Humus substances in the swamp ecosystems of taiga zone of Western Siberia

Eutrophic peatlands with a predominantly humate type of humus is dominated according to content of hydrophobic humus substances accumulated in the solid phase of peat. Oligotrophic peatlands with fulvate type of humus are characterized by minimal storages. Mesotrophic peatlands occupy a transitional position, both in terms of storage and in terms of the humus type – humate-fulvate. Hydrophilic components of the water phase are characterized by fulvate humus, regardless of the type of peatland, but differ in the proportion of the contribution of humus substances in the amphiphilic system of swamp ecosystems. It is the highest in the thickness of the oligotrophic peatland almost 31%, slightly lower in the mesotrophic – 25% and much less in the eutrophic – 6%. Structural features of macromolecules of humic acids of swamp waters of various genesis are determined. The humic acids of mesotrophic waters are adjacent to the group of reduced compounds, they are more enriched with aromatic structures and carboxyl groups in relation to oligotrophic waters. The humic acids of oligotrophic waters belong to a group of oxygenated compounds, have low enrichment of nitrogen, contain more methoxyl carbon and carbohydrates (polysaccharides). These structural features are caused by geochemistry of waters feeding the peatlands and specific mechanisms of humic acids synthesis on the swamps of different genesis. The volume of dissolved organic carbon stock from wetland ecosystems through system of taiga rivers of left bank of Middle Ob is 805 kt per year.

Humus formation in soils of the Lena River Delta

The aim of the study. Nowadays close attention is paid to polar soils due to the expected landscape transformation rate under the predicted climate crisis. Intensive degradation of permafrost and the release of nutrients from their frozen state can lead to an increase in the emission of greenhouse gases into the atmosphere, as well as the loss of landscapes. The aim of the study was to investigate the peculiarities of organic residues formation and humification degree as well as humus structure and functioning in soil the Lena River Delta. Location and time of the study. The study was conducted on the Samoylov and Sardach Islands in the Lena River Delta (Yakutia, Russia). Field studies were performed during the summer of 2019. Objects and methodology. Soils of the Lena River Delta from the Samoylov Island (flooded area) and Sardakh (non-flooded zone), i.e. Subaquatic Fluvisol (Arenic) and Histic Cryosol (Siltic) were the objects of the study, respectively. To examine the features of humification chemical-analytical, sedimentation, micromorphological methods were used, as well as CP/MAS 13C-NMR spectroscopy. Main results. The data obtained indicate a high diversity of soils and soil formation conditions in the Lena River Delta. Under non-flooded conditions Histic Cryosol (Siltic) were formed in the flooded parts of the Samoylov Island, Subaquatic Fluvisol (Arenic) were formed. These soils play an important role in the global carbon cycle, accumulation, transformation and deposition of condensed high- and low molecular mass organic compounds in the composition of soils and permafrost. The main soil micromorphology features were identified. In the young landscapes the soil microstructure was represented by poorly sorted sand with a circular type of optical orientation of the soil plasma (which indicated the influence of the river), as well as vertically oriented micas (muscovite/biotite). Soils influenced by the floodplain process were characterized by the presence of coarse amorphous humus. Due to the long-term effect of the freezing/thawing processes on the permafrost-affected soils the biogenic aggregates were formed. In such organo-mineral microaggregates humus is fixed in the composition of mineral components consisting of particles of quartz, micas and Mn-Fe nodules and is in a stable state (physical stabilization of humus). To analyze the molecular composition the 13C NMR spectroscopy method was used. According to 13C NMR spectroscopy data, up to 37% of aromatic structural fragments accumulated in soils, which indicates the process of condensation of molecules in humic acids, thus showing a relatively high level of humus stabilization in the soils of the Lena River delta. From the data obtained, three main groups of chemical structural fragments that accumulate in the delta soils can be distinguished, such as C,H - alkyls ((CH2)n/CH/C and CH3), aromatic compounds (C–C/C–H, C–O) and the OCH group (OCH/OCq). In the studied humic preparations aliphatic structural fragments of HAs (63–64%) predominated, which indicated a deficiency of lignin and lignin-like compounds in the composition of humification precursors. The predominance of aliphatic structures is typical of humic substances formed under reduction conditions, including the aqueous humic substances, as well as in soils, the precursors of humification of which are typical tundra vegetation (mosses and lichens) with a predominance of carbohydrates (up to 80%). A significant amount of aromatic fragments accumulated in the delta in the alluvial soils of the first terrace of the river (flooded zone). This is apparently due to the formation of vascular plants in the flooded areas of the Lena River Delta. The chemical composition of vascular plants includes components such as tannins, flavonoids and lignin (arenas). Thus in the samples formed under vascular plants with a lignin content of about 30%, an increase in signals in the range of 110-160 ppm were observed. Aromatic and carboxyl fragments in the structure of HA were formed during the transformation of lignin, which leads to the resistance of HAs to biodegradation. Conclusion. Under the floodplain condition humus is represented by coarse amorphous forms, whereas without the influence of flooding humus is fixed in mineral microaggregates. Specific humic acids composition in the studied regions is determined by bioclimatic conditions, cryogenic processes and the composition of humification precursors. High abundance of aromatic structures in humus substances suggests relatively stable humus status (most likely due to the putative condensation of humic acids) in the Lena River Delta during the study period.

