Organic Matter-rich Soil Research Articles

Molecular Mechanisms of Plant Responses to Copper: From Deficiency to Excess.

Copper (Cu) is an essential nutrient for plant growth and development. This metal serves as a constituent element or enzyme cofactor that participates in many biochemical pathways and plays a key role in photosynthesis, respiration, ethylene sensing, and antioxidant systems. The physiological significance of Cu uptake and compartmentalization in plants has been underestimated, despite the importance of Cu in cellular metabolic processes. As a micronutrient, Cu has low cellular requirements in plants. However, its bioavailability may be significantly reduced in alkaline or organic matter-rich soils. Cu deficiency is a severe and widespread nutritional disorder that affects plants. In contrast, excessive levels of available Cu in soil can inhibit plant photosynthesis and induce cellular oxidative stress. This can affect plant productivity and potentially pose serious health risks to humans via bioaccumulation in the food chain. Plants have evolved mechanisms to strictly regulate Cu uptake, transport, and cellular homeostasis during long-term environmental adaptation. This review provides a comprehensive overview of the diverse functions of Cu chelators, chaperones, and transporters involved in Cu homeostasis and their regulatory mechanisms in plant responses to varying Cu availability conditions. Finally, we identified that future research needs to enhance our understanding of the mechanisms regulating Cu deficiency or stress in plants. This will pave the way for improving the Cu utilization efficiency and/or Cu tolerance of crops grown in alkaline or Cu-contaminated soils.

Biosolids management and utilizations: A review

Biosolids, derived from wastewater treatment processes, have garnered increasing attention as a valuable resource due to their rich organic and inorganic constituents, which can be beneficially utilized in multiple sectors, including agriculture, civil engineering, and energy recovery. The present review article begins by providing an overview of biosolids, including their production methods and classification based on treatment processes. Subsequently, the chemical composition of biosolids is explored, highlighting the diverse array of organic and inorganic components present. The characterization techniques employed for analyzing biosolids, such as spectroscopy, chromatography, and microscopy, are thoroughly discussed, emphasizing their role in determining the quality and suitability of biosolids for different applications. Furthermore, the environmental impacts associated with biosolids disposal are extensively examined. This includes the potential risks posed by heavy metals, pathogens, and emerging contaminants, as well as strategies for mitigating these risks through proper treatment and management practices. In addition to environmental considerations, the article explores the various products that can be derived from biosolids. These include organic matter-rich soil amendments for agricultural applications, inorganic nutrient supplements for enhancing plant growth, and the potential for energy recovery through anaerobic digestion and thermal conversion technologies. The utilization of biosolids in civil engineering projects, such as landfill capping and construction materials, is promising. Land application of biosolids also can have economic and waste management benefits (e.g., conservation of landfill space; reduced demand on non-renewable resources like phosphorus; and a reduced demand for synthetic fertilizers).

Effect of natural organic matter on Cr(VI) reduction by reduced nontronite

Fe(II)-bearing clay minerals are abundant in soils and are critical to control the fate of the highly toxic hexavalent chromium (Cr(VI)). Even though the reduction of Cr(VI) by Fe(II)-bearing clay minerals has been extensively studied, the effect of the commonly co-existing natural organic matter (NOM) on this process is poorly understood. This study aimed to understand the kinetics of Cr(VI) reduction by a typical Fe(II)-bearing clay mineral (i.e., reduced nontronite (rNAu-2)) in the presence of Suwannee River NOM and to unveil the possible mechanisms. Cr(VI) reduction experiments were conducted with different NOM concentrations in a range of 0 to 100 mg C L−1 under circumneutral pH. The time-course aqueous-phase measurements and solid-phase characterizations were performed with a combination of wet chemical methods, transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses. The results demonstrated that NOM inhibited Cr(VI) reduction overall, mainly due to the decrease of Cr(VI) sorption on rNAu-2 by mineral-bound NOM. Besides the predominant solid Cr(III) species, soluble and mobile Cr(III) complexes were formed during reduction. Interestingly, the reduction rate (k) decreased with the increase of NOM concentration from 0 to 20 mg C L−1, but kept increasing when the concentration of NOM increased from 30 to 100 mg C L−1. The contrary pattern is due to the increasing promotion effects that offset the inhibitory effect caused by competitive sorption between Cr(VI) and NOM. The promotion effects may include weakening the mineral passivation by forming stable aqueous NOM-Cr(III) complexes, accelerating the electron transfer rate by dissolving rNAu-2, and donating electrons through NOM-Fe(II/III) complexes and/or NOM-Cr(V) complexes. This study extends our knowledge of Cr(VI) reduction by clay minerals in organic matter-rich soils and sediments and has important implication for understanding the transport and long-term behavior of Cr in the environment.

