Soil Organic Matter Components Research Articles

Assessment of the capability of Landsat-8 satellite imagery for predicting soil organic carbon distribution

Soil organic carbon (SOC) is an important component of soil and plays a crucial role in addressing climate change. As a key component of soil organic matter, SOC directly impacts soil fertility, water retention, nutrient cycling, and overall soil health. The determination of SOC concentrations in soil often relies on costly physical sampling and chemical analysis. The aim of this research was to build a predictive model of SOC using satellite imagery of Landsat 8 OLI/TIRS over an agricultural area (Oued El Alleug) in the north of Algeria. The statistical correlations between the spectral bands (B2 and B6) and chemically measured SOC concentrations showed that it is possible to predict spatially the SOC concentrations. The results also showed that the topographic variables are not determinant in the spatial prediction of SOC concentrations. The predicted model showed an acceptable performance with a coefficient of determination (R2) = 0.7 and a root mean square error (RMSE) = 7.08 g/kg during the validation phase. The results of this study are important, as they will facilitate decision-making in soil conservation practices and enhance land management, especially in areas facing increasing agricultural and environmental pressures.

Divergent response of Chernozem organic matter towards short-term water stress in Poa pratensis L. rhizosphere and bulk soil in pot experiments: A spectroscopic study

Understanding and controlling rhizospheric processes under abiotic stress is one of the key challenges in addressing food security amid the climate crisis. In this work, the impact of short-term drought and overwatering on soil organic matter (SOM) of Haplic Chernozem in the rhizosphere of Poa pratensis L. and in bulk soil was investigated. The vegetation experiment was conducted in a climatic chamber at soil moisture levels of 35, 80, and 200 % of the field capacity. UV-Vis and spectrofluorometry were used to describe the water-extractable organic matter (WEOM) characteristics and fluorofores signature, and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to describe functional group composition of SOM. Composition and properties of SOM and WEOM of Chernozem significantly change after exposure to short-term water stress. Drought does not affect the composition of rhizosphere SOM except increasing the proportion of polysaccharides, but leads to the decrease in aromaticity and increase in molecular weight of humic-like components of rhizosphere WEOM. These findings reflect Poa adaptation to water deficiency and microbial activity suppression which results in accumulation of SOM intermediate decomposition products. On the contrary, bulk WEOM wasn't affected by drought but SOM became enriched with aromatic and oxidised components. Overwatering leads to equalisation of bulk and rhizospheric SOM composition due to a decrease in the proportion of aromatic and carboxylic components of bulk SOM and the accumulation of microbial products in both bulk and rhizospheric SOM. In general, rhizospheric WEOM undergoes relatively significant changes relative to the optimum water regime under moisture deficit, and bulk WEOM — under overwatering. The findings illustrate the involvement of the both WEOM and SOM in maintaining resilience of the soil-plant system as well as the difference in watering conditions impact on SOM in rhizosphere and bulk soil. SOM spectral data can be used for assessing the state of soil systems, such as changes in microbial activity and adaptation of the soil-plant system to abiotic stress. Our findings also illustrate the differences in the organic matter transformation of the Poa pratensis rhizosphere and the bulk Chernozem depending on environmental factors.

Influences of wildfire on the soil dissolved organic matter characteristics and its electron-donating capacity

Global increases in the intensity and frequency of wildfires are driving major changes in soil organic matter (SOM) characteristics, including soil dissolved organic matter (DOM). As the most crucial component of SOM, soil DOM plays a pivotal role in the carbon cycle and regulates the environmental fate of contaminants through its versatile reactivities, including electron-donating capacity (EDC). However, it is still being determined how wildfire influences key characteristics of soil DOM and subsequent effects on EDC in forest soils. Thus, we conducted our study to fill this gap with the forest soils of Jinyun Mountain Nature Reserve of China, which experienced an unprecedented wildfire event in 2022. The results from optical characterization, high-performance size-exclusion chromatography (HPSEC), and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) showed decreasing molecular weight but elevating nitrogen-containing molecular formulas of soil DOM in the burned soils. This could be attributed to the Maillard reaction and microbial re-colonies. Additionally, wildfires increased the condensed aromatics and lignin components in soil DOM. In the burned soils, we observed increasing EDC of soil DOM, which accounts for an increase in lignin-derived phenolic components. Overall, the findings of this study demonstrate that eco-disturbances, such as wildfires, induce alterations in the properties of DOM, leading to variations in its reactivity and potentially influencing the fate of environmental pollutants beyond carbon dynamics alone. Thus, incorporating the dynamic properties of soil DOM, particularly in the context of climate change, can enhance the assessment of risks associated with contaminants in soil and water, providing valuable insights.

