating peat island.

The unique environment of a 4m-thick, free-floating peat island within the Posta Fibreno lake (Central Italy) was analyzed using DNA-based techniques to assess bacterial and fungal community members identity and abundance. Two depths were sampled at 41 and 279 cm from the surface, the former corresponding to an emerged portion of Sphagnum residues accumulated less than 30 yrs ago, and the latter mainly consisting of silty peat belonging to the deeply submerged part of the island, dating back to 1520-1660 AD. The corresponding communities were very diverse, each of them dominated by a different member of the Delta-proteobacteria class for prokaryotes. Among Eukaryotes, Ascomycota prevailed in the shallow layer while Basidiomycota were abundant in the deep sample. The identity of taxa partitioning between acidic surface layer and neutral core is very reminiscent of the differences reported between bogs and fens respectively, supporting the view of Posta Fibreno as a relic transitional floating mire. Moreover, some microbial taxa show an unusual concurrent species convergence between this sub-Mediterranean site and far Nordic or circumpolar environments. This study represents the first report describing the biotic assemblages of such a peculiar environment, and provides some insights into the possible mechanisms of its evolution.

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.

Posidonia oceanica (L.) based compost as substrate for potted basil production.

BACKGROUND: Peat is the main component of growing media but is also a non-renewable resource; therefore European policy strongly encourages the use of peat alternatives such as compost. Posidonia is a Mediterranean seagrass that produces very conspicuous onshore deposits that can be composted. In this study, a commercial green compost and a Posidonia residue-based compost were tested in order to assess their potential use as substitutes or complements to peat. RESULTS: All macro and micro-element concentrations of the substrates were positively and significantly related to the percentage of composts in the growing media. Plant grown on peat showed higher content of P, Ca, K, Na, Cu, Mn, Zn and Fe, and a slightly higher biomass production in comparison to compost-based growing media. In contrast, plants grown on compost-based substrates showed lower uptake of Cd and Cr than peat. CONCLUSION: The results indicate that both composts can be used as a complement to the peat for substrate preparation, especially at a rate of 30%. The Posidonia-based compost showed better productive results in comparison to the green one. Basil grown on the two compost-based media showed reduced absorption level of potentially toxic metals in comparison to peat.

Ptaquiloside in Pteridium aquilinum subsp. aquilinum and corresponding soils from the South of Italy: influence of physical and chemical features of soils on its occurrence.

The bracken fern Pteridium aquilinum (L.) Kuhn, one of the most common plant species on Earth, produces a wide range of secondary metabolites including the norsesquiterpene glucoside ptaquiloside (PTA). Several studies are present in literature about eco-toxicological aspects related to PTA, whereas results about the effect of growth conditions and soil properties on the production and mobility of PTA are sometimes conflicting and further investigations are needed. The aim of the present work is to investigate the occurrence and possible fate of PTA in soils showing different physical and chemical features, and collected in several areas of the South of Italy. The PTA content was determined in both soil and fern samples by GC-MS; both the extraction protocol and recovery were previously tested through incubation studies. Soils samples were also characterized from the physical and chemical points of view in order to correlate the possible influence of soil parameters on PTA production and occurrence. PTA concentration in P. aquilinum fern seemed to be significantly affected by the availability of nutrients (mainly P) and soil pH. At the same time, PTA concentration in soil samples was always undetectable, independent of the PTA concentration in the corresponding Pteridium samples and pedo-climatic conditions. This seems to suggest the degradation of the PTA by indigenous soil microbial community, whereas incubation studies underlined a certain affinity of PTA for both organic colloids and clay/silt particles.

Effect of compost and manure amendments on zinc soil speciation, plant content, and translocation in an artificially contaminated soil.