Processes controlling the organic matter degradation in a tropical coastal wetland: Mboro, Senegal

The Northern coastline, from Kayar to Saint Louis (Senegal) is characterized by a succession of dunes and inter-dunes. Coastal wetlands located in the inter-dunes which bear Organic Matter (OM) rich soil where market garden agriculture is the main activity. These zones locally called “Niayes” are characterized by shallow groundwater table threatened by anthropogenic pressure, climate and environmental impacts. The scientific interest of this research work is to characterize the composition of soil OM to discuss its origin, composition, and diagenetic evolution in this depositional environment of Mboro research site with regard to natural and anthropogenic pressure. Three selected core samples with depth interval of 5 cm aligned in along a slope transect in the Mboro wetland were carried out. Soil OM were analyzed for Particulate OM, C/N, Rock-Eval HI and OI, δ13C, δ15N whereas sediments and water were respectively analyzed for grain size distribution, water contents and redox potential down to 50 cm depth. We have demonstrated through the results a vertical variability in the content, the nature and preservation quality of sedimentary OM with the occurrence of a peat storage zone. The isotopic markers depict a strong contribution of C3 plants, macrophytes and to a lesser extent of algae and microbial organic materials. High concentrations of dissolved nutrients occurring mainly on the surface slope may derive from the use of fertilizers to improve agricultural yields. These results constitute an added value in the scientific knowledge of this sector of the Niaye of Senegal.

Influence of different types of nanomaterials on soil enzyme activity: A global meta-analysis

Engineered nanomaterials (NMs) have been widely used and could be released to soil environments, yet a consensus has not been reached on how soil enzyme activity, one of the most important indicators of soil health, responds to NMs exposure. Here, a global meta-analysis of 73 studies was carried out to examine the influence of NMs exposure on soil enzyme activity. Our results showed that the NM type was the most decisive factor, as Ag and Cu NMs had significant negative effects on soil enzyme activity. Carbon (C) NMs showed a negative effect on microbial biomass carbon (MBC) and most enzymes except dehydrogenase and soil respiration. Ti NMs only reduced soil respiration and urease activity. Zn NMs exerted no negative effect on all tested enzymes except dehydrogenase. Fe NMs had no negative effect on all tested enzymes, but stimulated the activity of acid phosphatase. The results also revealed that the response of β-glucosidase and dehydrogenase to NMs were similar to soil MBC and soil respiration, respectively. In addition, the inhibition of C, Ag, and Cu NMs on enzymes increases with dose. The exposure duration also regulated the effect of NMs on enzymes, which decreased with exposure longer than 10–20 days. Effects of NMs are also highly dependent on soil properties, for instance, the effect of Ag NMs on soil enzyme activity was weaker in organic matter-rich soils (>2%) or acidic soils (pH <7). Our meta-analysis suggests that soil enzyme activity could be negatively impacted by specific NMs, such as Ag, Cu, and even C NMs, of which high dose and prolonged exposure should be prevented, especially in low organic matter and/or neutral-alkaline soils. Therefore, these results can provide insights into the guideline for the future design and potential safe use of certain NMs, such as Zn and Fe NMs.

