The microbial biomass in paleosols buried under kurgans and in recent soils in the steppe zone of the Lower Volga region

The total microbial biomass (TMB) was assessed in the chestnut and light chestnut soils and in the paleosols under burial mounds (steppe kurgans) in the Lower Volga region on the basis of data on the organic carbon content in the extracted microbial fraction supplemented with the data on the extraction completeness as a conversion coefficient. The completeness of the microbial fraction extraction was determined by direct counting of the microbial cells and colony-forming units (on plates with soil agar). The total microbial biomass varied from 400 to 6600 μg of C/soil. Its values in the buried soils were 3–5 times lower than those in the surface soils. The TMB distribution in the buried chestnut soil profile was close to that in its modern analogue (with the minimum in the B1 horizon). In the buried light chestnut paleosols, the TMB values usually increased down the profile; in the recent light chestnut soils, the maximum TMB values were found in the uppermost horizon.     

Comparative characterization of microbial communities in kurgans,paleosols buried under them,and background surface soils in the steppe zone of the Lower Volga region

A comparative analysis of the state of microbial communities in kurgans, paleosols buried under them, and background surface soils in the dry steppe zone of the Lower Volga region has been performed. It is shown that the population density of microorganisms of various trophic groups in the kurgans is an order of magnitude lower than that in the A1 horizon of the corresponding buried paleosols and background surface soils within the areas of chestnut, light chestnut, and solonetzic soils. The respiration activity of the microbial communities in the upper layer of the kurgans is comparable with that in the A1 horizons of the background surface soils; it decreases in the deeper layers of the kurgans. In the A1 horizon of the buried paleosols, the respiration activity is approximately the same as in the deep layers of the kurgans. In the buried paleosols, the spatial variability in the numbers of soil microorganisms is approximately the same or somewhat higher than that in the background surface soils. The spatial variability in the respiration activity of the buried paleosols is two to four times higher than that in the background surface soils.     

Assessment of the living and total biomass of microbial communities in the background chestnut soil and in the paleosols under burial mounds

The contents of phospholipids and carbon of the total microbial biomass were determined in the modern chestnut soil and in the paleosols buried under mounds of the Bronze and Early Iron Ages (5000–1800 years ago) in the dry steppe of the Lower Volga River basin. Judging from data on the ratio between the contents of phospholipids and organic carbon in the microbial cells, the carbon content of the living microbial biomass was calculated and compared with the total microbial biomass and total organic carbon in the studied soils. In the background chestnut soil, the content of phospholipids in the A1, B1, and B2 horizons amounted to 452, 205, and 189 nmol/g, respectively; in the paleosols, it was 28–130% of the present-day level. The maximum content was measured in the paleosols buried 5000 and 2000 years ago, in the periods with an increased humidity of the climate. In the background chestnut soil, the total microbial biomass was estimated at 5680 (the A1 horizon), 3380 (B1), and 4250 (B2) μg C/g; in the paleosols, it was by 2.5–7.0 times lower. In the upper horizons of the background soil, the portion of the living microbial biomass in the total biomass was much less than that in the paleosols under the burial mounds; it varied within 8.5–15.3% and 15–81%, respectively. The portion of living microbial biomass in the total organic carbon content of the background chestnut soil was about 4–8%. In the paleosols buried in the Early Iron Age (2000 and 1800 years ago), this value did not exceed 3–8%; in the paleosols of the Bronze Age (5000–4000 years ago), it reached 40% of the total organic carbon.     

Agrogenic transformation of soils in the dry steppe zone under the impact of antique and recent land management practices

Virgin, cultivated, and old-arable soils have been studied in the area of Olbia, one of the antique poleis in the northern part of the Black Sea region. It is shown that the soils cultivated during the antique time still preserve some features differing them from their virgin analogues. In the course of agrogenic evolution, progressive changes in the morphology of dry steppe soils are not accompanied by the improvement of soil aggregation at lower levels. Macromorphological indices attest to the enhanced development of humification processes and leaching of carbonates and soluble salts in the soils cultivated during the antique time. At the same time, a number of soil degradation processes are vividly manifested in the cultivated soils. It is suggested that this process can be referred to as the soil allopseudomorphosis.     

