Formation Of Organo-mineral Complexes Research Articles

Carbon Mineralization Controls in Top- and Subsoil Horizons of Two Andisols Under Temperate Old-Growth Rain Forest

The effect of mineral properties on soil organic carbon (SOC) destabilization processes is poorly known. Andisols developed under temperate old-growth rain forest store important amounts of SOC due to strong mineral adsorption capacity. We evaluated the effect of mineral soil properties on microbial activity and native SOC mineralization in an incubation experiment with and without the addition of labile organic carbon (C) and nutrients. Top- and subsoil horizons of two Andisols with contrasting age from temperate old-growth rain forest were sampled. We used the selective dissolution methods to determine the metals complexed with SOC and allophane content. Radiocarbon analysis activity was performed to determine the 14C activity and 14C ages of all soils as a proxy for SOC persistence. Additionally, we carried out a laboratory incubation under controlled conditions with and without 13C labeled cellulose and nutrient solution (NH4NO3, KH2PO4) addition. A lower microbial activity in the subsoils of both Andisols compared to topsoils in accordance with the lower 14C activity at depth was recorded. After cellulose and nutrient additions, both subsoils horizons showed native SOC mineralization after 80 days of incubation. In contrast, these amendments did not induce native SOC mineralization in topsoils showing differences on C turnover rates between top- and subsoil horizons. In both soils, the native SOC mineralization after labile C and nutrient additions was negatively related to Na-pyrophosphate extractable C and may therefore be controlled by the formation of organo-mineral complexes with increasing soil C age. We conclude that the physicochemical soil characteristics evolving during pedogenesis control the SOC stabilization and also destabilization processes in Andisols developed under temperate old-growth rain forests.

Structuring of High-Fine Mineral Particles to Prevent Wind and Water Erosion

The results of the study of the mechanism of structuring highly dispersed mineral particles by dust-pressing polymer solution StabOL are presented, using the example of overburden rocks of the Taseevsky, Baleisky and Kamensky quarries (Transbaikal Territory). Mineral and polymer-mineral samples were studied by differential scanning calorimetry, thermogravimetry, and infrared spectroscopy. The formation of intermolecular hydrogen bonds is confirmed by the shift of the absorption bands of the stretching vibrations of hydroxyl groups in the infrared spectra of polymer-mineral samples towards lower frequencies and a significant increase in the intensities of these absorption bands. It was found that structuring of mineral particles during their treatment with a polymer solution occurs through the formation of organomineral complexes as a result of intercalation, exfoliation (stratification) and adsorption of polymers. The important role of hydration layers and clay minerals in this process has been revealed.

Effect of adsorbed moisture on the pore size distribution of marine-continental transitional shales: Insights from lithofacies differences and clay swelling

The variation in pore water distribution within gas shale reservoirs has a significant effect on gas content, and thus on resource evaluation. However, the characteristics of water micro-distribution and its effects on pore parameters are still not well understood due to the mixed wettability of shale and the complexity of the pore structure. In this study, six lower Permian transitional shale samples from the southern North China Basin, humidified at four levels up to a relative humidity of 98%, were selected for moisture-equilibrated experiments and low-pressure N2 gas adsorption measurements. The results indicate that the adsorbed moisture in transitional clay-rich shales can be divided into capillary condensation water in the micropores and monolayer–multilayer adsorbed water in the non-micropores. Moreover, thermal maturity (VRo), total organic carbon, clay, and carbonate are positively correlated with the adsorbed moisture and micro-/mesopores, indicating that water in shales could be hosted in inorganic pores as well as in organic pores. Furthermore, the distribution of adsorbed moisture is mainly controlled by the VRo, component wettability (i.e., organic matter, clay, pyrite, and carbonate), and pore structure (micro-/mesopore distribution). In addition, a subtle adsorbed moisture may significantly reduce both the pore volume (PV) and specific surface area (SSA) of micropores, and the effect on micropores and SSA is more pronounced than that on the respective non-micropores and PVs. Additionally, the mechanism of clay swelling and pore expansion in clayey shale can provide certain insights for water–methane competitive adsorption, identifying clay type and pore size, and the formation of organo-mineral complexes.