Phenoloxidase activity and organic carbon dynamics in historic Anthrosols in Scotland, UK.

Phenolic compounds are chemical precursor building blocks of soil organic matter. Their occurrence can be inhibitory to certain enzymes present in soil, thereby influencing the rate of decomposition of soil organic matter. Microbe-derived phenoloxidases (laccases) are extracellular enzymes capable of degrading recalcitrant polyphenolic compounds. In this study, our aim was to investigate the relationships between phenoloxidase enzyme activity, organic carbon content and microbial abundance in the context of long-term anthropogenically amended soils. To achieve this, we used a series of complementary biochemical analytical methods including gas chromatography, enzyme assays and solid-state Carbon-13 Cross Polarisation Magic-Angle Spinning Nuclear Magnetic Resonance Spectroscopy (13C CPMAS NMR). Using several anthrosols found in St Andrews (Scotland, UK) that had been subjected to intense anthropogenic modification since the medieval period (11th century AD) to present-day, we were able to scope the impact of past waste disposal on soils. The long-term anthropogenic impact led to organic matter-rich soils. Overall, phenoloxidase activity increased by up to 2-fold with soil depth (up to 100 cm) and was inversely correlated with microbial biomass. Solid-state 13C NMR characterisation of carbon species revealed that the observed decline in soil organic matter with depth corresponded to decreases in the labile organic carbon fractions as evidenced by changes in the O/N-alkyl C region of the spectra. The increase in phenoloxidase activity with depth would appear to be a compensatory mechanism for the reduced quantities of organic carbon and lower overall nutrient environment in subsoils. By enzymatically targeting phenolic compounds, microbes can better utilise recalcitrant carbon when other labile soil carbon sources become limited, thereby maintaining metabolic processes.

Soil cadmium mobilisation by dissolved organic matter from soil amendments

Dissolved organic matter (DOM) release from Cd contaminated soils been linked to mobilisation of the metal as Cd-DOM complexes and this may be exacerbated by organic matter-rich soil amendments. The quantity and quality of the DOM can determine the proportion of dissolved Cd that partitions to mobile complexes and their stability and, thus, the potential for Cd transport from contaminated soils. The aim of this work was to examine differences in Cd mobilisation from soils to which different types of soil amendments/conditioners have been applied and the importance of DOM characteristics in determining the extent to which this can happen. Three soils were spiked with Cd to 2 mg kg−1, allowed to equilibrate and then treated with compost and peat. These soils and an untreated subsample of each soil were then adjusted to three different pHs: 5.6, 6.4 and 7.4, using lime. The amount of Cd mobilised from each soil was tested using a column leaching experiment. Ultrafiltration and speciation modelling were used to determine amounts of Cd as DOM-complexed, “truly” dissolved (<5 kDa) and colloidal species, while DOM quality was assessed using UV–Vis and fluorescence spectroscopy. Most colloidal Cd was mobilised from the compost treated soils (50%–60%), followed by the peat treated soils (20–44%). The relationships between colloidal Cd, DOC concentration and soil pH, together with the spectroscopic and modelling results showed that structural properties of DOM are an important factor in mobilising Cd from contaminated soils.

A carbon-sink in a sacred forest: Biologically-driven calcite formation in highly weathered soils in Northern Togo (West Africa)