The addition of organic matter in soil can modify the bioavailability of heavy metals. A greenhouse pot experiment was carried out using an edible plant species Eruca vesicaria L. Cavalieri grown on an artificially contaminated soil with Zn (665 mg kg(-1)). In this study, the effect of compost at 20 t ha(-1) (C20) and at 60 t ha(-1) (C60), manure at 10 t ha(-1) (M10) and at 30 t ha(-1) (M30), and chemical fertilizers (NPK) on Zn fate in a soil-plant system was evaluated. At the end of the experiment, the main growth parameters and Zn content in plants were determined. In addition, Zn speciation in the soil was assessed using the original Community Bureau of Reference sequential extraction and diethylene triamine pentaacetic acid extraction. Zinc, though an essential element for plant growth, caused toxicity effects in plants grown on control and manure treatments, while in the compost treatments, plants showed no visual toxicity symptoms. The concentrations of Zn in roots were similar for all treatments, while significant differences were observed for shoots. In fact, in the compost treatments, plants showed the lowest Zn concentration in shoots. Zinc speciation seems not to be affected by the applied treatments. Indeed, Zn plant content and translocation to shoots seems to be affected. Compost amendments significantly reduced Zn content and translocation in comparison to other treatments.

Monitoring of Cr, Cu, Pb, V and Zn in polluted soils by laser induced breakdown spectroscopy (LIBS).

Laser Induced Breakdown Spectroscopy (LIBS) is a fast and multi-elemental analytical technique particularly suitable for the qualitative and quantitative analysis of heavy metals in solid samples, including environmental ones. Although LIBS is often recognised in the literature as a well-established analytical technique, results about quantitative analysis of elements in chemically complex matrices such as soils are quite contrasting. In this work, soil samples of various origins have been analyzed by LIBS and data compared to those obtained by Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES). The emission intensities of one selected line for each of the five analytes (i.e., Cr, Cu, Pb, V, and Zn) were normalized to the background signal, and plotted as a function of the concentration values previously determined by ICP-OES. Data showed a good linearity for all calibration lines drawn, and the correlation between ICP-OES and LIBS was confirmed by the satisfactory agreement obtained between the corresponding values. Consequently, LIBS method can be used at least for metal monitoring in soils. In this respect, a simple method for the estimation of the soil pollution degree by heavy metals, based on the determination of an anthropogenic index, was proposed and determined for Cr and Zn.

Comparative management of offshore posidonia residues: composting vs. energy recovery.

Residues of the marine plant posidonia (Posidonia oceanica, PO) beached in tourist zones represent a great environmental, economical, social and hygienic problem in the Mediterranean Basin, in general, and in the Apulia Region in particular, because of the great disturb to the bathers and population, and the high costs that the administrations have to bear for their removal and disposal. In the present paper, Authors determined the heating values of leaves and fibres of PO, the main offshore residues found on beaches, and, meantime, composted those residues with mowing and olive pruning wood. The final composts were characterized for pH, electrical conductivity, elemental composition, dynamic respiration index, phytotoxicity, fluorescence and infrared spectroscopic fingerprints. The aim of the paper was to investigate the composting and energy recovery of PO leaves and fibres in order to suggest alternative solutions to the landfill when offshore residues have to be removed from recreational beaches. The fibrous portion of PO residues showed heating values close to those of other biofuels, thus suggesting a possible utilization as source of energy. At the same time, compost obtained from both PO wastes showed high quality features on condition that the electrical conductivity and Na content are lowered by a correct management of wetting during the composting.

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.

Degradation and persistence of rotenone in soils and influence of temperature variations.

The persistence and degradation of rotenone and its primary degradation product 12a beta-hydroxyrotenone in soils were determined under standardized laboratory conditions in the dark at 20 or 10 degrees C and at 40% of water holding capacity. Degradation experiments were carried out on two types of soil collected in southern Italy, a silt clay loam (SCL) and a loamy soil (L). A kinetic model was developed to describe degradation rates of rotenone, taking into account the production, retention, and degradation of the main metabolites. The DT50 values of rotenone and 12a beta-hydroxyrotenone, were 8 and 52 days in SCL soil, and 5 and 23 days in L soil at 20 degrees C, respectively. However, at 10 degrees C a tendency for slower degradation of rotenone and 12a beta-hydroxyrotenone was observed (25 and 118 days in SCL and 21 and 35 days in L soils, respectively). The differences were significant for most data sets. Temperature had a strong effect on degradation; a 10 degrees C increase in temperature resulted in a decrease in the DT50 value by a factor of 3.1 and 2.2 in SCL and of 4.2 and 1.4 in L soils for both rotenone and 12a beta-hydroxyrotenone, respectively. Results show that the degradation rates of both rotenone and 12a beta-hydroxyrotenone were greatly affected by temperature changes and soil physicochemical properties. The degradation reaction fits the two compartment or the multiple compartment model pathways better, which clearly indicates a rather complex rotenone degradation process in soils. Results provide further insights on the rates and the mechanisms of rotenone degradation in soils, aiming to more clearly describe the degradation pathway of chemical residues in the environment.