Variations in source-specific soil organic matter components across 32 forest sites in China

Forest soils store substantial amounts of carbon in various soil organic matter (SOM) components due to high plant litter inputs and active microbial turnover. However, the variations in plant- and microbial-derived SOM components in surface and subsurface forest soils across a wide geographic scale remain poorly understood. This study investigated the SOM components from aboveground and belowground plant inputs and fungal and bacterial necromass in surface (soil0–5 cm) and subsurface (soil5–10 cm) soils across 32 forest sites in China and analyzed their relationships with climate and edaphic factors. Compared to soil0–5 cm, soil5–10 cm exhibited lower soil organic carbon content and cutin biomarker concentration but higher concentrations of fungal necromass carbon and lignin phenols. Higher mean annual precipitation led to higher concentrations of cutin and suberin biomarkers in soil0–5 cm and soil5–10 cm, respectively. Higher soil organic carbon content was associated with lower plant-derived lignin biomarkers, higher lignin oxidation degrees, and increased microbial necromass-derived amino sugars across sites, highlighting the pivotal role of microbial necromass in SOM stabilization. Additionally, both fungal and bacterial necromass decreased with increasing mineral weathering across sites. These insights improve the understanding of environmental drivers of source-specific carbon storage in forest soils.Graphical

Spatial Prediction of Organic Matter Quality in German Agricultural Topsoils

Soil organic matter (SOM) and the ratio of soil organic carbon to total nitrogen (C/N ratio) are fundamental to the ecosystem services provided by soils. Therefore, understanding the spatial distribution and relationships between the SOM components mineral-associated organic matter (MAOM), particulate organic matter (POM), and C/N ratio is crucial. Three ensemble machine learning models were trained to obtain spatial predictions of the C/N ratio, MAOM, and POM in German agricultural topsoil (0–10 cm). Parameter optimization and model evaluation were performed using nested cross-validation. Additionally, a modification to the regressor chain was applied to capture and interpret the interactions among the C/N ratio, MAOM, and POM. The ensemble models yielded mean absolute percent errors (MAPEs) of 8.2% for the C/N ratio, 14.8% for MAOM, and 28.6% for POM. Soil type, pedo-climatic region, hydrological unit, and soilscapes were found to explain 75% of the variance in MAOM and POM, and 50% in the C/N ratio. The modified regressor chain indicated a nonlinear relationship between the C/N ratio and SOM due to the different decomposition rates of SOM as a result of variety in its nutrient quality. These spatial predictions enhance the understanding of soil properties’ distribution in Germany.

Long-term warming in a temperate forest accelerates soil organic matter decomposition despite increased plant-derived inputs

Climate change may alter soil microbial communities and soil organic matter (SOM) composition. Soil carbon (C) cycling takes place over multiple time scales; therefore, long-term studies are essential to better understand the factors influencing C storage and help predict responses to climate change. To investigate this further, soils that were heated by 5 °C above ambient soil temperatures for 18 years were collected from the Barre Woods Soil Warming Study at the Harvard Forest Long-term Ecological Research site. This site consists of large 30 × 30 m plots (control or heated) where entire root systems are exposed to sustained warming conditions. Measurements included soil C and nitrogen concentrations, microbial biomass, and SOM chemistry using gas chromatography–mass spectrometry and solid-state 13C nuclear magnetic resonance spectroscopy. These complementary techniques provide a holistic overview of all SOM components and a comprehensive understanding of SOM composition at the molecular-level. Our results showed that soil C concentrations were not significantly altered with warming; however, various molecular-level alterations to SOM chemistry were observed. We found evidence for both enhanced SOM decomposition and increased above-ground plant inputs with long-term warming. We also noted shifts in microbial community composition while microbial biomass remained largely unchanged. These findings suggest that prolonged warming induced increased availability of preferred substrates, leading to shifts in the microbial community and SOM biogeochemistry. The observed increase in gram-positive bacteria indicated changes in substrate availability as gram-positive bacteria are often associated with the decomposition of complex organic matter, while gram-negative bacteria preferentially break down simpler organic compounds altering SOM composition over time. Our results also highlight that additional plant inputs do not effectively offset chronic warming-induced SOM decomposition in temperate forests.