Molecular-mass distribution of humus acids of taiga soils

Purpose of the study: to reveal the influence of hydromorphism and agricultural use on the molecular-mass distribution (MMD) of humic (HAs) and fulvic acids (FAs) isolated from the soils of the European northeast of Russia. To assess the influence of the acidity of the medium on the MWD of FAs. Place and time of the event. The studies were carried out on the territory of the middle taiga (Maksimovsky station of the Institute of Biology of the Federal Research Center of the KSC UB RAS, located 8 km west of the city of Syktyvkar and the field of the Syktyvkar state farm, 5 km south-west of Syktyvkar, on the watershed of the Sysola and Vazhel-yu rivers) and northern taiga (3 km west of the Troitsko-Pechorsk station). The objects of the study were humic substances isolated from typical podzolic (Eutric Albic Retisol (Loamic)), gleypodzolic (Eutric Albic Stagnic Retisol (Loamic)), peaty-podzolic surface-gleyed (Eutric Albic Stagnic Histic) Retisol (Loamic Eutric Albic Retisol (Loamic)) soils. The soil sampling period is from 1 to 30 August 2014. Methodology. Quantitative analysis of the MMD of HA and FA preparations was performed using liquid size exclusion chromatography (gel chromatography) on Sephadex G-25 and G-100 gels with continuous automatic registration of the optical density of the eluate (λ = 280 nm) in a quartz flow cell, K 9 × 60 cm column (Pharmacia, Sweden). Distilled water, 0.05 M NaOH solution, and Tris-HCl buffer with pH = 8.2 were used as the eluent. Main results. Studies of the MMD of humic substances have been carried out. It was found that HAs contain three fractions with different molecular weights: ≥ 150 kDa, 73–80 kDa, and 13–23 kDa; FAs – two fractions: ≥ 5 kDa, 1–2 kDa. The low molecular weight of FAs, together with a large amount of oxygen-containing functional groups, contributes to their better solubility and migration ability in soils. The HAs of automorphic soils are characterized by a high content of low molecular weight fractions, and the proportion of the high molecular weight fraction in the HAs of the litter is 1.5–2.0 times higher than in the HAs of the podzolic horizon, which may be due to the migration of the low molecular weight fraction down the profile. The high proportion of the acidic low molecular weight fraction in the podzolic horizon promotes the decomposition of soil minerals and their leaching into the illuvial horizon. The influence of agricultural use of soils on the fractional composition of humic compounds is estimated. A sharp increase in the share of the high molecular weight fraction in the preparations of HAs of arable podzolic soil by 2–4 times compared with the HAs of virgin podzolic soils was noted, which is due to the cultivation of the arable horizon, the nature of the incoming plant residues and the increased microbiological activity of the developed soils. The effect of acidity of the medium on the character of chromatograms of FA preparations isolated from the main types of soils of the Komi Republic was studied. It has been shown that in the region of high pH values of the eluent 9–13, the absence of fractionation is associated with the association of FAs, a change in their conformation, and the effect of “over-exclusion”. Elution with distilled water (pH = 6.5) allows the separation of FAs into two fractions with molecular weights ≥ 5 kDa and 1–2 kDa.