Soil organic matter (OM) is a source of fertility for food provisioning and a means for climate mitigation. A high pedodiversity observed over very short distances due to both past and present land use, such as in Western Africa (Northern Togo), makes this a crucial issue. In particular, some small spots covered by sacred forests (forêts sacrées) of high cultural value in this area are extremely biodiverse, calcareous and high in OM in contrast with the non-calcareous, poor OM, overgrazed woody savannah and agricultural surroundings. The objectives of our work were to understand this pedodiversity and the process of CaCO3 formation in the soil under the highly biodiverse forest using morphological, micromorphological, chemical and mineralogical soil analyses. The results show a high degree of weathering of the gneiss parent material, presence of plinthite gravels, dominance of 1:1 clays, formation of swelling clays in the imperfectly drained soils, and low OM content. The presence of palygorskite, although in traces, suggests drier intervals and is consistent in this context with the extreme wet and dry climate conditions in the region. In the OM rich soils under forest, bio-calcification takes place in the form of CaCO3 needles, micrite hypocoatings around biopores and calcified cells. Oribatid excrements are associated with calcite and organic matter in the sacred forest soil, indicating that litter recycling has played an important role in the formation of calcite. We hypothesize that the high biological activity releasing CO2, formation of HCO3– and precipitation of CaCO3 due to the Ca2+ released by the recycled organic matter and weathering of plagioclases, lead to different forms of secondary calcium carbonate in the sacred forest soils. The high oxalate content of the vegetation in the sacred forest suggests that calcium carbonate formation, possibly via the oxalate-carbonate pathway, may also have played a role in calcite precipitation in these in organic matter rich soils. The parent material of these soils is not calcareous, meaning that these are not lithogenic carbonates, thus making them an important carbon sink. The soil characteristics indicate a high potential for development of the soils of the area in both agricultural yields and in potential carbon sequestration relevant to global change policies.

Intensive slurry management and climate change promote nitrogen mining from organic matter-rich montane grassland soils

AimsConsequences of climate change and land use intensification on the nitrogen (N) cycle of organic-matter rich grassland soils in the alpine region remain poorly understood. We aimed to identify fates of fertilizer N and to determine the overall N balance of an organic-matter rich grassland in the European alpine region as influenced by intensified management and warming.MethodsWe combined 15N cattle slurry labelling with a space for time climate change experiment, which was based on translocation of intact plant-soil mesocosms down an elevational gradient to induce warming of +1 °C and + 3 °C. Mesocosms were subject to either extensive or intensive management. The fate of slurry-N was traced in the plant-soil system.ResultsGrassland productivity was very high (8.2 t - 19.4 t dm ha−1 yr−1), recovery of slurry 15N in mowed plant biomass was, however, low (9.6–14.7%), illustrating low fertilizer N use efficiency and high supply of plant available N via mineralization of soil organic matter (SOM). Higher 15N recovery rates (20.2–31.8%) were found in the soil N pool, dominated by recovery in unextractable N. Total 15N recovery was approximately half of the applied tracer, indicating substantial loss to the environment. Overall, high N export by harvest (107–360 kg N ha−1 yr−1) markedly exceeded N inputs, leading to a negative grassland N balance.ConclusionsHere provided results suggests a risk of soil N mining in montane grasslands, which increases both under climate change and land use intensification.

Dose-related changes in respiration and enzymatic activities in soils amended with mobile platinum and gold

This study assessed the effect of amendment of Australian soils (acidic, organic matter, Fe-rich, alkaline and silt-rich soils) with mobile platinum and gold (0 to 2000 mg kg−1) on soil respiration and the activity of seven key soil enzymes. Platinum amendment significantly reduced soil respiration at almost all concentrations (p < 0.05) in all soils except in organic matter-rich soil where up to 2-fold stimulation occurred at concentrations of up to 500 mg kg−1. Amendments with mobile Au-complexes also inhibited soil respiration irrespective of soil type, except for the Fe-rich soil. Platinum and Au amendments also impaired enzyme activities across most concentrations and soils, except alkaline soils. Overall, while mobile Au appears to be somewhat more toxic to soil microbial communities than Pt, toxicity levels appear to be largely determined by soil properties.