Improved Characterization of Soil Organic Matter by Integrating FT-ICR MS, Liquid Chromatography Tandem Mass Spectrometry, and Molecular Networking: A Case Study of Root Litter Decay under Drought Conditions.

Understanding of how soil organic matter (SOM) chemistry is altered in a changing climate has advanced considerably; however, most SOM components remain unidentified, impeding the ability to characterize a major fraction of organic matter and predict what types of molecules, and from which sources, will persist in soil. We present a novel approach to better characterize SOM extracts by integrating information from three types of analyses, and we deploy this method to characterize decaying root-detritus soil microcosms subjected to either drought or normal conditions. To observe broad differences in composition, we employed direct infusion Fourier-transform ion cyclotron resonance mass spectrometry (DI-FT-ICR MS). We complemented this with liquid chromatography tandem mass spectrometry (LC-MS/MS) to identify components by library matching. Since libraries contain only a small fraction of SOM components, we also used fragment spectral cosine similarity scores to relate unknowns and library matches through molecular networks. This integrated approach allowed us to corroborate DI-FT-ICR MS molecular formulas using library matches, which included fungal metabolites and related polyphenolic compounds. We also inferred structures of unknowns from molecular networks and improved LC-MS/MS annotation rates from ∼5 to 35% by considering DI-FT-ICR MS molecular formula assignments. Under drought conditions, we found greater relative amounts of lignin-like vs condensed aromatic polyphenol formulas and lower average nominal oxidation state of carbon, suggesting reduced decomposition of SOM and/or microbes under stress. Our integrated approach provides a framework for enhanced annotation of SOM components that is more comprehensive than performing individual data analyses in parallel.

Changes in the Composition of Soil Organic Matter after the Transformation of Natural Beech Stands into Spruce Monoculture

The composition of soil organic matter is considered to have a key influence on C sequestration and global climate change and can be associated with changes in vegetation cover in the terrestrial ecosystem. Our study aimed to evaluate the soil chemical structures and various organic components from available or reactive to more stable forms in forest soils affected by acidification and after conversion from fairly close to natural beech (Fagus sylvatica) stands to a spruce (Picea abies) monoculture. Our results revealed that the beech stands had higher contents of dissolved organic carbon and low molecular mass organic acid compared to the spruce stands. The aliphatic CH groups within the soluble alkaline-extractable organic substance (AEOS) gradually disappeared with deeper soil horizons under both forest species, while the presence of aliphatic CH groups in the low-solubility AEOS was more pronounced in the A horizon under spruce and relatively increased with depth under beech stands. The carboxylic groups were more prevalent in deeper soil horizons, while polysaccharide chains and nitrogen functional groups decreased with depth under both forest stands but were more prevalent under beech than under spruce stands. These findings suggest that the stability of organic matter through the forest soil profiles increased due to the transformation of various organic compounds from litter to more stable organic matter with higher amounts of lignin components to greater amounts of carboxylic groups and aromatic groups in deeper soil horizons. Furthermore, a higher number of mobile components of soil organic matter and carboxylic acids, together with lower pH and cation exchange capacity under spruce, resulted in the leaching of nutrients, releasing risk elements into the soil solution and accelerating the podzolization process.

