Search Results (247)

The biogenic organization of widespread valley pine ecosystems on sandy alluvium leads to an increase in soil fertility, productivity, and biodiversity through autogenic successions. Using our own stationary observations and literary data on the productivity of pine forests in Russia, Belarus, and Ukraine, we quantified the mechanism of autogenic forest successions associated with carbon sequestration and the influence of organic matter dynamics on the fertility and water retention of sandy soils. The low rate of organic matter turnover in primary succession leads to the intensive accumulation of thick (6–8 cm) forest litter and the formation of small humus-eluvial horizons with total carbon storage up to 50 Mg/ha. This soil structure retains 2–6 times more water and biophilic elements than in the original sandy alluvium. It is suitable for the settlement of more demanding broadleaf species and nemoral herbs with higher rates of litterfall, its decomposition and humification. As a result, simple pine forests on Arenosols and primitive Sod-podzolic soils are replaced by complex, more productive linden–oak–pine ecosystems on developed Cambisols with thick (up to 30 cm) humus horizons, carbon storage of 80–100 Mg/ha and higher (2–7 times compared to the previous soils) fertility and water-holding capacity. This mechanism is adequately described by a nonlinear process model with a trigger reaction of plant productivity to the storage and quality of soil organic matter, suitable for predicting long-term carbon sequestration during the succession of valley pine forests and the effectiveness of artificial afforestation. Full article

With the frequent occurrence of global droughts, modified biochar has demonstrated the potential to be an efficient soil amendment, which could affect carbon and nitrogen sequestration in arid soil. Therefore, this study investigated the co-application of pristine biochar (BC), Fe-modified biochar (FB) and H₂O₂-modified biochar (HB) with green manure during a 70-day laboratory incubation under drought conditions and normal moisture conditions. The emissions were quantified using gas chromatography, while microbial necromass carbon and nitrogen were measured by quantifying the amino sugar content by gas chromatography–mass spectrometry, and other soil carbon and nitrogen fractions were determined through chemical analysis. The results revealed that under drought conditions, compared to BC co-application with green manure, the total carbon loss of FB and HB co-application with green manure was reduced from 24.38% to 13.14% and 14.27%, respectively, and the total nitrogen loss was also reduced from 14.61% to 7.23% and 7.27%, respectively. This reduction occurred because FB and HB protected soil organic matter through iron oxide binding and micropore adsorption, thereby increasing the content of soil total humus acid (>5%) and microbial necromass nitrogen (>16%). In addition, under normal moisture conditions, BC, FB and HB co-application with green manure enhanced microbial activity and promoted the formation of stable total humus acid, thereby enhancing carbon and nitrogen sequestration. In conclusion, this study provides crucial theoretical support for the optimization of the green manure return via modified biochar co-application in arid environments. Full article

Long-term cultivation practices, in which mineral fertilizers are the only amendments made to crop-supporting soils, are giving rise to the degradation of soil structures in the world’s most fertile soils. This leads to erosion and to the loss of productivity and may well become a greater threat than that of global warming. Humic substances (structurally related compounds), and humin (which no longer falls within the modern definitions of humic substances), are major transformation or humification components of organic matter entering the soil, with varying resistance to biological degradation, and properties vastly contributing to soil fertility. There is considerable discussion on the macromolecular structures arising from associations or supramolecular structuring of some components of humic substances. The compositions, structures, shapes, sizes, and surface properties of these molecular components determine their intra- and inter-molecular associations, their interactions with the soil particles, and particularly with the soil inorganic colloids. Such interactions play a vital role in soil aggregates’ formation, which is important for soil health and productivity. In this work, an outline is given of modern methods for the isolation of broadly defined soil organic components, of what is known of their origins (plant or microbial), compositions, sizes and shapes, of how they interact to promote soil structure and productivity, and how the materials composing the hydrophobic fraction form strong associations with the inorganic colloids. A better understanding should be sought of how these interactions and associations take place giving rise to the structured systems that are characteristic of fertile soils. Full article