Functional diversity of microbial communities in saline soils of the semidesert zone

The health status of microbial communities in soils of the Sulak Lowland (Dagestan) was estimated on the basis of data on their functional diversity. The health status of the microbial communities decreased in the following soil sequence: typical meadow soil > meadow-chestnut soil > dark chestnut soil > saline soil (solonchak). The low concentration of soluble salts (<1 meq/100 g of soil) had a positive effect on the functioning of the microbial communities. The health status of the microbial communities also depended on the soil humus content and pH conditions.     

Microbial biomass in paleosols under burial mounds as related to changes in climatic conditions in the desert-steppe zone

The contents of carbon in the total microbial biomass (C-TMB) and in the microorganisms reactivated with glucose (C-RG) and the portion of glucose-reactivated microorganisms in the microbial community (C-RG/C-TMB) were determined in paleosols buried under desert-steppe kurgans (burial mounds) 5100–3960 years ago and in the background surface light chestnut soils. In the paleosols, the corresponding indices reached 986 μg/g (C-TMB), 14.6 μg/g (C-RG), and 1.5% (C-RG/C-TMB) and were considerably lower than those in the background surface soil. The lowest values were found for the paleosols buried 4260–3960 years ago, which confirms a conclusion about the paleoecological crisis during this time interval.     

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.     

二甲基二硫熏蒸对保护地连作土壤微生物群落的影响

随着保护地高附加值经济作物的连年栽培, 土传病害问题愈发突出, 熏蒸剂也因此得以更广泛的应用。但鉴于熏蒸剂的广谱性, 在杀死有害生物的同时, 不可避免地对非靶标生物产生一定的影响。为明确溴甲烷替代药剂二甲基二硫(dimethyl disulfide, 简称DMDS)熏蒸对土壤微生物群落的影响, 本研究在室内条件下采用BIOLOG 方法, 测定不同浓度DMDS 熏蒸对保护地连作土壤微生物群落的影响。研究结果表明: 不同浓度DMDS(170.00 mg·kg^-1、85.20 mg·kg^-1、42.50 mg·kg^-1、21.30 mg·kg^-1 和10.62 mg·kg^-1)熏蒸处理对镰孢菌属(Fusarium spp.)和疫霉菌属(Phytophthora spp.)的LC₅₀(抑制中浓度)分别为42.08 mg·kg^-1 和115.15 mg·kg^-1。DMDS 熏蒸后恢复培养0 d 取样, 温育120 h 时, 170.00 mg·kg^-1、42.50 mg·kg^-1 和10.62 mg·kg^-1 的DMDS 处理土壤的AWCD 值(平均每孔颜色变化率, average well-color development, AWCD)分别比空白对照升高8.46%、6.02%、19.31%, 表明DMDS 促进了土壤微生物的生长。恢复培养14 d 后, 各处理土壤微生物的AWCD 值恢复至对照水平。多样性指数分析显示, DMDS 熏蒸后恢复培养0 d 时, 土壤微生物群落的Shannon 指数、Simpson指数均高于空白对照, McIntosh 指数与对照无显著性差异; 恢复培养7 d 后, Shannon 指数与Simpson 指数恢复至对照水平。主成分分析结果显示, DMDS 熏蒸后恢复培养0 d 时, 各处理间微生物对碳源的利用方式差异显著, 恢复培养14 d 后, DMDS 对微生物碳源利用方式的影响逐渐减弱, 恢复至对照水平。结果表明, DMDS 熏蒸处理对土壤微生物的生长具有促进作用, 影响了微生物对碳源的利用方式, 但在恢复培养14 d 后, 被干扰的土壤微生物逐渐恢复至对照水平。DMDS 熏蒸处理在有效防控土传病原真菌的同时, 不会对土壤微生物群落产生明显的扰动影响, 对环境较安全。     

Establishment of a landfill impact zone on soils using structural and functional modifications of microbial communities

A number of structural and functional parameters of microbial communities have been applied for ecological monitoring of soils located in nearby landfills. The difference in sensitivities to pollution between different microbial indices was shown. A landfill impact zone in the direction of pollution migration was established using the total disturbance index of habitat microbial communities.     