Soil organic matter components and sesquioxides integrally regulate aggregate stability and size distribution under erosion and deposition conditions in southern China

Water erosion considerably affects the stability and particle size distribution of soil aggregates, but the underlying mechanisms of water erosion remain unclear. To this end, we selected four landscape positions (top-, up-, mid-, and toe-slope) with distinct erosion and deposition characteristics on a typical eroded slope in southern China to conduct experiments- aiming to investigate the main drivers of soil aggregate stability during erosion and deposition processes. Soil samples were collected from 12 sites, and 4 size classes (>2, 2–0.25, 0.25–0.053, and <0.053 mm) of soil aggregates were obtained using the wet sieving method. The composition and stability of the soil aggregates, as well as the contents of organic (organic matter components) and inorganic (iron-aluminum oxides) cementing materials of different particle sizes, were determined. The results indicated that erosion significantly reduced the aggregate stability and the >0.25 mm water-stable aggregate content (WR0.25) (P < 0.05). The mean weight diameter (MWD) and geometric mean diameter (GMD) values of the soil aggregates at the eroding site decreased, and the fractal dimension (FD) increased. Furthermore, erosion markedly reduced the humic acid (HA) and fulvic acid (FA) contents in the bulk soils and soil aggregates, while the HA content showed no obvious difference between the eroding and depositional sites. In addition to the presence of complexed iron/alumina oxides (Fep/Alp), erosion markedly reduced the contents of amorphous (Feo/Alo) and free-form (Fed/Ald) iron/alumina oxides in the bulk soils and size fractions. Moreover, Fed/Ald, Fep and Feo/Alo were present in the microaggregates, while Alp was found in the macroaggregates. Additionally, boosted regression tree (BRT) analysis indicated that FA (36.70 %), Feo (19.00 %), and Ald (12.71 %) were the crucial predictors of soil aggregate stability. These findings further confirm that the organic and inorganic cementing materials in red soils collectively contribute to aggregate stabilization under the impact of erosion. This study facilitates a deeper understanding of the mechanisms governing soil aggregate stability in eroded landscapes, and provides a theoretical basis for biogeochemical cycling processes.

Impact of future scenarios of climate change on lignin dynamics in soil: A case study in a Mediterranean savannah

Lignin is an abundant and recalcitrant biopolymer of major relevance as soil organic matter (SOM) component playing a significant role in its stabilization. In this work, a factorial field experiment was established, where three climatic treatments (W, warming; D, drought; W + D, warming + drought), mimicking future climate change scenarios were installed over five years in a Mediterranean savannah “dehesa”, accounting for its landscape diversity (under the tree canopy and in open grassland). A combination of analytical pyrolysis (Py-GC/MS) and the study of biogeochemical proxies based on lignin monomers is used for the direct detection of lignin-derived phenols and to infer possible shifts in lignin dynamics in soil. A total of 27 main lignin-derived methoxyphenols were identified, exhibiting different patterns and proportions, mainly driven by the effect of habitat, hence biomass inputs to SOM. An accelerated decomposition of lignin moieties –(exhibited by higher LG/LS and Al/K + Ac ratios)– is particularly exacerbated by the effect of all climatic treatments. There is also an overall effect on increasing lignin oxidation of side chain in syringyl units, especially under the tree canopy due to the alteration in biomass degradation and potential stimulation of enzyme activities. Conversely, in open grassland these effects are slower since the microbial community is expected to be already adapted to harsher conditions. Our findings suggests that climate change-related temperature and soil moisture deviations impact soil lignin decomposition in dehesas threatening this productive Mediterranean agroecosystem and affecting the mechanism of soil carbon storage.

Review on The Impacts of Biochar and Soil Organic Matter (SOM) Habitation toward the Soil Physico-Chemical Properties Conjugating with Maize (Zea mays) Growth Performance

This study studies the complex relationships between maize growth, soil organic matter, and soil physico-chemcial properties, with an emphasis on biochar. It examines how soil organic matter affects pH, bulk density, Cation Exchange Capacity (CEC), porosity, and nutrient levels. Biochar and soil organic matter increase soil pH by decomposing organic anions. With biochar, increasing soil organic matter concentration reduces bulk density, improving soil structure, porosity, and water retention. By increasing Cation Exchange Capacity (CEC), biochar and soil organic matter improve soil nutrient retention and delivery, which is essential for soil fertility. As a soil organic matter component, biochar provides macro and micronutrients, boosting soil production. The study also highlights the importance of soil porosity in plant growth, with sandy soils having high porosity and leaching susceptibility and soil organic matter. However, loam soils, made of sand, clay, and silt, have a balanced porosity and soil organic matter concentration that makes them ideal for agriculture. These data show how organic matter, and biochar, affect maize growth and soil physico-chemical properties. This finding has major implications for protecting the environment and sustainable agriculture.