Physicochemical transformation of expanded vermiculite after long-term use in hydroponics

Physicochemical properties of expanded vermiculite-phlogopite products from Kovdor (Murmansk region, Russia) used for 15 years as a hydroponics substratum were studied. The four investigated samples were as follows: natural vermiculite, initial expanded (roasted at 700 °C) vermiculite, spent expanded vermiculite and spent vermiculite roasted again at the same temperature. Data on the bulk density, field capacity, hygroscopicity, and expansion coefficients showed that the degradation of the substratum was accompanied by mechanical destruction, reduction of water absorption by half, and transformation of mineral phases. The structural transformation of expanded vermiculite was studied using X-ray diffraction (XRD), thermogravimetric analysis (TG), and differential scanning calorimetry (DSC), coupled with a mass spectrometric analysis of the released gases. Under conditions with a sufficient supply of plants with potassium of nutrient solution, a change in the mineral composition occurred: a decrease in the content of vermiculite and an increase in phlogopite. The formation of organomineral complexes on the surface of the vermiculite was detected. There was no noticeable change in the chemical composition of the expanded vermiculite during its use in hydroponics. In essence, the levels of potentially toxic elements (Mn, V, Ni, Cr, Co, Cu, Zn) met environmental regulations, and the levels of major elements (Mg, Ca, K, Fe, Mn) corresponded to those found in natural vermiculite. The chemical composition and structure of spent vermiculite allows its use as an ameliorant to improve soil, water, and air regimens.

Organic matter protection by kaolinite over bio-decomposition as suggested by lignin and solvent-extractable lipid molecular markers

The formation of organo-mineral complexes is essential in organic matter (OM) stabilization. However, limited studies have been conducted to systematically examine the mineral influence on the decomposition of plant residuals at a molecular level. In this study, pine needles and chestnut leaves were mixed with kaolinite at the weight ratio of 5:1. The controls were plant tissues without kaolinite. All the samples were incubated in the laboratory for one year. Molecular markers, including lignin-derived phenols (e.g. Vanilly units, syringyl units and cinnamyl units) and solvent-extractable lipids (e.g. n-alkanoic acid, n-alkanols and n-alkanes), were analyzed. The concentrations of lignin-derived phenols and lipid compounds were higher in the presence of kaolinite than without kaolinite. Lower degradation indexes, such as (Ad/Al)V (ratio of vanillic acid to vanillin) and CPI (carbon preference index of n-alkanoic acid and n-alkanes), were found in the kaolinite system. These results indicate that kaolinite reduced the OM decomposition. The addition of kaolinite also stabilized some carbohydrates from plants. Furthermore, the degradation of OM led to the generation of persistent free radicals, indicated by electron paramagnetic resonance (EPR) signals. The EPR signals were higher with than without kaolinite. We hypothesize that the adsorption of semiquinone or quinone radicals on kaolinite may limit their reaction with other OM moieties and thus extended their lifetimes. In addition to embedding OM in soil aggregates, our results provide direct evidence of another mineral protective mechanism of soil OM.

Oxalate Enhances Desorption of Perfluorooctane Sulfonate from Soils and Sediments

Perfluorooctane sulfonate (PFOS) is one of the most widespread toxic substances in water distribution systems, posing a significant risk to public health and the environment due to its toxic and non-biodegradable nature. In this study, the effect of oxalate on PFOS adsorption/desorption to/from soil and sediment samples was studied with batch experiments. Dissolved organic carbon content in soil strongly enhanced the retention of organic halogens. Oxalate increased PFOS desorption by 1.43- to 17.14-fold and significantly increased the release of dissolved organic carbon and inorganic ions in soils. The effects of root exudates were similar to those of oxalate. Addition of low molecular weight dissolved organic carbon caused partial dissolution of the soil structure (e.g., through formation of organo-mineral complexes), resulting in the release of organic carbon and metal ions and subsequently enhancing PFOS desorption. The effects of oxalate on organic halogen desorption were influenced by dissolved organic carbon content and formation of calcium oxalate.

Effect of aluminium on mineralization of water extractable organic matter and microbial respiration in southern temperate rainforest soils

To date the effect of aluminium (Al) on carbon (C) mineralization has not been extensively studied in Chilean temperate rainforests. Here, we examine to what extent the C mineralization of water extractable organic matter (WEOM) and mineral Ah horizon are affected by differing molar ratios of Al and C (Al:C). It has been postulated that an increase in the concentration of Al in the soil solution does not affect the mineralization of WEOM and Ah horizon until a Al:C threshold is reached, at which point mineralization decreases. We hypothesized that dissolved organic C binds Al that is otherwise toxic to soil microorganism in the soil solution. Subsequently, the organic C remaining is mineralized or lost in water sheds. A microcosm experiment was designed where Al was added to WEOM or Ah horizon (0–8 mg L−1 or kg−1). Potential biodegradation was evaluated by trapping CO2 emitted during 15 days of incubation. Additionally, the amount of living fungal cells in the WEOM and microbial biomass of Ah horizon were quantified. The Al complexation was determined by selective dissolution, and characterized by infrared spectroscopy. In general, the carbon mineralization rates and the amount of fungal cells of WEOM were similar to that of the control (0 Al addition) when the Al:C ratio was <0.16. With increasing Al concentrations, mineralization was reduced up to 80%, accompanied by the formation of organo-mineral complexes, as indicated by infrared analysis. We conclude that Al exerts fine regulation on C availability necessary for microbial growth in both, WEOM and the Ah horizon.