Forms of heavy metal compounds in soils of the steppe zone

A parallel scheme of extractions was used for determining heavy metal compounds in uncontaminated and artificially contaminated soils of Rostov oblast. A method for calculating the contents of complex and specifically adsorbed metal compounds from the difference in their concentrations in different extracts was suggested. It was found that the portion of firmly fixed metal compounds decreases and the portion of potentially mobile (exchangeable, complex, and specifically adsorbed) metal compounds increases with an increase in the degree of contamination of chernozems and chestnut soils with lead, copper, and zinc over a one-to two-year-long observation period. This was due to the capacity of heavy metal ions to substitute for the exchangeable cations in the exchange complex of the studied soils, to form complexes with the soil organic matter, and to participate in the specific adsorption. Some differences in the behavior of different metals were found.     

Production of CO<Subscript>2</Subscript> by surface and buried soils of the steppe zone under native and moistened conditions

Modern light chestnut and chestnut soils and their analogues buried under steppe kurgans in the southeastern part of the Russian Plain were studied in order to determine the rates of the CO₂ production by these soils under the native (with the natural moisture content) and moistened (60% of the total water capacity) conditions. It was found that the rates of the CO₂ production by the soil samples in the native state are relatively close to one another and vary from 0.3 to 1.4 μg of C/100 g of soil/h. The rates of the CO₂ production in the moistened state increased by two orders of magnitude for the modern surface soils and by an order of magnitude for the buried soils.     

The structural state of buried and surface soils of solonetzic complexes in the dry steppe zone of the Lower Volga basin

The structural state of modern (surface) soils and the soils buried under Anna Ioannovna??s rampart (1718?C1720) was studied. These soils are the components of solonetzic soil complexes in the southern Privolzhskaya Upland. The dehumification and the high content of calcium in the exchange complex determine the state of the macrostructure of the chestnut soil buried about 300 years ago. The dehumification drastically lowers the water stability of the soil aggregates, and the predominance of calcium ions in the soil exchange complex prevents the destruction of the chestnut paleosol aggregates and preserves their aggregate state upon moistening. For the last 300 years, no significant changes in the macrostructure of the solonetzes have been observed.     

Paleosols of kurgans of the Early Iron Age in the Transural steppe zone

Paleosol studies of archaeological monuments of different ages have been conducted on the Transural Plateau. The morphological and physicochemical properties of paleosols under burial mounds (kurgans) of the Early Iron Age (the fifth and fourth centuries BC) were compared with the properties of background surface soils. A paleosol of the Savromat epoch (2500 BP) is characterized by high contents of gypsum and soluble salts. The presence of humus tongues in its profile attests to the aridity and continentality of the climatic conditions during that epoch. Paleosols buried under kurgans of the Late Sarmatian epoch and the Hun epoch (about 1600 BP) are characterized by a higher content of humus and greater depth of the carbonate horizon, which attests to the humidization of climatic conditions. The evolution of soils as related to climate dynamics in the first millennium BC and the first millennium AD is characterized.     

缙云山森林土壤微生物数量与群落特征

本文以重庆市缙云山国家森林保护区的毛竹林、 马尾松针叶林、 马尾松针阔混交林为供试对象,研究了不同森林群落的土壤微生物数量、 群落特征及其与土壤养分的关系。结果表明,毛竹林土壤中的细菌、 放线菌、 真菌数量最多,混交林次之,针叶林最少,高低之间分别相差 32.3倍（细菌）、 19.2倍（放线菌）和19.3倍（真菌）。说明森林植被群落的生产力越高,枯枝落叶量越大,土壤微生物数量越多。在毛竹林土壤中,微生物的多样性指数、 均匀度指数和优势度指数显著高于针叶林和混交林,说明毛竹土壤的生态环境相对稳定良好,微生物种群丰富,密度较大,种群优势突出。此外,土壤微生物存在明显的季节变化,夏季最高,冬季最低,与土壤有效氮、 磷的季节变化基本耦合。土壤微生物数量与土壤有机质和碱解氮呈显著正相关（r有机质=0.592**~0.741**,r碱解氮=0.490*~0.581**,n=24）; 在毛竹林和混交林土壤中,土壤微生物数量与有效磷呈显著正相关（r毛竹林=0.461*,r 混交林=0.450*,n=24）,说明微生物在土壤有机质转化和氮、 磷供应过程中起重要作用,与森林植被群落的生产力密切相关。     