Design and performance of micro-zone C diffusion device to explore the importance of distance for soil microorganisms to utilize available exogenous carbon source

Soil acts as both a major sink and source of carbon in terrestrial ecosystems. Soil microorganisms play an important role in carbon sequestration as well as carbon mobilization. Either substrate to microbe or microbe to substrate transport are important in barren soil environments. Available external carbon sources can be utilized before some soil organic matter components are activated. In this process, external carbon source availability markedly determines soil microorganism activity (e.g., the distance between the carbon source and soil microorganisms). Here, I investigated the role of space as a factor influencing carbon utilization. I designed a soil incubation device that both separated the carbon source from soil microbes and ensured free carbon movement. Dextran was applied to avoid mass flow and maintain a balanced water potential. An isotope-labeling technique was used to quantitatively study carbon diffusion. The microcosm experiment verified that the carbon source was gradually utilized by the soil microorganisms according to the distance gradient. Soil microorganisms close to the carbon source initially used glucose, whereas more remote microbes waited for glucose to be transported. The microbial biomass carbon (MBC) content was much higher at smaller (0–0.5 cm) distances than they did at larger (0.5–1 or 1–2 cm) ones, which indicated that the higher concentration of available carbon source in the space closer to the glucose was conducive to the rapid acquisition and assimilation of microorganisms. The findings of this study establish a methodology and identify potential applications for further analysis of the spatial effects of carbon source availability on soil microbial activity.

Constraints and Drivers of Dissolved Fluxes of Pyrogenic Carbon in Soil and Freshwater Systems: A Global Review and Meta‐Analysis

AbstractPyrogenic carbon (PyC) is a significant component of the global soil carbon pool due to its longer environmental persistence than other soil organic matter components. Despite PyC's persistence in soil, recent work has indicated that it is susceptible to loss processes such as mineralization and leaching, with the significance and magnitude of these largely unknown at the hillslope and watershed scales. We present a review of the work concerning dissolved PyC transport in soil and freshwater. Our analysis found that the primary environmental controls on dissolved PyC (dPyC) transport are the formation conditions and quality of the PyC itself, with longer and higher temperature charring conditions leading to less transport of dPyC. While correlations between dPyC and dissolved organic carbon in rivers and other pools are frequently reported, the slope of these correlations was pool‐dependent (i.e., soil‐water, precipitation, lakes, streams, rivers), suggesting site‐specific environmental controls. However, the lack of consistency in analytical techniques and sample preparation remains a major challenge to quantifying environmental controls on dPyC fluxes. We propose that future research should focus on the following: (a) consistency in methodological approaches, (b) more quantitative measures of dPyC in pools and fluxes from soils to streams, (c) turnover times of dPyC in soils and aquatic systems, and (d) improved understanding of how mechanisms controlling the fate of dPyC in dynamic post‐fire landscapes interact. With more refined quantitative information about the controls on dPyC transport at the hillslope and landscape scale, we can increase the accuracy and utility of global carbon models.

Soil organic matter components and characteristics of forest soil in spruce and sycamore plantations in the temperate region

The stability of soil organic matter (SOM) that governs soil organic carbon (SOC) storage depends on its characteristics and components, but little is known about how tree species in forest ecosystems affect SOM components and characteristics. In this study, we used FTIR spectroscopy to investigate plantations of two ecologically and economically significant tree species—namely, spruce (Picea spp.) and sycamore (Acer pseudoplatanus)—in order to determine how the different litter inputs and root-microbe interactions of these two plantations affect the functional groups, components, and characteristics of their SOM. Soil samples were taken from the topsoil (0–10 cm) and subsoil (10–20 cm). In the 0–10 cm soil depth, the SOM's hydrophilic, hydrophobic, and aromatic components differ between the spruce and sycamore plantations. The hydrophobic components constitute the primary constituents of the SOM of the two forest plantations, in contrast to the expected predominance of the hydrophilic component of the SOM. Also, the high hydrophobicity (hydrophilic/hydrophobic) in the subsoil of the spruce plantations was attributed to a decrease in hydrophilic components and a subsequent increase in hydrophobic components of the SOM. The sycamore plantations exhibited a higher SOM aromaticity and a greater degree of decomposition than the spruce plantations. The aforementioned distinctions emphasise the contrasting mechanisms involved in transforming and turnover of the two-tree species' soil organic matter (SOM).

