Transformation Of Humic Substances Research Articles

Halophyte Elymus dahuricus colonization regulates microbial community succession by mediating saline-alkaline and biogenic organic matter in bauxite residue

Alkalinity regulation and nutrient accumulation are critical factors in the construction of plant and microbial communities and soil formation in bauxite residue, and are extremely important for sustainable vegetation restoration in bauxite residue disposal areas. However, the establishment and succession of microbial communities driven by plant colonization-mediated improvements in the physicochemical properties of bauxite residues remain poorly understood. Thus, in this study, we determined the saline-alkali properties and dissolved organic matter (DOM) components under plant growth conditions and explored the microbial community diversity and structure using Illumina high-throughput sequencing. The planting of Elymus dahuricus (E. dahuricus) in the bauxite residue resulted in a significant decrease in total alkalinity (TA), exchangeable Na, and electrical conductivity (EC) as well as the release of more tryptophan-like protein compounds and low-molecular-weight humic substances associated with biological activities into the bauxite residue substrate. Taxonomical analysis revealed an initial-stage bacterial and fungal community dominated by alkaline-tolerant Actinobacteriota, Firmicutes, and Ascomycota, and an increase in the relative abundances of the phyla Bacteroidota, Cyanobacteria, Chloroflexi, and Gemmatimonadota. The biological activities of phylum Actinobacteriota, Bacteroidota, and Gemmatimonadota were significantly associated with protein-like and UVA-like humic substances. As eutrophic bacteria, Proteobacteria participate in the transformation of humic substances and can not only utilize small molecules of organic matter and convert them into humic substances but also promote the gradual conversion of humic acids into simple molecular compounds. Our results suggest that plant roots secrete organic matter and microbial metabolites as the main biogenic organic matter that participates in the establishment and succession of the microbial community in bauxite residues. Root length affects bacterial and fungal diversity by mediating the production of protein-like substances.

Transformation of humic substances and functional groups of soil organic carbon after wildfire

ABSTRACT The composition of humic substances and structural diversity of soil organic carbon (SOC) can be affected by wildfire. In this study, soil samples were collected after 1 year of no fire, low intensity of fire (dead trees ≤ 30%), moderate intensity of fire (dead trees 30–70%) and high intensity of fire (dead trees ≥ 70%). The amounts of humic acid (HA), fulvic acid (FA) and humin (Hu) were investigated, and the characteristics of SOC were analyzed by 13C NMR spectroscopy too. The results showed that Hu decreased much more than HA and FA after fires, but it still contained more C than HA and FA. There was a positive correlation between the contents of SOC and Hu (R 2 = 0.96, p = 0.02). Aryl C of SOC decreased with the heavy intensity of fire, while alkyl C increased in converse. These results indicate that Hu loses more C than HA and FA with fires, while it is still the main component of SOC. The Alkyl C is more stable than aryl C in fires.

The effect of thinning on humus conditions in spruce and beech stands in the Highlands area of the Czech Republic

The study evaluates the effect of the type of thinning (above thinning vs. below thinning) on the humus conditions (i.e. forest floor stock, the content and stock of carbon and nitrogen, C/N ratio, and the proportion of carbon in humic substances) in spruce stands found on acid granodiorite (acid site) in forest vegetation zone (FVZ) 4 to 5 (Field research station Rájec-Němčice /FRS/, Department of Forest Ecology /DFE/ Mendel University in Brno) and in beech stands found on a solidified limestone sediment (nutrient rich site) in FVZ 3 to 4 (Training Forest Enterprise Masaryk Forest Křtiny /TFE Křtiny/); the sites indicated above are part of the upland of Drahanská vrchovina Upland (Czech Republic). Thinning was conducted in spruce stand in 2005, 2010; in beech stand in 2011. The stock of forest floor was determined to be 17–18 t.ha-1 under the beech stands and 51–54 t.ha-1 in the stands of spruce. The C/N ratio in the layers of forest floor and soil horizons at each site is similar and is not statistically significantly different. In spruce and beech stands in layers F and H fulvic acids prevail – a lower HA to FA ratio, the transformation of humic substances is more complete in layer H under spruce stands compared with beech. In the Ah horizon, the situation is reversed, with the transformation of humic substances being more complete under beech stands. The results incorporated using multivariate statistical methods (PCA) confirmed that thinning has no statistically significant effect on humus conditions in young spruce and beech stands in different types of habitats.

Transformation of humic substances of highly oxidized brown coal by basidiomycetes Trametes hirsuta and Trametes maxima

Transformation of humic substances of highly oxidized brown coal by basidiomycetes Trametes hirsuta and Trametes maxima

Problems of the control of volatile halogenated hydrocarbons in tap and waste waters

The concentration of volatile halogenated hydrocarbons in chlorinated tap water does not stay constant but increases during its passage through water supply systems, which indicates a certain incompleteness and the continuation of the transformation of humic substances upon the chlorination of water. The known official (certified) procedures, including the State Standard ones, seven in number, which are based on headspace gas chromatography, do not take into account such a peculiarity of tap water and deal with the quantification of free halogenated derivatives of hydrocarbons only. The comparative evaluation of official procedures is performed, and the sources of errors exceeding the acceptable level are inventoried; methods of optimization of all analytical steps are proposed to elaborate procedures ensuring the minimal error and reliable information on the concentration of volatile halogenated hydrocarbons in tap and waste waters.