Changes in tolerance of soil microbial communities in Zn and Cd contaminated soils

Trace metals are present in the soil matrix in different forms, and this obscures the relationship between the amounts of metals, their biological availability and effects. Chemical methods have been devised to directly measure the biological available pools of trace metals, but such methods need to be validated against measured exposure of organisms in the soil. We studied acquired Zn- and Cd tolerance of the soil microbial community as a reporter of its exposure, and compared it with chemical determination of Zn and Cd in 10 soils differing in pH, organic matter content, texture, vegetation-/cultivation history and metal contamination. The tolerance was measured as LC₅₀ (i.e. the metal concentration which inhibits 50% of the activity) in suspensions of extracted soil bacteria, by measuring the incorporation rate of [³H] thymidine at different metal concentrations. Chemical determination of Cd and Zn in soils included total concentrations by aqua regia extractions (AR), and total concentrations in extracted pore water (PW). In addition was the ‘effective concentration’ (C_E) determined using the Diffusion Gradients in Thins films method (DGT). The LC₅₀ values correlated better with PW (r²=0.90 for Cd and r²=0.97 for Zn) and C_E (0.90 for Cd and 0.98 for Zn) compared to the correlation with AR (0.72 for Cd and 0.82 for Zn). After excluding a single extremely contaminated soil from the analysis, the correlation of LC₅₀ with AR was much poorer (r²=0.03 (ns) for Cd and r²=0.48 for Zn), whereas correlations remained significant for both PW (0.90 for Cd and 0.87 for Zn) and C_E (0.54 for Cd and 0.84 for Zn). In conclusion, PW fraction of Cd and Zn appear to be the best predictor of trace metal exposure of the soil microorganisms.     

Use of RAPD markers for the study of microbial community similarity from termite mounds and tropical soils

In this study, we test the use of the RAPD (Random Amplified Polymorphic DNA) molecular markers as a way to estimate the similarity of the microbial communities in various termite mounds and soils. In tropical ecosystems, termite activities induce changes in the chemical and physical properties of soil. The question then arises as to whether or not termites affect the presence of natural microbial communities. Successful 16S rDNA amplifications provided evidence of the occurrence of bacterial DNA in termite constructions including both soil feeder and fungus grower materials. A phenetic dendrogram using the similarity distance calculated from pairwise data including 88 polymorphic RAPD markers was reconstructed and bootstrap scores mapped. The microbial communities of the mounds of the four soil-feeding termites were clustered in the same clade, while those of the mounds of the fungus-growing species were distinct like those of control soils. Microbial changes in nests result from termite building behavior, depending on whether they include feces in their constructions for soil-feeders or use saliva as particle cement for fungus-growers. It is argued that RAPDs are useful markers to detect differences in microbial community structure not only between termitaries and control soils but also between mounds of soil-feeders.     

Exploring soil microbial communities and soil organic matter: Variability and interactions in arable soils under minimum tillage practice

