Showing papers by "Nicola Senesi published in 2010"

Dissolved Organic Matter Extracted With Water and a Saline Solution From Different Soil Profiles

Abstract: The organic matter fraction present in soil solution and passing a filter of pore size of 0.45 μm is operationally defined as dissolved organic matter (DOM). In this work, DOM was extracted with either water or a saline solution from the various horizons of four different soil profiles, either cultivated or not, and characterized by chemical analysis and spectroscopic techniques such as emission fluorescence spectroscopy and Fourier transform infrared spectroscopy. Water and a saline solution extracted different amounts of DOM. These results imply that the effect of colloidal dispersion exerted by water resulted in a higher release and solubilization of organic matter compared with colloidal flocculation exerted by the saline solution. Thus, the extractant used for DOM extraction from soil must be taken into due account for its effect on the nature of DOM extracted. Our results corroborate the need to standardize extraction methods. Fluorescence emission spectra provided evidence of a variation in DOM composition as a function of depth along the soil profile, which was possibly related to adsorption of aromatic molecules on soil colloids. Finally, land use also seemed to influence the chemical nature of DOM along the soil profile.

Chemical Structure of Soil Organic Matter in Slickspots as Investigated by Advanced Solid-State NMR

Abstract: Slickspot soils are saline, and knowledge of their humic chemistry would contribute to our limited understanding how salinity affects soil C and N stocks. We characterized humic acids (HA) from slickspot soils with solid-state l3C nuclear magnetic resonance (NMR). Expanding on previous use of cross polarization/magic angle spinning (CP/MAS) NMR, we used direct polarization (DP) and yet more ad­ vanced spectralediting techniquesto identifyspecificfunctionalgroups, detect the connectivities of different functional groups, and selectively observe fused ring carbons. A series of soil HA was extracted from soil layers having different physical properties: silt texture, vesicular struc­ ture, and clay texture. They were compared with HA from correspond­ ing depths in soils adjacent to the slickspots. All HA consisted of five main structural components: aliphatic chains,peptides, sugar rings,lignin residues, and aromatics/olefinics. For all soils, except one outside slick­ spots, the HA from the vesicular and clay layerscontainedless nonpolar alkyls and more aromatics than those from surface silt layers, but their spectral proportions differed when the l3CNMR was performedusing CPIMAS instead of DP Humic acids from the surface layers inside the slickspots had lower aromaticity than those from outside the slickspots. Advanced spectral editing techniques allowed for the selection of non­ protonated carbons and mobile groups, alkyls, CH, and CH2 groups, which would otherwise be buried in the heavily overlapped spectrum. They providedmore structural information than was obtainedby routine l3CCP/MAS or DP

Humic Substances as Natural Nanoparticles Ubiquitous in the Environment

Abstract: Humic substances (HS) are recognized to be the most widespread and ubiquitous components of natural nonliving organic matter (NOM) in the global environment The estimated level of soil organic carbon (SOC) on the earth surface occurring as HS is 30 × 1014 Kg In particular, approximately 60%∼70% of the total SOC has been estimated to occur in HS These substances consist of a physically and chemially heterogeneous mixture of relatively high-moleular weight, yellow to black organic compounds of mixed aliphatic and aromatic nature, formed by secondary synthesis reactions (humification) of products of the microbial and chemical decay and transformations of biomolecules released from organisms into the surrounding environment both during life and after death The HS are universally recognized as the most relevant and chemically, biologically and physically active components of NOM thanks to their typical composition, macromolecular structure, polyfun-tionality, surface properties, presence of multiple reactive sites, variable sizes and shapes, and intrinsic porosity

Germination and Early Growth of Slickspot Peppergrass (Lepidium papilliferum) as Affected by Desert Soil Humic Acids

Abstract: Slickspot peppergrass (Lepidium papilliferum) is a biennial, or possibly perennial, endemic plant growing in the Southern Idaho high desert in visually distinct small-scale depressions in soils that collect water (so-called slickspots). Lepidium papilliferum establishes seed banks not germinating the first year but remaining dormant and viable for several years. Humic acids (HA) are universally considered to be the most important, abundant, and biologically and chemically active fractions of soil organic matter and are known to affect plant growth by various mechanisms, depending on their origin, nature, and concentration. The effects of HA in slickspot soils and how they relate to the possibility of being a factor in restoring native plants is only partially known. Thus, the objective of this study was to identify and evaluate the effects of HA isolated from three different layers within the soil profile (silt, vesicular, and clay) from inside a representative slickspot on the germination and early growth of slickspot peppergrass. Furthermore, these effects were tentatively related to the chemical, physicochemical, compositional, structural, and functional characteristics of the HA. Results of statistical analysis showed that both the type and concentration of the three HA examined exert a highly significant or significant effect on the germination and early growth of slickspot peppergrass as a function of the soil depth from which the HA originated in the slickspot. In particular, germination seemed to be enhanced, especially at higher concentrations, by the less hydrophobic HA, rich in oxygen and total sugars, present in the bottom clay soil layer, whereas root growth and shoot growth were positively influenced by the more hydrophobic and probably more polycondensed HA, rich in C, H, N, and phenolic OH present in the top layer rich in silt.

Phytotoxicity assay of selected plants to pyrene contaminated soil.

Abstract: Three selected plants (Alfalfa, oilseed rape and perennial ryegrass) were tested for their ability to germinate and grow in a soil contaminated with a typical polycyclic aromatic hydrocarbon (PAH), Pyrene, at two concentrations: 50 mg/kg or 100 mg/kg dry soil. When compared to control plants grown in uncontaminated soil, pyrene did not inhibit the germination of the three tested species even at the highest concentration (100 mg/kg), with a germination percentage of alfalfa, oilseed rape and ryegrass of 95, 90 and 86%, respectively. The shoot and root lengths of the three plants were also unaffected by the presence of pyrene at both concentrations. Based on these results, the three tested species can be considered as pyrene tolerant plants, and can be used in phytoremediation experiments. Among the tested species, oilseed rape seemed to be the most suitable plant, probably because of the greater root length. Greenhouse studies are in progress to evaluate the development of these plants in the advanced growth stages, and their effect on pyrene level in soil.