Transformation of humic substances in soddy-podzolic soils under agrogenic impacts

The transformation of humic substances in soddy-podzolic soils under agrogenic impacts of different intensities and durations was studied. Indices of the initial stages of degradation and regradation of soil humus were revealed, and the humus status of soils under different fertilizing conditions was estimated.

Study of humic substance transformation in phosphatic soil in terms of nucleophilicity and electrophilicity

The applicability of the nucleophilicity/electrophilicity concept to the explanation of mechanisms of formation and transformation of humic substances was considered. Sequential time changes in the structure and properties of humic substances in phosphatic soil have been revealed. Different elemental composition of humic and fulvic acids at different stages of humus transformation was due to different patterns of electron density distribution in phosphorus-modified fragments of humic molecules. The important role of metals and phosphorus in realization of different pathways of humic substance transformation was demonstrated.

THE CHANGES WITH DEPTH OF HUMIC AND FULVIC ACIDS EXTRACTED FROM THE FINE EARTH AND ROCK FRAGMENTS OF A FOREST SOIL

Although much is known about the transformation of humic substances in the fine earth fraction of surface horizons, little is known about these processes in the coarse fragments (>2 mm) or about the changes with depth of humic and fulvic acids extracted from an entire soil profile. For each horizon of a forest soil developed on sandstone, the humic acids (HAs) and fulvic acids (FAs) were extracted from four fractions: fine earth, washing (i.e. fine material adhering to the clasts) and highly altered and slightly altered rock fragments. The HAs and FAs were also extracted from samples of the parent rock. The humic substances were then analyzed for their elemental composition and chemical structure by FT-IR and 13 C NMR spectroscopy. In the A horizons (upper 20 cm of the profile), the HAs from all the fractions appeared highly aromatic, with a high degree of C substitution and an abundance of carboxyl groups; however, the HAs of the rock fragments were more aromatic and richer in carbohydrate and proteinaceous residues than those of the fine earth. The HAs showed a more condensed and unsubstituted aromatic pattern at depth than in surface horizons. In the Bw and BCb horizons the contribution of biological residues to the humic substances seems to be progressively replaced by the contribution of organic materials derived from the sedimentary parent rock. The presence of features ascribable to the HAs and FAs of the parent rock decreased following the order: slightly altered clasts > highly altered clasts > washing > fine earth. Conversely, FAs showed a high homogeneity throughout the profile and are considered mostly of pedogenic origin. The chemical characteristics of both HAs and FAs showed a break in the trend with depth between Bw and BCb horizons, confirming the presence of a pedogenic discontinuity between the upper modern soil (A-Bw2 horizons) and the buried paleosol (BCb horizons).

Subaqueous Soils Pedogenesis in a Submersed Environment

Proposals for the inclusion of permanently submersed materials in soil taxonomic systems have periodically been put forth since some time in the mid 1800s. The proposals were largely conceptual in nature, relying more on subjective reasoning rather than analytical and field data. Advances in computer and global positioning technology, and the continuing development of the discipline of pedology provided the opportunity to examine shallow water estuarine sediments within a pedological framework. Morphological and analytical data from 85 1.5‐ to 2.0‐m profiles from Sinepuxent Bay, Maryland, indicate that the four pedogenic processes of additions, losses, transformations, and transfers outlined in the generalized theory of soil genesis are active in a subaqueous environment. The evidence of pedogenic processes includes the addition of biogenic calcium carbonate (shells), organic fragments, and organic matter; the loss of organic matter and surficial material; the transfer of oxygen through diffusion and bioturbation processes; and the transformation of humic substances and sulfur (sulfidization). The change in the concept of estuarine substrates from sediment to soil has significant ramifications for pedologists, ecologists, estuarine researchers, and government agencies involved in soil resource inventory and estuarine restoration programs. Application of these concepts could help further our understanding of the relationships between subaqueous soil distribution and submersed aquatic vegetation (SAV); clam, scallop, and oyster habitat; and dredge sites with potential acid‐sulfate weathering. This work resulted in a change to the definition of soil in Soil Taxonomy to include subaqueous soils that are capable of or presently support rooted SAV.

Humic substances distribution and transformation in forest soils

The distribution and transformation of humic substances in forest soils is investigated by CPMAS 13C NMR spectroscopy and chemical analyses. Studies on bulk soil samples and humic acid fractions indicate that different forest humus types result from different rates but similar pathways of litter decomposition. The main features of humification in the investigated forest humus profiles are preferential mineralization of carbohydrates, strong alteration of lignin leading to increasing proportions of carbon-substituted aromatic rings and loss of phenolic groups, increase in carboxyl group contents and accumulation of refractory alkyl components. The action of earthworms promotes transformation of plant residues to humic substances and incorporation of organic matter into stable organo-mineral complexes.