Effects of afforestation of agricultural land with grey alder (Alnus incana (L.) Moench) on soil chemical properties, comparing two contrasting soil groups

BackgroundNatural afforestation of former agricultural lands with alder species is common in Europe. Symbiotic nitrogen fixation by actinomycetes associated with alder species has been widely used for improvement of soil properties of abandoned agricultural lands, but relatively little is known of the interactions of these processes with soil type and chemical composition. We conducted a space-for time study with soil sampling under and outside grey alder tree canopies on two different soil groups to explore effects of colonisation of former agricultural lands by alder on soil properties.ResultsThe results were analysed using analysis of variance. During the first 25 years after afforestation of former agricultural lands there was a significant increase in content of Ctot, Ntot, K+, Fe3+, Mn2+ and available P in the topsoil (0–10 cm and 11–20 cm) of Dystric Arenosols soils, which are deficient in organic matter. Such trends were not evident in organic matter rich Endostagnic Umbrisols soils, in which exchangeable K+ concentration decreased and exchangeable Fe3+ and Al3+ concentration increased.ConclusionsThe results show that the effects of grey alder on soil chemical properties depend on initial soil properties. The invasion of agricultural land by grey alder leads to spatial variability of soil chemical properties creating a mosaic pattern.

Temperature-induced iron (III) reduction results in decreased dissolved organic carbon export in subalpine wetland soils, Colorado, USA

Concentrations of dissolved organic carbon (DOC) in surface waters have rapidly increased across Europe and North America over the past few decades. The causes for such trends have yet to be fully understood, although several factors including elevated temperatures and decreased atmospheric deposition of acid, nitrogen and sulfur, are considered responsible for the release of carbon from soils into streams. In order to determine how seasonal temperature patterns and soil physical and chemical characteristics influence iron (Fe)(III) reduction and DOC release to pore-water in subalpine wetland soils, we measured potential Fe(II) and DOC export rates at low (6 °C) and high (18 °C) temperatures using flow-through reactors containing undisturbed wetland soils sampled in the Fraser Experimental Forest (Colorado, USA) in two wetland types and at two depths.Higher temperature, soil organic matter, nitrogen, and extractable Fe concentrations, but lower soil C:N ratios and extractable manganese concentrations promoted Fe(II) export from soil to water. Additionally, Fe(III) reduction was 1.5–5 times more responsive to temperature in shallow, organic matter-rich soils, compared to organic-poor deeper soils. Conversely, DOC export declined at higher temperature in all soils, consistent with a temperature-related increase in carbon respiration by Fe(III)-reducers. While higher temperature is expected to reduce carbon storage in wetland soils, our findings suggest that temperature-related increase in Fe(III) reduction will not generate additional release of DOC from soils to rivers.

Rhizosphere stochiometry, fruit yield, quality attributes and growth response to PGPR transplant amendments in strawberry (Fragaria × ananassa Duch.) growing on solarized soils

Plant Growth Promoting Rhizosphere microorganisms transplant amedements were tested for improving growth, yield, quality traits, runner production and rhizosphere stochiometry of strawberry cv. Chandler. The plants were grown on solarized and non-solarized organic matter rich soil. Exogenous root inoculation of six PGPR inoculants viz., Pseudomonas florescence, Bacillus subtilis, Azotobacter chroococcum, K-mobilizing bacteria and AM fungi were carried out in different combinations in a randomized completely block design with three replicates. The solarization was done with transparent plastic sheet. Application of 250 g PGPRs consourtium along with soil solarization significantly improved vegetative growth traits, rhizosphere microbial count, fruit number, cumulative yield, fruit quality traits as compared to non-solarized (natural) conditions. Root soil ratio of resident microbes at 15 cm depth was also worked out in the rhizosphere zone and non-rhizosphere zone. The data suggested an increased rhizosphere acid- and alkaline phosphate and dehydrogenase enzyme activity can be used as a good indicator of phosphorus nutrition in solarized organic soils compared to non-solarized (natural) soils. The results suggested that PGPR inoculations could alleviate the deleterious effects of soil borne microbial population on the phenological and pomological attributes of strawberry plants under organic growing solarized soils. Root inoculation with PGPR probiotics significantly affected leaf nutrient concentration in terms of DOP and ΣDOP indexes which showed an increase in N, P, K and Mg concentration in the leaves in solarized plots compared to natural plots. Principal component analysis induced the differences at various PGPR probiotics applied has identified maximum of the total variance based on the Eigen value (>1) and explained 65.38% (PC1), 79.68% (PC2), 88.05% (PC3) and 92.67% (PC4) of the cumulative variance. PC4 accounted for highest total cumulative variances among fruit phenological, morphometric and generative potential strawberry traits. The study indicated PGPR probiotics coupled with soil solarization as a promising technology to maintain healthy rhizosphere, and as an alternative to chemicalised farming of strawberry to enhance quality production in calcareous soils of Shiwalik foothills of north-west Himalayas.

