Active Humus Research Articles

Contrasting occurrence of arsenic concentrations in Quaternary aquifers inside and outside the oxbow lakes along the middle reaches of the Yangtze river

Geogenic arsenic (As) contaminated groundwater poses a threat to drinking water safety and ecological health. Dissolved organic matter (DOM) plays a crucial role in As mobilization in Quaternary groundwater systems. Significant spatial variations in As concentrations in groundwater inside and outside the oxbow lakes were observed, but the controlling mechanisms remains unknown. In this study, carbon stable isotopes and fluorescence excitation-emission matrices (EEMs) combined with parallel factor analysis (PARAFAC) were used to elucidate the influence of DOM on contrasting occurrence of As in both inside and outside groundwater of the oxbow lakes along the middle reaches of the Yangtze River. The results showed that groundwater As concentrations outside the oxbow lakes (0.37–485 μg/L) were significantly higher than those in the groundwater inside (0.75–204 μg/L). Stable carbon isotopes suggest that methanogenesis promotes the reductive dissolution of As-bearing Fe(III) oxides/hydroxides, which is the primary process responsible for As enrichment in groundwater outside of oxbow lakes. In contrast, microbial fermentation dominated As mobilization in the groundwater inside of the oxbow lakes. The DOM in the groundwater outside of the oxbow lakes is characterized by a more reductive, predominantly more highly humified and less biologically active humus, while DOM in the groundwater inside consists mainly of microbial humic-like components that is less humified but more biologically active. This study provides new insight to decipher the controlling mechanism of As mobilization in the alluvial-lacustrine aquifers around typical oxbow lakes and is applicable to similar geogenic As-affected floodplain aquifer systems.

Composition, distribution, and source of organic carbon in surface sediments of Erhai Lake, China

Lake sediment is an important organic carbon (OC) sink. Nevertheless, few studies have been conducted on sediment organic carbon (SOC) in lakes, and the effects of environmental variables on SOC pools remain poorly understood. We combined physicochemical and spectroscopic analyses to investigate the composition, distribution, and source of OC in surface sediments of Erhai Lake, southwest China, and explored the relationships between environmental variables and its SOC pool. The SOC pool consists of relatively high proportions of labile organic carbon fractions, mainly from algal production, which are rapidly decomposed and exhibit high turnover rates. The relative content of humus carbon ranges from 13.5 % to 20.5 %, with fulvic acid carbon predominating (average 52.95 %), indicating weak humification and a relatively active humus carbon pool. The dissolved organic matter in water column and sediments of Erhai Lake is largely influenced by endogenous production, with a great contribution from phytoplankton. Surface sediments contained more protein-like components than overlying waters (80.0 % vs. 63.0 %), attributed mainly to abundant algal deposition and intense bacterial metabolism. Among environmental variables, sediment chlorophyll a showed the strongest relationship with the SOC pool, and was associated with rapid decomposition and promotion of the humification process, which supported the conclusion that algae had an important influence on the SOC pool. The SOC pool in the southern region of the lake is mainly contributed by algae, other microorganisms, and sewage, exhibiting a greater potential to release organic matters into the water column. The center and northern SOC pools show relatively stable characteristics and stronger OC sink capacity, mainly because of the input of terrestrial refractory organic matters from runoff. Our data shed light on the OC storage mechanisms in the surface sediments of Erhai Lake and provide theoretical bases for enhancing the OC sink of sediments in the lake.

Lignin Metabolism by Selected Fungi and Microbial Consortia for Plant Stimulation: Implications for Biologically Active Humus Genesis.