Most lacustrine dissolved organic matter (DOM) still lacks comprehensive environmental sources and molecular characterization, especially in plateau lakes. Herein, macrophytes and algae from contrasting lakes of the Yunnan-Guizhou Plateau, together with Suwannee River fulvic acid (SRFA), were used to characterize the total identified DOM (Bulk-DOM) and low-molecular-weight DOM (LMW-DOM, <200 Da). To address this, we combined spectroscopy with Fourier transform ion cyclotron resonance (FT-ICR) and Orbitrap mass spectrometry (MS). Algae-derived DOM (ADOM) exhibited endogenous DOM characteristics, while macrophyte-derived DOM (MDOM) showed the characteristics of endogenous and terrigenous DOM. ADOM contained numerous heteroatoms, with high proportions of proteins, carbohydrates, and lipids. The chemical structures of ADOM were more aliphatic and degradable than that of MDOM. Conversely, MDOM and SRFA had higher degree of humification and aromaticity and showed greater resistance to microbial degradation. The capability of Orbitrap MS to characterize P-containing molecules was superior to FT-ICR MS. Moreover, significant differences were found between FT-ICR and Orbitrap MS in weighted average carbon atom number, weighted average mass-to-charge ratio, carbohydrates, and P-containing compounds. LMW-DOM accounted for approximately 10% of Bulk-DOM. Compared to Bulk-DOM, LMW-DOM was more active than Bulk-DOM because of the reduced state and more N-containing compounds. This study provides a valuable perspective to reveal the molecular characteristics and behaviors of ADOM and MDOM, which has crucial implications for carbon cycling in aquatic ecosystems. Full article

The anaerobic co-digestion of agricultural residues emerges as a promising strategy for energy recovery and nutrient recycling within circular agricultural systems. This study aimed to optimize co-digestion parameters for vinegar residue (VR) and cattle manure (CM) using an orthogonal experimental design. Three key variables were investigated which are the co-substrate ratio (VR to CM), feedstock-to-inoculum (F/I) ratio, and total solids (TS) content. Nine experimental combinations were tested to evaluate methane yield, feedstock degradation, and digestate characteristics. Results showed that the optimal condition for methane yield comprised a 2:3 co-substrate ratio, 1:2 F/I ratio, and 20% TS, achieving the highest methane yield of 267.84 mL/g volatile solids (VS) and a vs. degradation rate of 58.65%. Digestate analysis indicated this condition generated the most nutrient-rich liquid digestate and solid digestate, featuring elevated N, P, and K concentrations, acceptable seed germination indices (GI), and moderate humification levels. While total nutrient content did not meet commercial organic fertilizer standards, the digestate is suitable for direct land application in rural settings. This study underscores the need to balance energy recovery and fertilizer quality in anaerobic co-digestion systems, providing practical guidance for decentralized biogas plants seeking to integrate waste treatment with agricultural productivity. Full article

This study aimed to develop an effective method to overcome the challenge of straw return in cold-region soil. We systematically investigated the synergistic mechanism of montmorillonite (MMT) and composite amino acid (CAA) on straw humification and carbon sequestration through a low-temperature litterbag field experiment. The results indicate that the combined treatment (MMT-CAA) significantly increased the decomposition rate of straw by 42.1% compared to the control (CK), with MMT showing particular efficacy in lignin degradation (28.3% reduction), while the CAA preferentially decomposed cellulose (19.7% reduction). An FTIR analysis of the decomposition products confirmed these findings. Water-soluble organic carbon (WEOC) and its three-dimensional fluorescence spectra exhibited a 25.0% increase in MMT-CAA and enhanced aromaticity of humic acid-like substances. Humic substances and their ¹³C-NMR revealed that MMT-CAA enhanced humic acid formation and molecular stability by 31.4% (with a 47.8% increase in aromaticity). A further redundancy analysis and symbiotic network of microorganisms demonstrated that MMT-CAA increased the abundance of lignocellulose-degrading phyla (Actinomycetes and Stramenomycetes) and the formation of a complex co-degradation network. Field corn planting trials indicated that MMT-CAA increased plant height by 55.1%, stem thickness by 58.7%, leaf area by 70.2%, and the SPAD value by 41.1%. Additionally, MMT significantly reduced CO₂ and N₂O emission fluxes by 35.6% and 15.8%, respectively, while MMT-CAA increased CH₄ uptake fluxes by 13.4%. This study presents an innovative strategy, providing mechanistic insights and practical solutions to synergistically address the challenges of slow straw decomposition and carbon loss in cold regions. Full article

