The biomass of fungal mycelium in buried paleosols and surface soils of the steppe zone

The contents of fungal mycelium have been studied in paleosols of ancient archeological monuments and in surface soils within the steppe, dry steppe, and desert zones of European Russia, on the Stavropol, Privolzhskaya, and Ergeni uplands. The buried paleosols date back to the Bronze Age (4600–4500 and 4000–3900 BP), the Early Iron Age (1900–1800 BP), and the early 18th century (1719–1721). The fungal mycelium has been found in all these paleosols. The biomass of fungal mycelium varies from 2 to 124 μg/g of soil. The distribution patterns of fungal mycelium in the profiles of buried paleosols and surface soils have been identified. It is shown that the dark-colored mycelium is typical of the ancient paleosols. In some cases, the content of the dark-colored mycelium in them may reach 100% of the total mycelium biomass.     

Age and activation of microbial communities in soils under burial mounds and in recent surface soils of steppe zone

Chestnut paleosols buried under steppe kurgans about 4800, 4000, and 2000 years ago and their background analogues were studied in the dry steppe zone on the Volga-Don interfluve. Morphological, chemical, microbiological, biochemical, and radiocarbon studies were performed. Paleoclimatic conditions in the region were reconstructed on the basis of paleosol data. The ages of microbial fractions isolated from the buried and surface soils were determined using the method of ¹⁴C atomic mass-spectrometry. It reached 2100 years in the A1 horizon of the buried paleosol, which corresponded to the archaeological age of the kurgan (1st century AD). The ages of microbial biomass isolated from the B2 horizons of the buried paleosol and the background surface soil comprised 3680 ± 35 and 3300 ± 30 years, respectively. The obtained data confirmed our assumption about preservation of microorganisms of the past epochs in the paleosols buried under archaeological monuments. It is ensured by various mechanisms of adaptation of soil microbial communities to unfavorable environmental conditions (anabiosis, transformation of bacteria into nanoforms, etc.). The possibility to stimulate germination of the ancient dormant microbial pool isolated from the buried paleosols by 2–3 orders of magnitude with the use of β-indolyl-3-acetic acid as a signal substance was demonstrated.     

Paleosol studies of burial mounds in the Ilovlya River valley (the Privolzhskaya Upland)

Paleosols buried under kurgans of the Bronze (end of the fourth and the third millennia BC), Early Iron (1st–3rd centuries AD), and Medieval (13th century AD) epochs have been studied on the Ilovlya River (a tributary of the Don River) terrace. The evolution of chestnut soils in the south of the Privolzhskaya Upland during the last 5000 years has been traced. It is shown that the mean weighted contents and distribution of soluble salts, gypsum, and carbonates in the soil profiles have been subjected to cyclic changes. The total microbial biomass and its trophic structure in the A1, B1, and B2k horizons of paleosols of different ages have been determined. A comparative analysis of the morphological, chemical, and microbiological data on the paleosols of different ages has been used to reconstruct the climatic dynamics for the last 50 centuries. The aridity of the climate in the studied region increased at the end of the third-the beginning of the second millennia BC and in the second and third centuries AD. The humidization of the climate took place in the 1st and in the 12th–13th centuries AD.     

Microbiological investigations of paleosols of archeological monuments in the steppe zone

Microbiological studies of the paleosols of archeological monuments (burial mounds) of the Neolithic, Bronze, Early Iron, and Middle Ages (the fourth millennium BC to the fourteenth century AD) located in the dry and desert steppe of the Lower Volga River basin were conducted. The microbial communities that existed at the time of creating the burial mounds were shown to be preserved up to the present time. This fact was confirmed by the regularities of the distribution of the microorganisms in the “mound-buried soil” system and by the data on the determination of the age for the microbial fraction of the paleosols using the method of ¹⁴C atomic mass spectrometry. The total biomass of the microbial communities in the paleosols amounted to 20–40% of the microbial biomass in their background analogues. In all the paleosols, a special pool of viable microorganisms was present. In the microbial community of the paleosols, the biomass of the active microorganisms corresponded to 0.30–41.0% of the biomass in the present-day soil; the content of mycelium of microscopic fungi composed 43–50% of that in the recent soil. In the mycelium structure in the paleosols, the share of the dark-colored mycelium increased to 98–100%. The microbiological parameters that give a contrasting characterization of the state of the microbial communities in the soils during the arid and humid climatic periods were revealed. The changes of the arid and humid climatic epochs were reflected in the structure of the microbial communities in the paleosols at the ecological-trophic, metabolic, and genetic levels.     

Phosphatase activity in the surface and buried chestnut soils of the Volga-Don interfluve

The phosphatase activity (PA) was studied in the chestnut paleosols buried in 1718–1720 under the Anna Ivanovna rampart in the southern part of the Privolzhskaya Upland and in the middle of the third millennium BC under the burial mound of the Bronze Age on the Northern Yergeni Upland; the background analogues of these soils were also examined. The PA values in the fresh soil samples varied from 2.5 to 37 mg of P₂O₅/10 g of soil per h with maximums in the A1 horizon of the surface soils and in the B1 horizon of the paleosols. The PA values depended on the time of storage of the samples: with time, they increased by 2.6–2.9 times in the A1 horizon of the background surface soil and decreased by 20–60% in the other soil samples. The specific distribution patterns of the PA values in the soil profiles remained the same independently of the time of storage of the samples. Relatively small amounts of the soil samples were sufficient for the reliable determination of the PA: 1–2 g for the A1 horizon and 3–5 g for the B1 and B2 horizons. The time of incubation with the substrate had to be increased up to 4 h for the long-stored samples.     

