31^{31}P-NMR characterization of phosphorus fractions in natural and fertilized forest soils

The amount, quality, and turnover of soil P is influenced by climate and changes in soil management. The objectives of this study were to evaluate the influence of edaphic properties, mean annual precipitation, and P-fertilization on soil organic P. $^{31}$P-NMR spectroscopy was applied to investigate P forms of forest soils of the Central Western Spain. The concentrations of NaOH-extractable inorganic-P were significantly higher in fertilized than in natural soils. Monoester-P was the dominant organic-P species in both natural and fertilized soils, representing between 19 and 54% of NaOH-extractable P. The highest concentrations of monoester-P were observed in the soil with higher content of Fe oxides. The high charge density of monoester-P allows rapid adsorption on soil minerals and extensive interaction with sesquioxides that protect inositols from degradation. Diester-P represented between 3 and 17% of alkali-extractable P, reflecting a relatively low microbial activity in the soils on schists with a high content of Al and Fe oxides.Caractérisation du phosphore et de ses fractions par la technique du NMR dans des sols forestiers fertilisés et non-fertilisés. La teneur, la qualité et le turnover du P du sol sont influencés par le climat et les changements dans la gestion du sol. L'objectif de cette étude a été d'évaluer l'influence des propriétés édaphiques, de la pluviométrie moyenne annuelle et de la fertilisation phosphatée sur le P organique du sol. La spectroscopie NMR a été appliquée pour rechercher les formes du P dans des sols forestiers du Centre Ouest de l'Espagne. La concentration en P inorganique extrait avec NaOH a été significativement plus haute dans le sol fertilisé que dans le sol naturel. Le monoester phosphorique (représentant entre 19 et 54 % du P extractable avec NaOH) est la forme dominante de P organique, aussi bien dans le sol naturel que dans le sol fertilisé. La plus haute concentration de monoester phosphorique a été observée dans le sol avec la plus haute teneur en oxydes ferriques. La haute densité de charge du monoester phosphorique permet sa rapide adsorption sur les composés mineraux du sol et son interation marquée avec les sesquioxydes, protégeant ainsi de la dégradation les inositols. Les diesters phosphoriques représentent entre 3 et 17 % du P extractable avec NaOH, montrant par là une relativement basse activité microbienne dans les sols sur schistes avec une haute teneur en oxydes aluminiques

Industrial carbon input to arable soil since 1958

Tracing the history of industrial fossil fuel combustion on the carbon stock in soil is challenging, since it is mixed with other soil organic carbon (SOC). Isolation of black carbon (BC) yields a mixture of diagenetic fossil C and pyrogenic BC from biomass and fossil fuel combustion. We investigated the degree to which fossil fuel combustion emissions have contributed to SOC and BC and how deposition dynamics have changed in the last century. As only biomass-derived BC contains C-14, we determined the content and C-14 signature of the benzene polycarboxylic acid (BPCA) fraction as the product of total BC oxidation. From an isotopic mass balance model, the proportion of fossil BC deposition and its contribution to SOC was calculated. Soil samples were taken from 1958-2002 from a long term agricultural field experiment in Halle, Germany; the area represents one of the most productive lignite mining areas in the world. Between 1958 and 1971, total BC content increased significantly (1.9 +/- 0.1-2.30 +/- 0.06 g/kg soil), and the BC-specific radiocarbon content decreased from 29.6 +/- 0.4 to 26.9 +/- 0.2 pMC, corresponding to 1.35 +/- 0.07 and 1.8 +/- 0.08 g/kg BC from diagenetic C and fossil fuel combustion (denoted here as fossil BC). We infer an increase in fossil BC content of 30% within this timespan, with a net input rate of 9 g/m(2) yr. In the 1970s, after railway electrification, reduction of lignite mining and related heavy industries, fossil BC deposition to soil was no longer significant. Overall, about 120 g/m(2) fossil BC was deposited between 1958-1971, with 390 g/m(2) before 1958. Fossil BC contributed ca. 75% of total BC and 15% SOC to arable soil, without any significant change in the following 30 yr (1971-2002). (C) 2015 Elsevier Ltd. All rights reserved

Extracellular Polymeric Substances from <i>Bacillus subtilis</i> Associated with Minerals Modify the Extent and Rate of Heavy Metal Sorption

Extracellular polymeric substances (EPS) are an important source of organic matter in soil. Once released by microorganisms, a portion may be sorbed to mineral surfaces, thereby altering the mineral̀s ability to immobilize heavy metals. EPS from <i>Bacillus subtilis</i> were reacted with Ca-saturated bentonite and ferrihydrite in 0.01 M KCl at pH 5.0 to follow the preferential uptake of EPS-C, -N, and -P. The sorption kinetics of Pb²⁺, Cu²⁺, and Zn²⁺ to the resulting EPS-mineral composites was studied in single and binary metal batch experiments ([metal]_total = 50 μM, pH 5.0). Bentonite sorbed much more EPS-C (18.5 mg g^–1) than ferrihydrite (7.9 mg g^–1). During sorption, EPS were chemically and size fractionated with bentonite favoring the uptake of low-molecular weight components and EPS-N, and ferrihydrite selectively retaining high-molecular weight and P-rich components. Surface area and pore size measurements by N₂ gas adsorption at 77 K indicated that EPS altered the structure of mineral-EPS associations by inducing partial disaggregation of bentonite and aggregation of ferrihydrite. Whereas mineral-bound EPS increased the extent and rate of Pb²⁺, Cu²⁺, and Zn²⁺ sorption for bentonite, either no effect or a decrease in metal uptake was observed for ferrihydrite. The extent of sorption always followed the order Pb²⁺ > Cu²⁺ > Zn²⁺, which also prevailed in binary Pb²⁺/Cu²⁺ systems. In consequence, sorption of EPS to different minerals may have contrasting consequences for the immobilization of heavy metals in natural environments by inducing mineral-specific alterations of the pore size distribution and, thus, of available sorption sites