The Use of Spectroscopic Methods to Study Organic Matter in Virgin and Arable Soils: A Scoping Review

The use of modern spectroscopic methods of analysis, which provide extensive information on the chemical nature of substances, significantly expands our understanding of the molecular composition and properties of soil organic matter (SOM) and its transformation and stabilization processes in various ecosystems and geochemical conditions. The aim of this review is to identify and analyze studies related to the application of nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopy techniques to study the molecular composition and transformation of organic matter in virgin and arable soils. This article is mainly based on three research questions: (1) Which NMR spectroscopy techniques are used to study SOM, and what are their disadvantages and advantages? (2) How is the NMR spectroscopy technique used to study the molecular structure of different pools of SOM? (3) How is ESR spectroscopy used in SOM chemistry, and what are its advantages and limitations? Relevant studies published between 1996 and 2024 were searched in four databases: eLIBRARY, MDPI, ScienceDirect and Springer. We excluded non-English-language articles, review articles, non-peer-reviewed articles and other non-article publications, as well as publications that were not available according to the search protocols. Exclusion criteria for articles were studies that used NMR and EPR techniques to study non-SOM and where these techniques were not the primary methods. Our scoping review found that both solid-state and solution-state NMR spectroscopy are commonly used to study the structure of soil organic matter (SOM). Solution-phase NMR is particularly useful for studying soluble SOM components of a low molecular weight, whereas solid-phase NMR offers advantages such as higher 13C atom concentration for stronger signals and faster analysis time. However, solution-phase NMR has limitations including sample insolubility, potential signal aggregation and reduced sensitivity and resolution. Solid-state NMR is better at detecting non-protonated carbon atoms and identifying heterogeneous regions within structures. EPR spectroscopy, on the other hand, offers significant advantages in experimental biochemistry due to its high sensitivity and ability to provide detailed information about substances containing free radicals (FRs), aiding in the assessment of their reactivity and transformations. Understanding the FR structure in biopolymers can help to study the formation and transformation of SOM. The integration of two- and three-dimensional NMR spectroscopy with other analytical methods, such as chromatography, mass spectrometry, etc., provides a more comprehensive approach to deciphering the complex composition of SOM than one-dimensional techniques alone.

Meta-analysis of plant restoration impacts on soil microbial community structure in mining areas

Mining causes severe damage to soil ecosystems. Vegetation restoration in abandoned mine areas is an inevitable requirement for sustainable development. Soil microbes, as the most active component of soil organic matter, play a crucial role in the transformation of carbon, nitrogen, phosphorus, and other elements. They are often used as indicators to assess the extent of vegetation restoration in ecologically fragile areas. However, the impacts of vegetation restoration on soil microbial community structure in mining areas at the global scale remains largely unknown. Based on 310 paired observations from 44 papers, we employed the meta-analysis approach to examine the influence of vegetation restoration on soil microbial abundance and biomass in mining area. The results indicated that vegetation restoration significantly promotes soil microbial biomass in mining areas. In comparison to bare soil, vegetation restoration leads to a significant 95.1% increase in soil microbial biomass carbon and a 87.8% increase in soil microbial biomass nitrogen. The abundance of soil bacteria, fungi, and actinomycetes are significantly increased by 1005.4%, 472.4%, and 177.7%, respectively. Among various vegetation restoration types, the exclusive plan-ting of trees exhibits the most pronounced promotion effect on soil microbial biomass and population, which results in a significant increase of 540.3% in soil fungi and 104.5% in actinomycetes, along with a respective enhancement of 110.3% and 106.4% in microbial biomass carbon and nitrogen. Model selection results revealed that soil satura-ted water content and vegetation restoration history contribute most significantly to the abundance of soil bacteria and fungi. Soil available nitrogen has the most significant impact on the abundance of actinomycetes and microbial biomass carbon, while soil available phosphorus emerges as a crucial factor affecting microbial biomass nitrogen. This research could contribute to understanding the relationship between vegetation restoration and the structure of soil microbial communities in mining areas, and providing scientific support for determining appropriate vegetation restoration types in mining areas.