The degradation of modern and ancient permafrost-affected soils and organic-rich sediments and the release of relict soil organic matter from the frozen state are critical for understanding the global carbon cycle in a changing climate. The molecular structure of humic acids isolated from modern Cryosols and paleosoils from the Ice Complex deposits in the Batagay megaslump area was investigated. The elemental composition analysis was performed using a CHN analyzer, and molecular composition analysis was determined by CP/MAS ¹³C-NMR spectroscopy. Analysis of the molecular structure of humic acids showed that MIS 5e paleosoils are characterized by a relatively high content of aliphatic structural fragments (C,H-AL—29–36%) and a low content of aromatic structural fragments (AR/AL—0.49–0.43), which reveals low humification rates in this time period. The composition of humic acids from MIS 7 paleosoils shows a relatively high content of aromatic structural fragments compared to modern soils (AR/AL—0.47) and MIS 5e deposits (AR/AL—0.67–0.54), indicating a longer humification process in heterogenic conditions (warm and cold periods). The results indicate that the molecular structure of humic acids is a dynamic parameter of the environment that reflects the local conditions of pedogenesis and organic matter formation. Permafrost thawing leads to the release of organic matter (including matter that is relatively weakly resistant to biodegradation where aliphatic structural fragments dominate the composition of humic acids) that may strengthen the emission of climate-active gases into the atmosphere and boost climate change. Full article

This study innovatively integrates ball-milled manganese dioxide nanozyme (MDMP) with the Streptomyces rochei ZY-2 inoculant in aerobic rice straw composting. The ZY-2 inoculant efficiently degrades the three major components to generate humus precursors such as phenols and quinones, while the MnO₂ nanozyme accelerates precursor polymerization into stable humic acid (HA) via oxygen vacancy-mediated catalytic activity. Simultaneously, this combination regulates microbial communities to reduce greenhouse gas emissions. The results show that the co-treatment group (ZY-2+ MnO₂ nanozyme) had an increased HA content by 30.8%, raised HA/FA ratio by 31.6%, and degradation rates of 30.75%, 31.39%, and 16.74% for cellulose, hemicellulose, and lignin, respectively. Additionally, cumulative emissions of CH₄, N₂O, and NH₃ were significantly reduced by 35.22%, 28.23%, and 25.67% compared to the control, attributed to the MnO₂ nanozyme’s inhibition of methanogens, enhanced nitrogen fixation, and ZY-2-driven microbial metabolic optimization. This study proposes a dual-effect strategy of “enhanced humification-synergistic greenhouse gas mitigation” for agricultural waste recycling, demonstrating significant practical value. Full article

The EU’s Circular Economy Action Plan promotes the use of organic waste as fertilizer, thus allowing the recycling of nutrients in the agricultural system. Research on the agronomic reuse of composted substrates previously employed for mushroom cultivation remains limited, despite their rich content of plant residues and fungal biomass, which could be repurposed as soil amendments under suitable conditions. This study evaluated the agronomic potential of spent mushroom substrates from Agaricus bisporus and Pleurotus ostreatus, including recomposted A. bisporus residues. A range of analytical procedures was employed to assess their suitability for soil improvement and the formation of humic-like substances, including physical, chemical, microbiological, phytotoxicity, and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) analyses. The spent Pleurotus substrate exhibited low nutrient content (1.1% N, negligible P, 0.9% K), but high water retention (820 kg water Mg⁻¹) and 48% organic carbon (OC), indicating its potential as a soil amendment or seedling substrate. In contrast, spent and composted Agaricus substrates showed moderate nutrient content (1.8–2.7% N; 0.8–0.7% P and 1.3–1.8% K), appropriate C/N ratios (10–15), and sufficient OC levels (24–30%), supporting their use as fertilizers. However, elevated salinity levels (18–23 dS m⁻¹) may restrict their application for salt-sensitive crops. No significant phytotoxic effects on seed germination were observed, and microbiological analyses confirmed the absence of Salmonella spp. in the three substrates. Py-GC/MS revealed a humic acid-like fraction comprising altered lignin structures enriched with lipid and nitrogen compounds. Overall, the studied materials demonstrate promising agronomic value and the capacity to contribute to long-term soil carbon storage. Full article