Mineral-associated soil organic matter: characteristics and behavior under diagenesis

The main part of soil organic matter (OM) is mineral-associated: 88 ± 11% of С and even more – 93 ± 9% of N. The aims of the given study were: 1 – to demonstrate experimentally the adsorption selectivity of organic compounds towards minerals with different physico-chemical properties (palygorskite vs montmorillonite); 2 – to characterize mineral-associated OM of buried Late Holocene palaeosols and estimate its diagenetic transformations; 3 – to investigate the OM of humin from modern soils of different genesis and Pleistocene and Holocene palaeosols and estimate its diagenetic transformations. The basic soil properties were determined using standard methods. Clay fractions (<2 um) – natural organo-mineral complexes (OMC) were obtained by sedimentation, their mineralogy was studied by XRD. The elemental composition of OM was studied with CNS-analyzer. The structural characteristics of organic matter were determined with the solid-state 13C-NMR-spectroscopy and FTIR-spectroscopy, isotopic composition of C and N – by mass-spectrometry. The obtained results show that the characteristics of mineral-associated OM depends on the properties of mineral “filter” as well as the fate of OM under diagenesis: how long, in what quantity and quality it will persist. It was shown that palygorskite adsorbed predominantly O-alkyls, which are chemically strongly bound. As a result, the age of fulvic type humus in palygoskite palaeosols can reach 300 My. From other side humus of smectitic paleosols of the same age is present by deeply transformed aromatic structures (“coal”). Mineral-associated OM of buried under kurgans Holocene palaeosols contains more alkyls and carboxylic groups, is less aromatic in a comparison with OM of the respective soils. The specific feature of mineral-associated OM is its enrichment in N-compounds. The later are present by both vegetal and microbial compounds, and demonstrate the large affinity towards the mineral surfaces. The formation of chemical bounds between them provides the persistence of OM in OMC. E.g. H2O2 treatment results in preferential destruction of C-rich compounds and oxidized OM demonstrates larger C/N values. Mineral-associated OM of buried Holocene soils keeps the decreased values of C/N (7–14 vs 14–21 for OM of whole soils). Additionally they are characterized by heavier isotopic composition of δ15N in a comparison with the respective soils (5–11‰ vs 6–9‰). It could be explained either by the accumulation of microbial N, or increasing of the humification degree – the loss of aliphatic C and increasing of aromaticity. Humin is the considerable part of soil humus. Experimentally shown that OM of humins both of soils and OMC is enriched in O-alkyls and C of acetal groups. OM of humins are not homogeneous, and consists from at least two groups: mineral-associated OM and partly mineralized plant fragments. As a consequence, the content of humin in OMC is smaller in a comparison with respective soils. It is concluded that mineral-associated OM and humin as well as soil humus represent dynamic soil systems.

In memoriam of Denis Alexandrovich Gavrilov, a friend and a colleague

The article describes research and teaching activity of Denis Alexandrovich Gavrilov, Candidate of Biological Sciences, senior researcher with Soil Genesis Laboratory of the Institute of Soil Science and Agrochemistry of the Siberian Branch of the Russian Academy of Sciences, who died suddenly died young on August 26, 2021. He was also and enthusiastic and a hardworking publishing editor of the research journal Soils and Environment. The article briefly reviews of D.A. Gavrilov’s major publications presenting the results of his soil and combined soil and archeology studies, which he conducted both individually or in collaboration with other scientists from research and education institutions in Russia and Kazakhstan.