Plant lignin is regarded as an important source for soil humic substances (HSs). Nonetheless, it remains unclear whether microbial metabolism on lignin is related to the genesis of unique HS biological activities (e.g., direct plant stimulation). Here, selected white-rot fungi (i.e., Ganoderma lucidum and Irpex lacteus) and plant litter- or mountain soil-derived microbial consortia were exploited to structurally modify lignin, followed by assessing the plant-stimulatory activity of the lignin-derived products. Parts solubilized by microbial metabolism on lignin were proven to exhibit organic moieties of phenol, carboxylic acid, and aliphatic groups and the enhancement of chromogenic features (i.e., absorbance at 450 nm), total phenolic contents, and radical-scavenging capacities with the cultivation times. In addition, high-resolution mass spectrometry revealed the shift of lignin-like molecules toward those showing either more molar oxygen-to-carbon or more hydrogen-to-carbon ratios. These results support the findings that the microbes involved, solubilize lignin by fragmentation, oxygenation, and/or benzene ring opening. This notion was also substantiated by the detection of related exoenzymes (i.e., peroxidases, copper radical oxidases, and hydrolases) in the selected fungal cultures, while the consortia treated with antibacterial agents showed that the fungal community is a sufficient condition to induce the lignin biotransformation. Major families of fungi (e.g., Nectriaceae, Hypocreaceae, and Saccharomycodaceae) and bacteria (e.g., Burkholderiaceae) were identified in the lignin-enriched cultures. All the microbially solubilized lignin products were likely to stimulate plant root elongation in the order selected white-rot fungi > microbial consortia > antibacterial agent-treated microbial consortia. Overall, this study supports the idea that microbial transformation of lignin can contribute to the formation of biologically active organic matter. IMPORTANCE Structurally stable humic substances (HSs) in soils are tightly associated with soil fertility, and it is thus important to understand how soil HSs are naturally formed. It is believed that microbial metabolism on plant matter contributes to natural humification, but detailed microbial species and their metabolisms inducing humic functionality (e.g., direct plant stimulation) need to be further investigated. Our findings clearly support that microbial metabolites of lignin could contribute to the formation of biologically active humus. This research direction appears to be meaningful not only for figuring out the natural processes, but also for confirming natural microbial resources useful for artificial humification that can be linked to the development of high-quality soil amendments.

Regulation of agrophysical indicators of degraded sod-podzolic soil fertility using a system of fertilizers and predecessors

Experimental data on the dynamics of the most important agrophysical indicators of soil fertility which were obtained against the background of various fertilizer systems and predecessors in the development of degraded reclaimed lands that were withdrawn from circulation are presented. It has been shown that the rate of formation of a macrostructure that is valuable in production (0.25-10 mm) strongly depends on the amount of organic matter entering the soil in the form of high doses of all types of organic fertilizers, green manure and crop-root residues, upon decomposition of which an active humus is formed, which, when interacting with calcium, impregnates and cements the soil lumps, transforming them into a water-insoluble form. The greatest positive influence on the structural coefficient is exerted by cultivation of barley according to the organic background with the introduction of manure (40 … 80 t / ha) or liquid runoff of livestock complexes (120 t / ha) in combination with sowing application 10 kg a.v. P2O5 and 30 kg a.m. nitrogen as a top dressing per 1 ha. It has been established that in order to improve agrophysical parameters when degraded lands are involved in agricultural production, along with the introduction of high doses of organic fertilizers, crops with a deeply penetrating, powerfully developed root system that can not only condense the arable and plow layers, reduce acidity should be sown soil, but also at the same time improve its structure.

Effects of Quercus rubra L. on soil properties and humus forms in 50-year-old and 80-year-old forest stands of Lombardy plain

Besides the well-known effects on the native plant community, red oak may also impact the soil; the effects of afforestation with red oak involve both organic layers and mineral soil, resulting in changes in organic carbon quantity and quality and in soil acidification. Many alien species have become widespread in Europe; among these, red oak is a common invader of temperate forests. The effects of substitution of natural mixed forest by red oak forest on humus forms and soil properties were investigated in two paired plots: a 50-year-old (Bosco Vacaressino) and 80-year-old (Bosco Ginestre) forest stand. Soil sampling was performed from 3 layers at 40 and 49 points in Bosco Vacaressino and Bosco Ginestre respectively to determine humus forms, soil pH, organic carbon stock, carbon-nitrogen ratio (C:N), available phosphorus, and texture. Red oak resulted in a shift from Mull to Moder humus forms; soil acidification, higher C:N ratio, and soil organic carbon stock were observed compared with mixed forests. The major changes were reflected in a change toward less active humus forms; the effects of vegetation conversions were also visible in mineral layers; many of the modifications were more evident with increasing stand age.