This study aimed to evaluate the impact of vineyard cultivation time and the use of metal-based fungicides on the chemical fractions of soil organic matter (SOM) as well as their interactions with Cu, Zn, and Mn in vineyard soils from Southern Brazil with varying histories of fungicide application. Soil samples were collected in 2017 from vineyards aged 35, 37, and 39 years in the Serra Gaúcha region and 13, 19, and 36 years in the Campanha Gaúcha. In each region, samples were also collected from a non-anthropized reference area. In the oldest vineyards, sampling was conducted both within and between the rows of planting. Chemical fractionation of SOM was performed: non-humic substances (nHSs), particulate organic matter (POM), fulvic acid (FA), humic acid (HA), and humin (Hu). Fourier-transform infrared (FTIR) spectra were obtained for the HA, from which the aromaticity index (AI) and relative intensities (RIs) were calculated. In each SOM fraction, total organic carbon and the concentrations of Cu, Zn, and Mn were determined. Changes in land use alter the forms and distribution of soil organic carbon (SOC) and, consequently, of metals. Elemental and spectroscopic analyses of HS revealed that HA in the reference areas (forest and native grassland) was more aliphatic and had higher concentrations of polysaccharides, indicating fractions with a lower degree of stabilization. However, in vineyard areas, HA exhibited greater humification and aromaticity. Increasing cultivation time gradually increased soil carbon content, indicating that viticultural agroecosystems can sequester carbon in the soil over time, reaching levels similar to those observed in the reference areas. When comparing vineyard areas alone, with row collections and inter-row collections, we observed an increase in SOC levels in areas managed with cover crops, demonstrating the importance of conservation management in these areas. When evaluating the distribution of metals in these soils, we could observe the high affinity of Cu for the functional groups of SOM, with FA and HA responsible for the complexation of these elements in the soil. For Zn and Mn, the greatest accumulations were observed in the Hu fraction due to their greater affinity for soil clay minerals. This shows that soil organic matter is a key component in the complexation of metals in soils, reducing their availability and potential toxicity to cultivated plants. Full article

This study investigates the composition and transformation of soil organic matter (SOM) across seven sites in Maritime Antarctica, focusing on the impact of bird activity and vegetation cover on SOM dynamics. There is limited knowledge of the stability of Antarctic SOM and the effects of seabird colonies on it. This study aims to address the knowledge gap regarding drivers of soil organic matter transformations in polar ecosystems. Hot water-extractable carbon (HWC) and carbon extracted with phosphoric acid (PHP-C) were chosen as parameters for the labile carbon pool. A stable carbon pool was here characterized as one with alkali-soluble organic compounds opposing microbial decomposition. This carbon pool has long (decades) turnover rates, and therefore is regarded stable. The mentioned carbon pools were used to calculate humification indices. The HWC in studied soils ranged from 1.5 to 4.3% of total carbon, while the PHP-C varied largely and was not correlated with HWC. Soils influenced by current or historical bird colonies (particularly penguins and skuas) exhibited elevated labile carbon fractions, indicating active microbial processing. In contrast, sites without bird influence showed lower biological activity. The stable carbon peaked at 18.9% of total carbon, indicating distinct soil transformation stages. The humification degree (HD) and labile-to-stable carbon (L/S) ratio were used to assess SOM stability, revealing that former bird rookeries had the most stabilized SOM, while recently deglaciated sites were in early stages of organic matter accumulation. Vegetation cover, though secondary to bird impact, was positively correlated with SOM humification, supporting the role of vascular plant-derived organic input in carbon stabilization. The study showed a clear link between bird activity and SOM dynamics, supporting the concept of biological legacies in soil formation in Antarctica. It highlighted the role of vegetation in SOM stabilization, which is crucial for understanding how terrestrial ecosystems may evolve as ice retreats and plant colonization expands. Full article

This study investigated the impacts of land-use history and an episodic flood event on the soil quality of a riverine floodplain ecosystem, providing long-term and short-term disturbance perspectives. The study took place in the Saint Michael’s College Natural Area, which has over a hundred-year history of land-use change. Based on aerial orthoimagery, three zones (a recently abandoned farm field, a new-growth forest, and an old-growth forest) were selected that reflected different land-use histories. Two plots were selected per zone and pooled soil samples were collected from each before and after a major flooding event. Surface soil quality before flooding was often similar among the new- and old-growth forested areas (1.4 mg-P/g-soil, 6.8% soil organic matter (SOM), 0.79 humification index (HIX), and 13% Peak T) but differed from that found in the recently abandoned farm field, which had higher phosphorus levels (1.6 mg-P/g-soil), lower SOM content (3.9%), more microbial-like SOM (0.65 HIX and 17% Peak T), and drier soils. Flooding caused SOM to better resemble that of a forest rather than an agricultural field, and it lowered phosphorus levels. The results of our study suggest that episodic flooding events could help accelerate the restoration of soil organic matter conditions. Full article