Antarctic tundra soil metagenome as useful natural resources of cold-active lignocelluolytic enzymes.

Lignocellulose composed of complex carbohydrates and aromatic heteropolymers is one of the principal materials for the production of renewable biofuels. Lignocellulose-degrading genes from cold-adapted bacteria have a potential to increase the productivity of biological treatment of lignocellulose biomass by providing a broad range of treatment temperatures. Antarctic soil metagenomes allow to access novel genes encoding for the cold-active lignocellulose-degrading enzymes, for biotechnological and industrial applications. Here, we investigated the metagenome targeting cold-adapted microbes in Antarctic organic matter-rich soil (KS 2-1) to mine lignolytic and celluloytic enzymes by performing single molecule, real-time metagenomic (SMRT) sequencing. In the assembled Antarctic metagenomic contigs with relative long reads, we found that 162 (1.42%) of total 11,436 genes were annotated as carbohydrate-active enzymes (CAZy). Actinobacteria, the dominant phylum in this soil's metagenome, possessed most of candidates of lignocellulose catabolic genes like glycoside hydrolase families (GH13, GH26, and GH5) and auxiliary activity families (AA7 and AA3). The predicted lignocellulose degradation pathways in Antarctic soil metagenome showed synergistic role of various CAZyme harboring bacterial genera including Streptomyces, Streptosporangium, and Amycolatopsis. From phylogenetic relationships with cellular and environmental enzymes, several genes having potential for participating in overall lignocellulose degradation were also found. The results indicated the presence of lignocellulose-degrading bacteria in Antarctic tundra soil and the potential benefits of the lignocelluolytic enzymes as candidates for cold-active enzymes which will be used for the future biofuel-production industry.

Thermal oxidation of carbon in organic matter rich volcanic soils: insights into SOC age differentiation and mineral stabilization

Radiocarbon ages and thermal stability measurements can be used to estimate the stability of soil organic carbon (OC). Soil OC is a complex reservoir that contains a range of compounds with different sources, reactivities, and residence times. This heterogeneity can shift bulk radiocarbon values and impact assessment of OC stability and turnover in soils. Four soil horizons (Oa, Bhs, Bs, Bg) were sampled from highly weathered 350 ka Pololu basaltic volcanics on the Island of Hawaii and analyzed by Ramped PyrOX (RPO) in both the pyrolysis (PY) and oxidation (OX) modes to separate a complex mixture of OC into thermally defined fractions. Fractions were characterized for carbon stable isotope and radiocarbon composition. PY and OX modes yielded similar results. Bulk radiocarbon measurements were modern in the Oa horizon (Fm = 1.013) and got progressively older with depth: the Bg horizon had an Fm value of 0.73. Activation energy distributions (p(E)) calculated using the ‘rampedpyrox’ model yielded consistent mean E values of 140 kJ mol−1 below the Oa horizon. The ‘rampedpyrox’ model outputs showed a mostly bimodal distribution in the p(E) below the Oa, with a primary peak at 135 kJ mol−1 and a secondary peak at 148 kJ mol−1, while the Oa was dominated by a single, higher E peak at 157 kJ mol−1. We suggest that mineral-carbon interaction, either through mineral surface-OC or metal-OC interactions, is the stabilization mechanism contributing to the observed mean E of 140 kJ mol−1 below the Oa horizon. In the Oa horizon, within individual RPO analyses, radiocarbon ages in the individual thermal fractions were indistinguishable (p > 0.1). The flat age distributions indicate there is no relationship between age and thermal stability (E) in the upper horizon (> 25 cm). Deeper in the soil profile higher µEf values were associated with older radiocarbon ages, with slopes progressively steepening with depth. In the deepest (Bg) horizon, there was the largest, yet modest change in Fm of 0.06 (626 radiocarbon years), indicating that older OC is slightly more thermally stable.