Microagrogenesis of chernozem in agrocenosis

The aim of the study was to provide scientifi c and theoretical substantiation for the process of microaggrega- tion of typical chernozem via the simulation of natural processes of soil formation under the effect of systemat- ic application of soil-protecting technologies of crop cultivation with surface packing of root and after-harvest remains, humus, and mineral fertilizers in agrocenoses of the Left-Bank Forest-Steppe of Ukraine. Methods. Laboratory-analytical, experimental fi eld, statistical. Results. During tillage (for over 75 years) the number of free and friable-linked aggregates in the 0–40-cm chernozem layer decreased down to 17–20 %, and on the background of organic-mineral system of fertilization (15 t/ha of humus + N 80 P 75 K 60 ) there was an increase in the content of the mentioned groups of microaggregates up to 20–25 %. The systematic implementation of soil protective technologies promoted the increase in the content of free and friable-linked microaggregates up to 29–32 %. During tillage, the coeffi cient of saturation with humus for physical clay (PC) decreased 1.3–1.4 times compared to the grassland. The value of PC saturation during the soil protective tillage was optimal, as humus was neither accumulated in the form of free humates, nor stored like “fat” in animal organisms.aAnd there was no blocking of nutrients with free humates. Humus acts as a connective tissue, promoting the improved water-resistance of chernozem structure on the micro- and macroaggregate levels. The ability of chernozems to have aggregation was determined by the dispersion factor (DF), which was 12–14 % during tillage without introducing any fertilizers, and 10 % – with the introduction of fertilizers, which testifi ed to a weak degree of microaggregation. With minimal tillage on the background of the organo-mineral system of fertilization, DF = = 6–7 %, and by the end of rotation it decreased down to 3-5 %. Conclusions. Enhanced microaggregation in soil protective technologies is explained by the fact that detritus and newly formed humic substances enhance their role in the formation of organo-mineral complexes in case of optimization of hydrothermal conditions in the seasonal cycle and decreased tempo of humus mineralization. The correlation coeffi cient between the num- ber of microaggregates, sized 0.01–0.25 mm and the content of peptized humic substances during tillage was as follows: R = +0.480.01, and for soil protective technologies it was: R = (+0.70–0.75) 0.01. The increase in microaggregation in conditions of soil protective tillage occurred in the direction of wild land analogs and fallow, which testifi ed to the simulation of the natural process of typical chernozem microaggregation in the agrocenoses of the Left-Bank Forest-Steppe of Ukraine.

Response of different soil organic matter pools to biochar and organic fertilizers

A full understanding of the agronomic and environmental potential of biochar, and especially its potential as a C sequestration strategy, requires a full comprehension of its effects on native soil organic matter (SOM), as well as of its interactions with other organic amendments co-applied to the soil. In a field experiment, we investigated changes in quantity and quality of SOM pools characterized by different protection mechanisms as affected by 20tha−1 of biochar added alone or combined with two different organic fertilizers (i.e., municipal solid waste compost and sewage sludge) 8 months after application. In particular, free, intra-macroaggregate, intra-microaggregate, and mineral-associated SOM fractions were separated and analyzed for organic C, total N, and stable isotopic ratios; further, diffuse reflectance infrared Fourier transform spectroscopy was used to examine functional group composition. Soil biomass C content, basal respiration, and metabolic quotient were also determined. Biochar and organic fertilizer application increased significantly SOM content. Biochar accumulated mainly in the free SOM pool, not protected by the soil mineral matrix. Especially noteworthy was the significant interaction effect found between the biochar and organic fertilizer factors on mineral-associated organic C content. This suggested a promoting action of biochar on C stabilization in organically-fertilized soils through the formation of organo-mineral complexes. Organically-fertilized soils had higher microbial C than unfertilized soils. Basal respiration and metabolic quotient, however, were not affected by any of the treatments. As a whole, our results support the potential of biochar application as a strategy to sequester C in soils.

Formation of organo-mineral complexes as affected by particle size, pH, and dry - wet cycles

The formation of organo-mineral complexes is an important process controlling carbon cycling and the properties of soil particles. However, differences between the complexes formed in aqueous systems and those found in terrestrial systems have not been clearly recognised. This study simulated the formation of organo-mineral complexes between dissolved humic acid (DHA) and mineral particles using a solid/aqueous adsorption experiment (aqueous system) and a wet–dry cycling methodology (terrestrial system). The clay fraction of mineral particles contributed greatly (&gt;90%) to overall DHA adsorption on soil particles in adsorption experiments where DHA fractionation was clearly observed. Aromatic content was found to be less favourable for adsorption under all conditions. For particles of different sizes, the significance of fractionation increased with adsorption. High adsorption was observed under acid conditions, although there was less fractionation as a result of the acid-facilitated ligand exchange process. When using a wet–dry cycling methodology, a much higher fOC was observed for the complexes than when using the adsorption experiment, and DHA fractionation was not significant. Further, the distinctly decreased E465/E665 ratio suggests that the DHA washed off from acid complexes was different from the original DHA and most likely the result of DHA precipitation during wet–dry cycles under acid conditions.