Zinc distribution and speciation within rocket plants (Eruca vesicaria L. Cavalieri) grown on a polluted soil amended with compost as determined by XRF microtomography and micro-XANES.

Zinc distribution and speciation within different organs (root, petiole, and leaf) of the edible plant Eruca vesicaria L. Cavalieri were determined using synchrotron microbeam X-ray techniques (XRF microtomography and mu-XANES) for plants grown in polluted soil with or without compost amendment. Data on soil derived from different extraction procedures and using mu-XANES analyses on rhizospheric soil indicated that compost amendment did not significantly influence the Zn speciation and availability in soil. However, major differences were observed within the plants. Plants grown in the presence of compost were able to partly block zinc immediately outside the root endodermis in the form of zinc-phytate, while a smaller Zn fraction was allowed to xylem transport as zinc-citrate. In the leaves, zinc was largely excluded from leaf cells, and about approximately 50% was in the form of phosphate precipitates, and the other 50% was complexed by cysteine and histidine residues. The reported data provide new information concerning the mechanisms of zinc tolerance in E. vesicaria L. Cavalieri, a very common edible plant in Mediterranean regions, and on the role of compost in influencing the molecular strategies involved in zinc uptake and detoxification.

Photodegradation of rotenone in soils under environmental conditions.

An environmental fate study was performed to analyze the effects of soil components on the photochemical behavior of rotenone. Photodegradation experiments were carried out on three types of soil collected in southern Italy, Valenzano (VAL), Turi (TUR), and Conversano (CON), from April to June 2006. Soil thin-layer plates (1 mm thick) were spiked with 1.5 mg/kg of rotenone and exposed under natural conditions of sunlight and temperature. The plates were removed from the sunlight at predetermined intervals of continuous irradiation. Other soil samples, control and sterilized, were kept in the dark to evaluate possible effects of chemical and microbiological degradation during the irradiation experiment. The time for 50% loss of the initially applied rotenone varied from 5 to 7 h, following the order TUR < CON < VAL. In environmental studies, changes in temperature and/or moisture affected the degradation rate and caused deviations from first-order kinetics. The photolysis reaction fit the two compartment or the multiple compartment model pathways better. A fast initial decrease during the first 5 h of rotenone irradiation was followed by a much slower decline, which clearly indicates the rather complex chemical process of rotenone photodegradation on soil surfaces. Also, the degradation was shown to be directly related to the soil concentration of clay and organic matter. Rotenolone (12abeta-hydroxyrotenone) was detected by HPLC/DAD/MS analysis as the only photodegradation byproduct of rotenone in soil thin layers. Results provide additional insights on the rates and the mechanisms of rotenone degradation, aiming to describe more clearly the degradation performance of chemical residues in the environment.

Characterization of water extractable organic matter in a deep soil profile.

The aim of this study was to identify qualitative and quantitative differences of water extractable organic matter (WEOM) isolated from each horizon along a deep soil profile and to evaluate any relationship between the WEOC and the total organic carbon (TOC) content. The soil profile "Monte Pietroso" is located in the Murge area, Apulia region in Southern Italy. Samples from the eight horizons (Ap1, Ap2, Ab1, Ab2, Bt1, 2B, 2Bt2, and 2B/C) were collected in October 2002. The WEOM characterization was carried out by means of UV absorbance, fluorescence spectroscopy in the emission and excitation/emission matrix (EEM) modes, and additional spectroscopic derived indexes. Soil organic carbon was shown to accumulate in the top horizons (Ap) and, in general, to decrease with depth, whereas, the WEOM/TOC ratio increases with increasing depth. The aromaticity and the humification index of the WEOM decrease dramatically downward the soil profile, whereas the fluorescence efficiency index tends to increase markedly. The WEOM fractions feature three main fluorophores with different wavelength and relative intensity. In general WEOM transport phenomena are suggested to occur downward the soil profile, depending on the nature of the organic material and on the chemical and mineral characteristics of the various horizons.