Addition of Biochar and Fertiliser Drives Changes in Soil Organic Matter and Humic Substance Content in Haplic Luvisol

Humic substances (HSs) constitute a primary component of soil organic matter (SOM) and play a crucial role in soil formation and fertility. However, comprehensive information regarding quantitative and qualitative changes in HS following biochar’s application to soil still needs to be improved. This study reports on the impact of biochar application at rates of 0, 10, and 20 t ha⁻1 (B0, B10, B20), both with and without nitrogen fertilisation at varying levels (N0, N1, N2), on SOM and HS contents throughout the cropping seasons between 2014 and 2019. The findings reveal changes in SOM and HS contents due to biochar addition and fertilisation. Notably, the most substantial increase in soil organic carbon content was observed in the B20N1 and B10N1 treatments, in stark contrast with the reference B0N0 treatment. A decrease in humification of SOM was noted across all treatments involving biochar, whether alone or combined with different N fertilisation levels. An interesting positive change in HS contents was observed in B10N2, where an increase in humic acids and a decrease in fulvic acids enhanced HS stability and improved HS quality. These findings shed light on the intricate dynamics of SOM and HSs in response to biochar application and nitrogen fertilisation over multiple vegetation seasons of crops on loamy Haplic Luvisols in Central Europe.

Variations in the quantity and chemical composition of soil dissolved organic matter along a chronosequence of wolfberry plantations in an arid area of Northwest China

AbstractBackgroundDissolved organic matter (DOM) is the most active component of soil organic matter (SOM), playing a major role in regulating soil fertility and carbon cycling. However, the effects of different wolfberry (Lycium barbarum L.) planting ages on the chemical diversity of DOM and its interaction with soil physicochemical properties have not been comprehensively studied. In this context, we collected soil samples (0–10 cm) from wolfberry orchards at different planting ages (1, 4, 6, 10, and 13 years) and from a corn field (0 years) in the arid region of Northwest Ningxia in China to assess the changes in soil DOM quantity and quality using ultraviolet–visible absorbance, fluorescence spectroscopy, and parallel factor analysis.ResultsWe found that the ages of the wolfberry plantation changed the contents of soil nutrients and SOM. In addition, significantly higher DOM concentrations were observed at wolfberry planting ages of 10 and 13 years than those in the control group (0 years) by 176.6 and 190.2%, respectively. The specific ultraviolet absorbance at 254 nm (SUVA254) and 254 nm to 365 nm ultraviolet absorbance ratio (E2/E3) values were decreased and increased, respectively, after wolfberry planting, indicating low aromatic and molecular weight compounds of soil DOM. The biogenic index (BIX) and fluorescence index (FI) of soil DOM ranged from 0.6 to 0.7 and 1.42 to 1.93, respectively, suggesting a combination of allochthonous and autochthonous sources. The short- and long-term wolfberry cultivations of 1 and 4 years decreased and increased the humification degrees of soil DOM, respectively. The contribution rate of the protein-like (C1) fluorescence intensity decreased, while that of the fulvic acid-like component (C3) increased with increasing wolfberry planting age, suggesting a change in the structure of soil DOM from protein-like to fulvic acids. In this study, total nitrogen (TN) and exchangeable Ca2+were the main factors affecting the quantity and quality of soil DOM in the wolfberry orchards with different planting ages.ConclusionsThis study demonstrated that long-term wolfberry plantation enhances the accumulation of soil DOM and more complex compounds, thereby promoting soil organic carbon sequestration under different planting ages and land-use types in terrestrial ecosystems.Graphical Abstract

Humic and Fulvic Acids Promote Growth and Flowering in Petunias at Low and Optimal Fertility