Characterization of the microbial communities in the modern and buried under kurgans soils of solonetzic complexes in the dry steppes of the Lower Volga region

The microbial communities were studied in the modern and buried under kurgans (1st century AD) soils of solonetzic complexes on the dry steppes of the northern part of the Yergeni Upland. It was found that the changes in the numbers of microorganisms from different trophic groups and in the biomass of the fungal mycelium along the profiles of the modern and buried solonetzic chestnut soils and solonetzes do not differ significantly. The quantitative estimate of the impact of the solonetzic process on the spatial variability of the microbiological parameters of the soils was given on the basis of the ANOVA. As a rule, the values of the microbiological parameters in all the horizons of the modern and buried chestnut soils were 1.2–2.8 times higher than those in the modern and buried solonetzes. The influence of the degree of solonetzicity of the buried paleosols on the microbiological parameters manifested itself in the entire profile, though in each particular horizon it was only seen in the numbers of some particular trophic groups of microorganisms. The comparison between the mean weighted values of the microbiological parameters in the entire soil profiles (the A1 + B1 + B2 horizons) demonstrated an inverse relationship between the population density of the microorganisms utilizing easily available organic matter and the degree of solonetzicity of the buried paleosols. The maximum biomass of the fungal mycelium was found in the solonetzic chestnut paleosol; it exceeded the biomass of the fungal mycelium in the other paleosols (which did not differ significantly in that parameter from one another) by 1.5–1.6 times.     

Biological Activity of Brown Semidesert Soils of the Baer Knolls

Eurasian Soil Science - We have evaluated the biological activity of brown semidesert soils (Eutric Cambisols (Loamic, Protocalcic)) of the Baer Knolls (Astrakhan oblast) formed under different...     

Evolution of soils and dynamics of the climate of steppes in the southeast of the russian plain during the late eneolithic and bronze ages (fourth to second millennia BC)

On the basis of studies of subkurgan pedochronoseries, the main mechanisms of the development of soils of arid and desert steppes in drained landscapes of the southeastern Russian plain in the Late Eneolithic and Bronze ages (6000−3000 years ago) were established. During the fourth to third millennia BC, evolution of soils took place at the level of subtypes with a shift of boundaries of soil subzones toward the north. In each of the studied natural regions (Central Russian Upland, Volga Upland, Ergeni Hills, and Caspian Depression), an increase in the aridization of the climate in the second half of the third millennium BC can be distinctly traced, owing to which a convergence of the topsoil with the transformation of dark-chestnut, chestnut, and light-chestnut soils in chestnut-like semiarid soils, which dominated the region 4200–3900 years ago, occurred. In the first half of the second millennium BC, another change in the conditions of soil formation occurred that was caused by an increase in the degree of atmospheric humidity. It induced the divergence of the topsoil with a secondary formation of areas of zonal chestnut soils and solonetzes in place of chestnut-like soils by the middle of the second millennium BC. The obtained data gives reason to suggest that the age of modern chestnut solonetz complexes of the region does not exceed 3500 years.     

Microbial biomass in soils of Russia under long-term management practices

 Non-tilled and tilled plots on a spodosol (C_org 0.65–1.70%; pH 4.1–4.5) and a mollisol (C_org 3.02–3.13%, pH 4.9–5.3), located in the European region of Russia, were investigated to determine variances in soil microbial biomass and microbial community composition. Continuous, long-term management practices, including tillage and treatment with inorganic fertilizers or manure, were used on the spodosol (39 years) and mollisol (22 years). Total microbial biomass (C_mic), estimated by the substrate-induced respiration (SIR) method, and total fungal hyphae length (membrane filter technique) were determined seasonally over a 3-year period. Long-term soil management practices (primarily tillage and fertilizer application) led to decreases in total microbial biomass (80–85% lower in spodosol and 20–55% lower in mollisol), decreases in the contribution of C_mic to C_org (2.3- to 3.5-fold lower in spodosol and 1.2- to 2.3-fold lower in mollisol), and 50–87% decreases in total fungal hyphae length compared to non-tilled control plots. The contribution of fungi to total SIR in virgin mollisol and fallow spodosol plots was approximately 30%. However, the contribution of fungi to SIR was approximately two times greater in tilled spodosol plots compared to a fallow plot. In contrast, the contribution of fungi to SIR in tilled plots of mollisol was less (1.4–4.7 times) than for a virgin plot. In summary, long-term soil management practices such as tillage and treatment with organic or inorganic fertilizers are important determinants of soil microbial biomass and the contribution of fungi to total SIR. Received: 28 April 1998     

Production of CO<Subscript>2</Subscript> by Paleosol Samples Taken in the Steppe Zone under Kurgans Constructed in the Periods of Relative Aridization and Optimum of the Climate

The studies of recent soils and paleosols buried under kurgans created in the periods of long-term aridization (3000–2000 BC) and climatic optimum (13th–14th centuries AD) were performed in steppes of the southeastern part of the East European Plain (Privolzhskaya Upland and Caspian Lowland) in order to determine the rate of carbon dioxide production by the soil samples at the natural moisture and after moistening up to 60% of the total moisture capacity. The CO₂ emission from the samples of paleosols corresponding to the period of climatic aridization in the Lower Volga River at their natural moisture status was lower than that from the samples of background surface soils, whereas the CO₂ emission from the samples of paleosols buried under optimum climatic conditions was higher than that from the samples of background surface soils. After moistening of the samples, the increase in the CO₂ emission from the paleosol samples depended on the actual humidity of the climate in the corresponding period.