Transformation of land resources as a result of anthropogenic impact

The article examined temporary matrices of transformation of soil processes related to the activity of microorganisms and humus in comparison with maternal matrices depending on age characteristics of man. The resulting match in value and productivity, from one year to 15 years, from 15 years to 40 years, from 40 years to 65 years, led to the idea of comparing human growth with soil zonal; Weights with indicators of activity of microbiological soil processes; Intelligence with active humus; Age with dynamics of development of temporary matrices on humus and microbiological activity. The dynamics of transformation of organic substances of upper soil horizons under the influence of agricultural use according to the general humus, taking into account their genesis, covers the period from 15 to 46 years; And on microbiological processes from 3 to 66 years. The conclusion is that the identification of human development with the development of soil-formation processes depending on their genesis brings us closer to a true understanding of our appearance, as a species possessing the power that can change the surrounding world through the noosphere in accordance with certain standards of transmutation.

Probabilistic assessment of the role of the soil degradation main factors in Kuban rice fields

As a result of reclamation systems for rice cultivation construction, the conditions of genesis and landscapes soil formation were radically violated. This led to the leaching of active humus and calcium, colloidal particles, nutrients from arable layer to underlying horizons, as a result of which there is a tendency to secondary salinization and solonization of soils. The development of the eluvial glue process and physicochemical parameters change of soils causes a change in the morphological soil profile. Currently relevant are preventing land degradation problems, maintaining and restoring soil fertility. In the article, the authors propose to characterize the rice irrigation system functioning mode from probabilistic point of view. They offer to evaluate the consequences of anthropogenic load, considering operational activities by Poisson stream of a certain intensity. This approach allows to consider uncertainty in terms of probability distributions. The function, characterizing soil quality S(t) was introduced. The function S(t) assumed to be monotonously decreasing. The probability R(S) of achieving a certain soil quality was considered. In case of minimum amount of humus Sm the soil is degrading. In these assumptions the average value expression and probability density of particular soil condition onset duration was received.

Electrode Potential Dependency of Single-Cell Activity Identifies the Energetics of Slow Microbial Electron Uptake Process.

Electrochemical measurements have been widely applied to study microbial extracellular electron transport processes. However, because electrochemistry detects not only microbial electron transport but also other reactions, background signals comparable to or larger than microbial ones hamper the identification of microbial electrochemical properties. This problem is crucial especially for the detection of electron uptake processes by slow-growing microbes in low-energy subsurface sediments, as the environmental samples contain electrochemically active humus and mineral particles. In this study, we report a cell-specific stable isotope analysis to quantify the electrode potential dependency of anabolic activity in individual cells for identifying the electron uptake energetics of slow-growing bacteria. Followed by the incubation of Desulfovibrio ferrophilus IS5 cells with isotopic 15N-ammonium as the sole N source on electrodes poised at potentials of -0.2, -0.3, -0.4, and -0.5 V [vs. standard hydrogen electrode (SHE)], we conducted nanoscale secondary ion mass spectroscopy (NanoSIMS) to quantify 15N assimilation in more than 100 individual cells on the electrodes. We observed significant 15N assimilation at potentials of -0.4 and more 15N assimilation at -0.5 V, which is consistent with the onset potential for electron uptake via outer-membrane cytochromes (OMCs). The activation of cell energy metabolism was further examined by transcriptome analysis. Our results showed a novel methodology to study microbial electron uptake energetics. The results also serve as the first direct evidence that energy acquisition is coupled to the electron uptake process in sulfate-reducing bacteria that are ubiquitous in the subsurface environments, with implications on the electron-fueled subsurface biosphere hypothesis and other microbial processes, such as anaerobic iron corrosion and anaerobic methane oxidation.