Reduced catalytic activity of an exogenous extracellular β-D-glucosidase due to adsorption on a model humic-clay complex and different soils under wetting and drying cycles

To ascertain the role of extracellular enzymes in soil biochemical reactions, we followed the changes in catalytic activity of an exogenous β-glucosidase (GLU) enzyme after its adsorption on a synthetic model humic-clay complex, composed by a lignite humic acid coupled by Al bridges to a Ca-montmorillonite (HM), and on three sterilised soils (DS, ISC and IST) with different properties. Either HM or the selected soils enabled a stable GLU adsorption that induced a significant decrease of GLU activity. In the case of soils, both the largest GLU adsorption and reduction of catalytic activity was observed for the clayey and organic matter-rich ISC soil. When the GLU-soil adducts were subjected to wetting and drying (W/D) cycles for 3 and 6 weeks, the enzyme activity was further largely reduced after the first 3 weeks of W/D, while the decrease progressed more slowly during the following 3 weeks. This was attributed to the increasing modification of the enzyme conformational structure due to formation of dispersive and hydrogen bonds with the inorganic and organic components of HM and soils. Our results showed that an exogenous extracellular enzyme, such as GLU, is quantitatively immobilised on model and real soil aggregates, and that the catalytic activity is significantly and progressively reduced by soil physical-chemical changes, thereby implying that soil biochemical transformations are to be accounted more to intracellular than extracellular enzymes.

Enhancement of cadmium adsorption by EPS-montmorillonite composites

Extracellular polymeric substance (EPS)-mineral associations occur naturally in soil and sediments, and they might play crucial roles in heavy metals immobilization. In this study, EPS-montmorillonite composites with different weight ratios were characterized and investigated for their Cd(II) sorption behavior. The results showed that the EPS chains can intercalate into montmorillonite layers by hydrogen bonding connection and chemical reaction between CO, C–N and COO− groups with interlayer cations of montmorillonite, therefore promoting delamination of montmorillonite, especially under a lower weight ratio. An enhancement adsorption of heavy metals was obtained with the composites at lower weight ratios of 1:50 and 0.5:50, whereas composites with higher weight ratio of 5:50 presented a reduced adsorption ability, demonstrating that adsorption of Cd(II) onto the EPS-montmorillonite composites was weight ratio dependent. AFM, CLSM, FT-IR and XPS analysis illustrated that the enhancement of sorption under low weight ratio can be attributed to the release of surface active sites of EPS because of reduced aggregation, the increase of negative surface charges when EPS and montmorillonite were interacted and additional bridging of cadmium ions between EPS and montmorillonite. These findings extend the knowledge into the mobility and fate of Cd(II) in organic matter rich soils and sediments.

Enhanced Recovery of Nonextractable Benzo[a]pyrene Residues in Contrasting Soils Using Exhaustive Methanolic and Nonmethanolic Alkaline Treatments