This study describes an integrated approach (1) to monitor the quantity and quality of water extractable organic matter (WEOM) and size, structure and function of microbial communities in space (depth) and time, and (2) to explore the relationships among the measured properties. The study site was an arable field in Southern Germany under integrated farming management including reduced tillage. Samples of this Eutric Cambisol soil were taken in July 2001, October 2001, April 2002 and July 2002 and separated into three depths according to the soil profile (0–10 cm, 10–28 cm and 28–40 cm). For each sample, the quantity and quality (humification index, HIX) of water extractable organic matter (WEOM) were measured concomitantly with soil enzyme activities (alkaline phosphatase, β-glucosidase, protease) and microbial community size (C_mic). Furthermore, microbial community structure was characterised based on the fingerprints of nucleic acids (DNA) as well as phospholipid fatty acids (PLFA). We observed strong influences of sampling date and depth on the measured parameters, with depth accounting for more of the observed variability than date. Increasing depth resulted in decreases in all parameters, while seasonal effects differed among variants. Principal component (PC) analysis revealed that both DNA and PLFA fingerprints differentiated among microbial communities from different depths, and to a smaller extent, sampling dates. The majority of the 10 PLFAs contributing most to PC 1 were specific for anaerobes. Enzyme activities were strongly related to C_mic, which was depending on water extractable organic carbon and nitrogen (WEOC and WEON) but not to HIX. HIX and WEOM interact with the microbial community, illustrated by (1) the correlation with the number of PLFA peaks (community richness), and (2) the correlations with community PC analysis scores.     

Assessment of the microbial biomass using the content of phospholipids in soils of the dry steppe

Microbiological and biochemical investigations of chestnut soils and solonetzes were conducted in the dry steppe of the southern Privolzhskaya and northern Ergeni uplands. The living biomass of the microbial communities in the soils was estimated based on the content of phospholipids in the soils. Significant correlations were revealed between the contents of phospholipids and the main soil properties (the contents of humus, r = 0.66, P = 0.999; clay, r = −0.41, P = 0.95; physical clay, r = −0.57, P = 0.99; and pH, r = −0.59, P = 0.99). The content of phospholipids varied from 69 to 192 nmol/g of soil in the A1 horizons; with depth it decreased down to 36–135 in the B1 horizon and to 26–79 nmol/g of soil in the B2 horizon. The microbial biomass in the solonetzes was lower by 5 to 38% than that in the chestnut soils. A trend of the decreasing of the microbial biomass in the soils from the north to the south was revealed. Based on the content of phospholipids, the number of living microbial cells was assessed; the weighed averages of their number varied from 0.7–3.2 × 10¹⁰ to 7.5–13.6 × 10¹⁰.     

Labile pools of organic matter and microbial biomass in the surface soils under shifting cultivation in northern Thailand

In order to analyze the N mineralization process under shifting cultivation in northern Thailand, labile pools of soil organic matter were studied, which were considered to be the factors contributing to the N mineralization process. Organic C, (organic + NH₄ ⁺)-N, and hexose-C were extracted from fresh soils in the surface 0–5 cm layers with a 0.5 M K₂S₀. solution at 110°C in an autoclave (fraction A) or at room temperature with a reciprocal shaker (fraction B), and analyzed as labile pools of organic matter. In the traditional shifting cultivation system, the content of organic C in fraction A in the fallow fields for 8 to 15 y was 3,710 mg kg^-1 while that in the fallow fields for 1 y and 3 to 5 y was 2,640 and 2,600 mg kg^-1, respectively. A high correlation was observed between the contents of the labile pool in fraction A and total soil organic matter. The ratio of the pool in fraction A to total soil organic matter apparently remained constant through the input-output balance in the pool. The content of the labile pool in fraction B was the highest among the fields cultivated for 1 y after the slash and burn practice and it decreased in the course of the fallow period. The content of organic C was 548 mg kg^-1 in the fields cultivated for 1 y and 235 mg kg^-1 in the fallow fields for 8-15 y, respectively. There was a reverse relation between the contents of the pool in fraction B and microbial biomass. Therefore, the origin of the pool in fraction B was attributed to the microbial debris associated mainly with a decrease in the soil moisture content in the dry season. On the other hand, in the relatively intensive cultivation system, there was no significant difference in the contents of the labile pools both in fractions A and B among the land use stages, suggesting that the preservation mechanism of these pools, which was observed in the traditional cultivation system, did not operate well in the intensive system. In alternative farming systems in future, it will be essential to apply organic materials to soils to supply organic matter and to maintain the microbial biomass.