Humic substances are components of soil organic matter that influence soil structure and fertility. Humic and fulvic acids can be extracted from soil and other organic sources, and are used as biostimulants to promote plant growth and increase nutrient availability and uptake. The goal of this study was to determine whether selected humic and fulvic acid–based commercial products would promote growth and flowering of petunia (Petunia ×hybrida) ‘Picobella Blue’ grown in soilless media with low or optimal fertilizer rates. Plants were grown in 11.4-cm pots filled with peat-based media [80:20 peat:perlite (v/v); pH 5.4]. Three biostimulant products were evaluated at different rates and application frequencies: Huma Pro, a liquid humic acid biostimulant; Fulvi Pro, a liquid fulvic acid biostimulant; and Micromate, a powder containing both humic and fulvic acids. In Expt. 1, Huma Pro and Fulvi Pro were drenched weekly onto the growing media at a rate of 5, 10, or 20 mL⋅L–1; Micromate was drenched weekly at a rate of 5, 10, 20, or 40 g⋅L–1. Plants were fertilized with either 50 mg⋅L–1 nitrogen (N) (low fertility) or 100 mg⋅L–1 N (optimal fertility) from Jack’s Professional 20N–1.3P–15.7K Petunia FeED each irrigation. Control plants received fertilizer but no biostimulant treatments. In Expt. 2, biostimulant treatments were drenched once at transplant, biweekly, or weekly at a rate of 1.25, 2.5, 5, or 10 mL⋅L–1 for Huma Pro and Fulvi Pro; and at 5, 10, 20, or 40 g⋅L–1 for Micromate. All plants received constant liquid feed at the lower fertilizer rate of 50 mg⋅L–1 N. In Expt. 1, plants fertilized with 100 mg⋅L–1 N and treated with 20 g⋅L–1 Micromate had the best performance. The average shoot dry weight was 32% greater than that of the control plants. Micromate (20 g⋅L–1)-treated plants had an average of five more flowers per plant, and they flowered 4 days earlier than untreated control plants. In Expt. 2, plants treated with 40 g⋅L–1 of Micromate weekly had the greatest shoot dry weight compared with the other treatments. Weekly Micromate treatments (40 g⋅L–1) resulted in plants with an average of 13 more flowers per plant, which flowered 7 days earlier than control plants. Plants treated with Fulvi Pro and Huma Pro at 20 mL⋅L–1 had a significantly greater concentration of potassium in shoot tissue, whereas Micromate treatments at 20 and 40 g⋅L–1 resulted in a greater concentration of phosphorous in the shoots. The humic and fulvic acids in Micromate improved petunia crop quality by promoting vegetative growth, increasing flower numbers, and reducing the time to flower.

Functional organic matter components in mangrove soils revealed by density fractionation

ABSTRACT The mechanisms underlying stabilization of soil organic matter (SOM) in vegetated coastal ecosystems, including mangrove forests, are poorly understood, limiting our ability to predict the consequences of disturbances. Here, we introduce density fractionation to mangrove soils to identify the distribution and properties of the functional components of SOM regarding degradation state, stability, and origin, namely, the free low-density fraction (f-LF), mineral-associated LF (m-LF), and high-density fraction (HF). Three soil cores (1 m) were collected in a mangrove forest on Ishigaki Island, Japan, and cut into 10 cm intervals and analyzed. Although HF was the most abundant, the massive production of mangrove fine roots resulted in a high abundance of LFs throughout the cores, which markedly differed from terrestrial soils. Relative abundance of LFs together accounted for 38–66% of total soil C. The m-LF was as abundant as f-LF and 1.6 times higher in relative abundance than the global average of terrestrial soils. The C/N ratios and δ13C values clearly increased with depth in all fractions, which was attributed to the increased contribution from roots. We found a consistent pattern in Δ14C values of density fractions. HF was the oldest with Δ14C between −149‰ and −97‰ followed by m-LF (between −130‰ and −87‰) and then f-LF (between −89‰ and 78‰), suggesting that mineral association may be pivotal in long-term carbon storage in the mangrove mineral soil. Our analysis successfully identified meaningful functional components of mangrove SOM, yet several questions remained unanswered, including a large variability in Δ14C in different cores. Future studies would benefit from a coupled analysis of the quantity and quality of density fractions and geochemical factors in mangrove soils.