The fate, impacts, and significance of polycyclic aromatic hydrocarbon (PAH) nonextractable residues (NERs) in soils remain largely unexplored in risk-based contaminated land management. In this study, seven different methanolic and nonmethanolic alkaline treatments, and the conventional methanolic saponification, were used to extract benzo[ a]pyrene (B[ a]P) NERs that had been aged for 180 d from four contrasting soils. Up to 16% and 55% of the amount of B[ a]P spiked (50 mg/kg) into soils was nonextractable after 2 d and 180 of aging, respectively, indicating rapid and progressive B[ a]P sequestration in soils over time. The recovery of B[ a]P from soils after 180 d of aging was increased by up to 48% by the seven different alkaline extractions, although the extraction efficiencies of the different alkaline treatments did not differ significantly ( p > 0.05). Approximately 40% of B[ a]P NERs in the sandy-clay-loam organic matter-rich soil was recovered by the exhaustive alkaline extractions after 180 d of aging, compared to only 10% using conventional methanolic saponification. However, the amounts of B[ a]P NERs recovered depend on soil properties and the amounts of NERs in soils. A significant correlation ( R2 = 0.69, p < 0.001) was also observed between the amounts of B[ a]P recovered by each of the seven alkaline extractions in the contrasting soils and corresponding NERs at 180 d of aging, indicating a potential association warranting further investigations. Extraction techniques that estimate the amounts of PAH NERs recoverable in soil can help give a better understanding of the fate of NERs in soil.

Trace metal mobilization by organic soil amendments: insights gained from analyses of solid and solution phase complexation of cadmium, nickel and zinc

The accumulation of Cd in soils worldwide has increased the demand for methods to reduce the metal's plant bioavailability. Organic matter rich soil amendments have been shown to be effective in achieving this. However, it is not known how long these amendments can retain the Cd, and whether dissolved organic matter (DOM) released from them can enhance the metal's mobility in the environment. In this study we sought to test the Cd binding capacity of various organic soil amendments, and evaluate differences in characteristics of the DOM released to see if they can explain the lability of the Cd-DOM complexes. We collected ten organic soil amendments from around New Zealand: five different composts, biosolids from two sources, two types of peat and spent coffee grounds. We characterised the amendments' elemental composition and their ability to bind the Cd. We then selected two composts and two peats for further tests, where we measured the sorption of Ni or Zn by the amendments. We analysed the quality of the extracted DOM from the four amendments using 3D Excitation Emission Matrix analysis, and tested the lability of the metal-DOM complexes using an adapted diffusive gradients in thin-films (DGT) method. We found that composts bound the most Cd and that the emergent Cd-DOM complexes were less labile than those from the peats. Ni-DOM complexes were the least labile. The aromaticity of the extracted DOM appears to be an important factor in determining the lability of Ni complexes, but less so for Zn and Cd.

Matching Estonian humus cover types’ (pro humus forms’) and soils’ classifications

For characterization of soil cover influence on formation and functioning of ecosystems, the special attention should be paid to its biologically active superficial part i.e. to the humus cover (HC). The used by us term ‘HC type’ corresponds well to the internationally recognized term ‘humus form’. The fabric of the HC is characterized by the humus profile, which consists of the organic matter-rich soil horizons (forest floor, humus, organo-mineral and peat horizons). For the basis of comparative analysis, the classification schemas, elaborated separately for natural area HCs and soils, were used. In both schemas, the classification units are arranged according to soils moisture conditions and genesis. A good coincidence of HCs’ and soils’ types was obtained in relation to moisture scalar. The four first stages of moisture conditions enfold soils, in which the leading role belongs to the mineral components of the soil. The fifth column enfolds the transitional HC types between mineral and peat soils, whereas the typical peat soils are located in the 6th column. The genetic-lithic scalar shows that the calci-mull HCs have formed on soils rich in free calcium carbonate; forest-mull on calcareous pebble and leached soils; moder-mull on slightly eluviated endocalcareoussoils; moder types - on glossic and sod-podzolic soils; moder-mor on transitional podzols (between sod-podzolic and typical podzols) and mor type HCs on typical podzols. HCs in the 1st column (drought-timid soils) are divided according to their calcareousness and acidity, but those in the 5th and 6th columns (peaty and peat soils) - according to the content of nutrition elements in the feeding water, into 3 types. The matching of classification units of HCs and soils are analysed as well on the basis of the soils matrix table.