Electrolytic conductivity of synthetic organomineral complexes

The mechanism of the formation of organomineral complexes in soils is very complex and still little known. Examination of the complexes in unaltered form, as isolated from the soil, is very difficult due to the dispersing effect of all extraction agents which break the complexes up, destroying their natural properties. It is much easier to perform most of the tests on preparations of organomineral complexes obtained under laboratory conditions. This paper is concerned with model research on the formation of synthetic complexes of humic acids with minerals: Na-montmorillonite, mica, kaolinite at various pH values (3-7) and in the presence of aluminum ions. The aim of the research was to develop an optimum reaction of suspension for the synthesis of organomineral complexes, to study the role of aluminum ions, and to attempt to determine the degree of their complexity on the basis of the electrolytic conductivity (EC). An important influence of the suspension pH value on the value of EC was observed. The greatest correlation was found in the organomineral preparations with kaolinite and with aluminum (r = 0.93***). Generally, it can be stated that the degree of reaction of humic acids with minerals depended most of all on the type of mineral, on the pH value, and on the presence of aluminum.

Humic substances along the profile of two Typic Haploxerert

In Vertisols, organic matter contributes to soil colour by formation of organo-mineral complexes and affects morphological, physico-chemical, biological and biochemical properties. Turbation may affect the chemical and structural composition of the most stabilised fractions of soil organic matter (SOM), i.e., humic substances (HS). The objectives of this study were to: (1) characterise SOM in two Vertisols (V1 and V2) developed under Mediterranean climate in Italy, using some HS characteristics as indicators of SOM turnover in Vertisols, and (2) explore possible differences related to the pedomorphologic conditions of the area under which two soils have formed. SOM evolution along the soil profile was investigated by applying different techniques to chemically extracted HS. Humification parameters, thermal methods, such as Differential Scanning Calorimetry (DSC) and Thermogravimetry (TG) together with isoelectric focusing (IEF) were used. The results showed a significant difference in the chemical characteristics of SOM in the considered Vertisols. A higher amount of total and humified carbon was found in pedon V2. In particular, the results indicated an accumulation of humified compounds in deeper horizons of V2: this effect is particularly significant since both soils were under the same agricultural management and the same climatic conditions, but were different in physiografic position, slope and colour. The higher amount of not humified SOM in the pedon V1 could explain the differences found in the shape and size of soil structure between the two pedons. The different SOM evolution occurring in the two Vertisols apparently influenced the structure and composition of the HS fraction. Thermal analysis and isoelectric focusing data provided evidence of a different level of stabilisation of HS from the two Vertisols. The HS from pedon V2 have a higher molecular weight structure, which would imply a higher level of SOM stabilisation. Conversely, HS in the pedon V1 appeared to be richer in aliphatic and phenolic structures, which may imply the presence of less stabilised HS fractions. These findings agree well with the different water dynamics occurring in the two sites, which confirmed the influence exerted by water on chemical and structural composition of HS and, consequently, their effect in determining Vertisols colour. In conclusion, thermal and isoelectric focusing characterisation of HS appear to shed some light in understanding the structural complexity of Vertisols. The results obtained in the present study, if confirmed on a larger number of Vertisols, suggest the possibility of using HS as indicators of SOM turnover in relation to pedomorphology, use and management of soils.

Carbon distribution in different compartments of forest soils

Three mineral A horizons from forest soils associated with the characteristic forest humus types mull, moder and mor were investigated. The suitability of several physical or chemical fractionation methods for the characterization of major humification processes was determined. The distribution and structures of organic carbon were analyzed after fractionation according to density (plant residues, organo-mineral complexes), aggregate-size (floatables, macro-, microaggragates, clay fraction), and the classical humus fractionation (fulvic acid, humic acid, humin fraction). The fractions obtained were characterized by elementary analysis, wet-chemical methods (CuO oxidation) and CPMAS 13C NMR spectroscopy. The classical humus fractionation method seems to produce fractions which are suitable for the investigation of humification processes of lignin in forest soils. The results from both physical and chemical fractionation methods suggest that the presence of soil macrofauna, especially earthworms, is of considerable importance in the formation of organo-mineral complexes and soil aggregates. The structural chemical characterization of individual fractions provides further information about humification processes in soils.