Using Decagon EC-5sensors for monitoring soil moisture

The aim of the study. To assess the possibilities of using the Decagon EC-5 sensor in research practice, especially under the conditions of its stationary installation; and to study with its help the dynamics of soil profile moistening and moisture migration under different weather conditions. Location and time of the study. The study was carried out on the territory of the Ust-Kamensky (forest-steppe) research station of the Institute of Soil Science and Agrochemistry of the Siberian Branch of the Russian Academy of Sciences (55.005507 N, 83.858635 E). The object of the study was the dark gray forest soil (Luvic Greyzemic Phaeozem). Five Decagon EC-5 sensors were installed at 9, 13, 18, 22 and 27cm depths in a small (30cm deep) soil pit and connected to the Em50 recorder. The necessary calibration was carried out beforehand. The sensors functioned from June 13 to July 7, 2017. Main results. The study showed that this device is suitable for a wide range of applications. According to the sensor readings, it was possible to trace the migration of moisture within the soil profile, as well as to differentiate it into gravitational and capillary water, as well as to establish the fact of precipitation with an accuracy of an hour and to calculate the precipitated amount. Statistical analysis of the obtained data showed low values of data variance and the coefficient of variation, which indicated high data homogeneity. The use of these sensors can improve the traditional flood method for determining the maximum soil water holding capacity. Moreover, detailed recording of soil moisture, provided by Decagon EC-5 sensors, in combination with Thermochron sensors for soil temperature recording, allows to study quantitative indicators of thermal gradient moisture flux at a new level. Conclusions. The study showed that Decagon EC-5 sensors comply with their technical specification and have good prospects for usage both in research and agricultural production. Provided its preliminary calibration and producing the calibration curves for the studied soils, the sensors allow quick and accurate measurement of the soil volumetric moisture content. The frequency and rate of sensor readings takes research on the dynamics and migration of moisture in soils to an entirely new level.

Soil biotest results using Azotobacter bacteria: interpretation problems and possible solutions

The aim of the study. The Azotobacter genus is a well-known bioassay for testing the soil environment quality. A large number of these bacteria is considered as evidence of the ecological well-being of a soil. However, a high number of these microorganisms was found in disturbed ecosystems, which means there is a problem of how to interpret the results of the biotest. Therefore the aim of the study was to clarify the causes of this problem and suggest a possible way to solve it. Location and objects of the study. The study was conducted in West Siberia (Russia) in the Priobskoe plateau (54°53'13.5"N, 82°59'36.7E"). Leached сhernozem with different content of organic matter (mortmass) was studied under the following treatments: 1) permanent fallow, 2) wheat cultivation, annual removal of straw from the field + summer fallow, 3) wheat + left straw + summer fallow, 4) wheat +left straw + green manure fallow, 5) grassland. The content of N-NO3, respectively, was equal to 50, 10, 15, 5, 0 mg/kg. Another object was a site at the mining and processing plant "Denisovsky" in South Yakutia (Russia) (56°46'20.23"N, 124°51'06.95"E). Abandoned for a long time (30 years) after coal mining spoils were studied in two variants: without plants and with well-developed vegetation cover. Total SOC content was 1.8 and 5.7%, N – 0.3 and 0.4 %, respectively. Methodology. The direct sowing of single soil aggregates onto the N-free medium containing glucose as C-source was used to cultivate Azotobacter. Glucose (10 mg/g soil) was added to the soil to activate Azotobacter growth. A live culture of bacteria was introduced into the soil at a dose of 1 ml/g to check the viability of Azotobacter in experimental soils. Main results. The status of the microbial community in situ was observed on microbial landscapes obtained by exposing slides in the undisturbed soil for 30 days. The overgrowth of soil lumps in the specified range of options was 0–80–40–0–0% and after glucose addition – 100–80–80–0%. The activation of Azotobacter growth after glucose addition was inversely proportional to the C: N ratio (between the mortmass and the mineral nitrogen). Live Azotobacter culture under grassland developed 2.5 times slower in comparison with the fallow. Similar patterns were found in the study of the soils developed on the coal mining spoils. Activation of Azotobacter growth by glucose (response to stress) was more pronounced in soils with apparently less favorable environment for bacteria. Conclusion. The reason behind misleading interpretation of Azotobacter biotest results was that the original purpose of the test was to assess fertility of arable soils. This role of the indicator bacterium was previously underestimated. It is known that the arable soil belongs to the category of disturbed ones, and the abundance of Azotobacter may indicate instability in the microbial community of the soil. To expand the capabilities of the biotest, the authors propose to supplement the test with a procedure for evaluating the Azotobacter growth response to experimental stress, e.g. C-substrate addition.