Micro/nanoplastics (MNP) and endotoxin, typical emerging contaminants, can be found in marine aqueous systems due to various natural and anthropogenic activities, and their co-occurrence may influence the biophysicochemical characteristics of seawater. Moreover, endotoxins may be transported by the micro/nanoplastics or increase the deformation of these substances, comprising other risks to the ecosystem. However, the impacts of the co-occurrence of micro/nanoplastics and endotoxins in seawater remain unknown. We studied the effects of endotoxin at three concentration levels in seawater and its combined impact with micro/nanoplastics at three doses on biophysicochemical processes in seawater through spectroscopic analysis, leaching indicators (turbidity and humidification index), oxidative potential, antioxidant activity, and biofilm production. The results showed that the UV–VIS spectra of seawater changed with their co-occurrence. The co-presence of MNPs and endotoxins increased the turbidity in seawater, indicating the leaching of micro/nanoplastic in the presence of endotoxins. A higher humification index in seawater showed the formation of dissolved organic substances in micro/nanoplastic and endotoxin seawater compared to the results for untreated seawater. Dithioerythritol assay revealed the differences in oxidative potentials of plain seawater and seawater in the co-presence of micro/nanoplastics and endotoxins. An important biochemical reaction in seawater was tested using biofilm formation. The results showed higher biofilm formation in their co-presence. This study provides new insights into the effects of micro/nanoplastics and their composite pollution with endotoxins on biophysiochemical indicators in seawater. Full article

This article presents a review of several non-exclusive pathways for the sequestration of soil organic carbon, which can be classified into two large classical groups: the modification of plant and microbial macromolecules and the abiotic and microbial neoformation of humic substances. Classical studies have established a causal relationship between aromatic structures and the stability of soil humus (traditional hypotheses regarding lignin and aromatic microbial metabolites as primary precursors for soil organic matter). However, further evidence has emerged that underscores the significance of humification mechanisms based solely on aliphatics. The precursors may be carbohydrates, which may be transformed by the effects of fire or catalytic dehydration reactions in soil. Furthermore, humic-type structures may be formed through the condensation of unsaturated fatty acids or the alteration of aliphatic biomacromolecules, such as cutins, suberins, and non-hydrolysable plant polyesters. In addition to the intrinsic value of understanding the potential for carbon sequestration in diverse soil types, biogeochemical models of the carbon cycle necessitate the assessment of the total quantity, nature, provenance, and resilience of the sequestered organic matter. This emphasises the necessity of applying specific techniques to gain insights into their molecular structures. The application of appropriate analytical techniques to soil organic matter, including sequential chemolysis or thermal degradation combined with isotopic analysis and high-resolution mass spectrometry, derivative spectroscopy (visible and infrared), or ¹³C magnetic resonance after selective degradation, enables the simultaneous assessment of the concurrent biophysicochemical stabilisation mechanisms of C in soils. Full article

The purpose of this research was to determine the properties of humic acids isolated from soil samples taken from a 40-year static experiment—the experimental factors were fertilization with manure (30 t ha⁻¹; FYM) and nitrogen at rates of 40, 60 and 120 t ha⁻¹. From the soil samples (Luvisol), humic acids (HAs) were extracted and the following were determined: elemental composition, hydrophilic and hydrophobic properties and spectrometric properties in the UV–VIS and IR range. The HAs of the soil fertilized with manure and N compared to the HAs of the soil fertilized with N (without manure) were characterized by a higher degree of aliphaticity and, consequently, a higher share of hydrophilic fractions and lower values of internal oxidation. Based on the spectrometric parameters, it was indicated that the HA particles of the manure-fertilized soil are characterized by a higher share of undecomposed lignin fragments, a lower degree of humification and at the same time, a higher susceptibility to oxidation. The obtained relationships showed that the aromaticity and hydrophobicity of the HA molecules of the manure-fertilized soil can be increased at certain N doses (60 and 120 t ha⁻¹), which is particularly important in terms of the role that humic substances play in carbon sequestration. Full article