Effect of site conditions and tree species composition on physico-chemical properties of soil environment in the Western Carpathians area

The objective of pedological research conducted in the Kněhyně–Čertův mlýn National Nature Reserve was to verify to what extent the properties of the soil environment are influenced by: a) chemistry of soil-forming substrate, b) site conditions, c) species composition of forest stand. The results of this study document that the soil taxonomic units in the area of interest are of podzol character and that the altitudinal soil zonality has not developed there. The total content of basic macrobioelements in soil-forming substrates is not in correlation with their accessible fraction in top genetic horizons of the profile depth. The results of this study also show that lead content reaches a significantly hazardous boundary level at sites of ridge stands in the exposure of northern quadrants. The soil environment under forest stands with prevailing Norway spruce (Picea abies/L./ Karst.) is enriched with C-compounds and active humus in the entire profile more than the soil under stand types with prevailing European beech (Fagus sylvatica). In top horizons of soil Norway spruce influences significantly negatively humus quality (C:N) and also the content of accessible potassium which decreases in humification horizons below the limit of 200 mg∙kg-1.

Biological mineralization of organic matter in the modern virgin and plowed chernozems, buried chernozems, and fossil chernozems

The phenomenon of mineralization (biological mineralization) of organic matter in chernozems has been studied. A decrease in the content of Corg with time can be considered an index of the organic matter mineralization. It is suggested that the humus horizons of modern chernozems contain the pools of organic matter of different ages: easily decomposable organic matter, labile biologically active humus, stable biologically active humus, and relatively inert humus. The composition and mean residence times of these pools and their contribution to the total organic matter content have been estimated. The particular types of the biological mineralization have been determined on the basis of the comparison between the velocities of mineralization (M) and humification (H) processes: total unidirectional mineralization (M ≫ H), equilibrium mineralization (M ∼ H), nonequilibrium mineralization (M> <H), and zero mineralization. The separation of subtypes is based on data on the relative rates (%) of the organic matter mineralization. On the basis of available experimental data on chernozems buried under kurgans and in loess sediments (with the age of up to 800 ka), the quantitative relationship of the humus content in the buried soils on their age has been found; it has an exponential shape. During the first 100 ka after the soil burial, the soil humus content gradually (with a slowing intensity) decreases from 100–75 to 6.5% of its content in the virgin chernozems. Then, 100–1000 ka after the soil burial, the soil humus content remains approximately constant (6.5% of the initial level, or 0.3% of the soil mass). The rates of mineralization have been estimated. It is shown that the elemental composition (C, H, N, O) of humic acids remains relatively stable for a long time due to the regeneration of the chemical structure of humus (matric restoration of humus). It is suggested that several different forms of humus related to pedogenesis should be distinguished in the biosphere. The renewable humus in the equilibrium state with the environment is typical of the open biospheric (soil) systems. The fossil humus, whose content decreases with time, and whose composition remains stable, is typical of the semiclosed and closed systems. With time, it transforms into residual humus, whose content and composition remain stable. The fossilized organic matter in the fossil soils and sediments of the past geological epochs (Mesozoic and Paleozoic) considerably differs from the renewable, fossil, and residual humus.

A model simulation analysis of soil nitrate concentrations—Does soil organic matter pool structure or catch crop growth parameters matter most?