International conference «Soil as interlink for functioning of natural and anthropogenically transformed ecosystems» devoted to the 90th anniversary of the department of pedology and land resources estimation, Irkutsk State University and year of Baikal

From August 23 to August 29, 2021, Irkutsk hosted the Vth International Scientific and Practical Conference "Soil as interlink for functioning of natural and anthropogenically transformed ecosystems" (hereinafter – the conference) dedicated to the 90th anniversary of the Department of Soil Science and Land Resources Assessment of the Irkutsk State University (ISU) and the Year of Baikal. The total number of participants of the conference was 130 from 27 regions of Russia and 6 other countries (the Republic of Belarus, Bulgaria, Georgia, Moldova, Lebanon and Lithuania). The article presents a brief review of plenary and sectional reports on the following research topics: 1) theoretical soil science: genesis, evolution, classification problems; 2). multidisciplinary approaches of soil science related to the use of soil science methods in other research areas and scientific and industrial areas; 3) Soil resources and land assessment (fertility, degradation, land reclamation, qualitative and economic assessment, ecology and land protection). A total of 43 presentations were given at the conference: 8 plenary and 35 sectional. The interested reader will find a detailed description of the reports presented in this review, as well as other and other conference materials in the collection "Soil as interlink for functioning of natural and anthropogenically transformed ecosystems" (2021). A brief description of two excursions is given: (1) one excursion to the beautiful scenery at the shore of the Lake Baikal, held on August 23, 2021; (2) and another excursion at the Bratsk Reservoir on August 26-29, 2021. The purpose of the excursions wass to get acquainted with the nature and historical and cultural heritage of the Irkutsk region, Lake Baikal, as well as with soils, soil-forming rocks and natural features of the Southern Angara region. During the excursion tour, landscapes, rock outcrops and soil sections were presented: soils on a bumpy-depression relief; Paleolithic site of ancient man "Malta" with sections near the geoarchaeological objects "Malta-Bridge 3"; alluvial gray-humus soil in the floodplain of the Belaya River; exposure of Lower Cambrian rocks near the village Novomaltinsk; Cheremkhovsky coal mine; dispersed-carbonate gypseous chernozem near the Unga River; Novonukutsky gypsum mine; gray metamorphic soil and micellar-segregational chernozem on the bank of the Bratsk reservoir near the village Balagansk. At the end of the tour, the conference participants held a roundtable discussion about the problems of genesis and classification of the soils of the south of the Near-Angara region. The classification position of all the presented soils was justified within the framework of two classification systems: Classification of soils of Russia (2004) and Classification and diagnostics of soils of the USSR (1977). For scientific and informational support of the excursion, the guide "Southern Pre-Angara region: features of soil formation on rocks of different ages" (2021) was prepared and published. The conference aroused great interest among a wide range of specialists in the field of soil science, agrochemistry and ecology, land resource assessment, landscape studies, etc. The organization of such events promotes exchange of experience and strengthens the cooperation between researchers from leading universities and research centers, advancing the effective development of soil science, research methodology and practice, generalizing the information about soil as a link between the functioning of natural and anthropogenically transformed ecosystems.