Three different soil organic matter (SOM) submodels were tested within the framework of the soil–plant–atmosphere model Daisy. The three submodels were: the original Daisy SOM module (OLD) with relatively non-dynamic humus pools, a recalibrated Daisy SOM module (STD) with the same pool structure as the original, but with a more rapid turnover of the active humus pool, and a newly developed SOM model structure (CNSIM), with inclusion of a soil microbial residuals pool of relatively rapid turnover, and a relatively recalcitrant added organic matter pool, producing a larger and more sustained residual N mineralisation. Furthermore, two different parameterisations of the catch crop submodules, differing in grass growth and N assimilation dynamics, were tested and the relative influence of SOM module or catch crop growth module on the simulated variables assessed. The simulations were carried out with data from a field experiment with four mixed cropping systems and compared to measured results of crop production, N uptake and soil nitrate concentration. The cropping sequence was 3 years of grassland (cut or grazed) followed by 3 years of spring cereals with ryegrass as a catch crop and two levels of fertiliser application. Independently of the SOM module, plant production and nitrogen uptake for cereals were simulated well. The dynamics of the added organic matter (AOM) and SOM of the two Daisy submodules were nearly identical, whereas the CNSIM submodule built much more nitrogen into the AOM pools, especially during the pasture years. During the period with spring barley, the CNSIM module simulated similar amounts of AOM as the other modules. In general, the simulated nitrate concentrations at 100 cm depth were higher than the measured values, but the changed dynamics in the CNSIM simulations resulted in even higher overestimation of the nitrate concentration than the two other modules. The choice of catch crop submodule had a considerable effect on nitrate concentration and therefore the potential for nitrate leaching, possibly overshading more futile differences produced by the different SOM submodules. The simulations show the importance of applying appropriate intercrop submodels when the model is used for simulating rotations with intercropping of grass-clover or undersown catch crops.

Humus Index as an indicator of forest stand and soil properties

The Humus Index, based on the visual assessment of topsoil horizons and a classification of humus forms, is a numerical score which can be used as a correlate of stand and soil properties. In oak stands from the Montargis forest (Loiret, France) we observed a good linear relationship of the Humus Index with most parameters describing stand development (age, basal area (BA), height and diameter at breast height of dominants) and soil type (depth of clay horizon). The relationship with parameters describing nutrient availability (exchangeable bases, base saturation) was similarly good but nonlinear. In the studied forest the Humus Index was affected first by stand age and second by soil type. When corrected for age and soil type, data (96 pooled estimates) indicated a slight decrease in the Humus Index (shift towards more active humus forms) in stands converted from old coppices-with-standards when compared with even-aged high forest.

Polycyclic aromatic hydrocarbons (PAH) in different forest humus types

The behavior of 20 PAH in the organic layers of a L mull, an Of mull and a mor was assessed by a combined approach of a soil profile study, and the analysis of particle-size separates. Increasing PAH concentrations with depth in the mor profile (L, 866 μg kg(-3); Of, 2902 μg kg(-1); Oh, 10489 ug kg(-1)) were assigned to selective enrichment during organic matter decomposition. PAH were further highly enriched within the finer separates. For the L horizons, significant positive correlations were established between the enrichment of individual PAH (as observed from the decomposition gradient between the >2-mm fraction and the < 0.05-mm fraction), and the KOW for each compound. The slope of the regression line, m, described the degree of differentiation between low- and high-molecular PAH during litter decomposition. Since m was greatest in the most biologically active humus type (L mull, 0.33) and smallest in the most inactive (mor, 0.20), microbial breakdown was assumed as the dominating process for this differentiation. The results also indicated that decomposition processes had already taken place in the L horizons, leading to morphological and chemical changes of organic matter, and to an enrichment of high molecular PAH.

Characterization of cultivation effects on soil organic matter

AbstractHumus properties in various Ap horizons from field plots, that have been cultivated in long‐term experiments under different management conditions, were investigated by pyrolysis‐field ionization mass spectrometry (Py‐FIMS) and 13C‐NMR spectroscopy. The results of Py‐FIMS were evaluated by correlation and principal component analysis from reproducible data sets of bulk soil samples and extracted humic substances, and allowed a distinct discrimination on the basis of humus quality and composition. The chemical subunits suitable for discrimination are the major plant constituents carbohydrates, lignin, and proteinaceous materials as well as their humification products. The contribution of these compound classes to soil organic matter decreased with the intensity of management. CPMAS and solution 13C NMR spectra of soils and humic substances demonstrated that with more intense management, both the intensities of the phenolic region (140–160 ppm) and the aromatic region (110–140 ppm) decreased. The combination of both independent methods MS and NMR, together with microbiological and biochemical data, yields the general result that intensive soil management leads to a less active humus.