Characteristics of bacteria in the forest soils under natural vegetation

Characteristics of the predominant bacteria isolated in November and May from the forest soils of both dry and wet types under natural vegetation were studied.

Although Gram-negative rods were the most abundant bacteria in both soil types and in both seasons, their contents were less and other bacteria especially spore-forming ones increased in May.

Among Gram-negative rods in the soil of the dry type in November, the most predominant was those with nonchromogenic rods motile with polar flagella which grew in a simple synthetic media containing glucose or p-hydroxybenzoate and ammonium as the sole carbon and nitrogen sources. In May, the ratio of the bacteria which require amino nitrogen or those with more chomplex nutritional requirement increased. In the soil of moderately wet type, the difference in kinds of bacteria between the two seasons was not so clear as that in the dry type.

Most of Bacillus species obtained in these soils were those requiring amino acids or other growth factors among which B. cereus was most abundant.     

Changes in the temperature regime of podzolic soils in the course of natural forest restoration after clearcutting

The results of temperature monitoring in podzolic soils under the middle-taiga bilberry spruce forest and secondary mixed forest of the Komi Republic performed in 2008–2014 are presented. The changes in characteristics of soil temperature in the litter horizon and in the mineral horizons at the depths of 20 and 50 cm are outlined. It is shown that soil temperature regimes differ under the native spruce forest, young growth, and middle-aged secondary mixed forest. The soils of secondary phytocenoses are warmed up to a greater depth and are characterized by the higher heat supply. The differences are seen in a number of temperature parameters, such as the accumulated temperatures above 5°C and above 10°C at the depths of 20 and 50 cm. The most significant differences between the studied plots manifest themselves in the values of temperature amplitudes during the warm season. Maximum values of daily temperature amplitudes were obtained on the plot under young growth, whereas the soil under the middle-aged mixed forest was characterized by minimum values of daily temperature amplitudes.     

Effects of vegetation regime on denitrification potential in two tropical volcanic soils

Effects of vegetation and nutrient availability on potentail denitrification rates were studied in two volcanic, alluvial-terrace soils in lowland Costa Rica that differ greatly in weathering stage and thus in availability of P and base cations. Potential denitrification rates were significantly higher in plots where vegetation had been left undisturbed than in plots where all vegetation had been removed continuously, and were higher on the less fertile of the two soils. The potential denitrification rates were correlated strongly with respiration rates, levels of mineralizable N, microbial biomass, and moisture content, and moderately well with concentrations of extractable NH _inf4 ^sup+ , Kjeldahl N, and total C. In all plots, denitrification rates were stimulated by the removal of O₂ and by the addition of glucose but not by the addition of water or NO _inf3 ^sup- .This is Paper 2772 of the Forest Research Laboratory, Oregon State University     

Carbon storage and other properties of soils under agriculture and natural vegetation in São Paulo State, Brazil

Abstract. Topsoil (0–20 cm) and subsoil (60–100 cm) properties are compared at agricultural and nearby natural vegetation sites in São Paulo State. Differences are related to land use and climate, in order to estimate soil carbon storage under various ecosystems and also to study the effects of high-input agriculture on the chemical composition of soils with low activity clays. Within each land use, organic carbon in the topsoil is most strongly related to clay + silt content. This relationship is stronger for cropped, short savannah (cerrado) and tall savannah (cerradão) sites than for semi-deciduous and evergreen forest sites. Losses of topsoil carbon with cropping can be predicted if the initial carbon and the clay+silt contents are known. The greatest carbon losses after long term cultivation occurred in forest mineral topsoils, ranging from 6% for perudic clayey soils to 37% for ustic sandy soils. No significant difference in carbon content was found between the paired savannah-cultivated sites. In most of the originally less fertile soils cation exchange capacity was greater in the cultivated topsoil (Ap) than in the topsoil under savannah or forest (A1), probably because of liming and phosphate fertilization. Most subsoils at agricultural sites show increases in exchangeable bases (mainly Ca) and base saturation, but no significant change in pH.     

Pyrogenic transformation of tundra soils: Laboratory simulation

Pyrogenic losses of carbon and nitrogen from the surface horizons of soils in shrub ecosystems of mountain tundra, which are the most affected by fires in natural environments, have been estimated in laboratory simulation tests. The specific features of pyrogenic transformation of the physical and chemical properties and microbiological processes after exposure to high temperatures simulating the effect of fires of different intensity have been identified. Pyrogenic nature of the impact depends not only on the intensity of a fire, but also on the soil type. Its impact on tundra soils leads only to short-term increases in CO₂ emissions due to the destruction of pyrogenic organic compounds. A high level of fire impact leads to a significant reduction in microbiological processes in soils and shows no trend toward recovery in the long term, even under optimal conditions.     

Psychrotolerant actinomycetes in soils of the tundra and northern taiga

Actinomycetes adapted to low-temperature conditions are present in the cold soils of the tundra and northern taiga in quantities comparable to mesophylic forms and dominate in the soil actinomycete complex. Actinomycetes isolated from cold soils were identified as Streptomyces. Most actinomycetes relate to psychrotolerant forms according to habitation temperature. Two of them are conditionally psychrophilic. Specific properties of the investigated populations were identified by multirespirometrical testing.     

Psychrotolerant actinomycetes of plants and organic horizons in tundra and taiga soils

It has been revealed that in organic horizons and plants of the tundra and taiga ecosystems under low temperatures, actinomycetal complexes form. The population density of psychrotolerant actinomycetes in organic horizons and plants reaches tens and hundreds of thousands CFU/g of substrate or soil, and decreases in the sequence litters > plants > soils > undecomposed plant remains > moss growths. The mycelium length of psychrotolerant actinomycetes reaches 220 m/g of substrate. Application of the FISH method has demonstrated that metabolically active psychrotolerant bacteria of the phylum Actinobacteria constitute 30% of all metabolically active psychrotolerant representatives of the Bacterià domain of the prokaryotic microbial community of soils and plants. Psychrotolerant actinomycetes in tundra and taiga ecosystems possess antimicrobial properties.     

Accumulation of polycyclic aromatic hydrocarbons in soils and plants of the tundra zone under the impact of coal-mining industry

Thirteen polycyclic aromatic hydrocarbon (PAH) compounds were identified in organic horizons of tundra surface-gleyed soils ( Histic Stagnosols (Gelistagnic) and plants. The total content of PAHs in contaminated soils exceeded the background values by three times. Concentrations of low-molecular weight hydrocarbons in soils at different distances from the coalmines were relatively stable. Concentrations of highmolecular weight hydrocarbons had a distinct maximum at a distance of about 0.5 km from the source of emission. The increased values of correlation coefficients were found between PAH concentrations in organic soil horizons, plants, and coal of the Vorkutinskaya mine. Mostly low-molecular weight structures predominated in the organic soil horizons and in the studied plant species. The maximum capacity for the biological accumulation of PAHs was displayed by Pleurozium schreberi and the minimum capacity was displayed by Vaccinium myrtillus. Mosses and lichens actively absorbed polyarenes from the surface; most of the PAHs were transported into the plants. This phenomenon was not observed for Vaccinium myrtillus Concentrations of PAHs on the surface and in plant tissues decreased with an increase in the distance from the mine. Distribution of polyarenes in plant organs was nonuniform. Insignificant excess of concentration of polyarenes was found in dead part of Pleurozium schreberi in comparison with its living part. The accumulation of polyarenes in the leaves of Vaccinium myrtillus was higher than that in its stems and roots.     

Freeze-thaw regime effects on carbon and nitrogen dynamics in sub-arctic heath tundra mesocosms

Freeze-thaw fluctuations in soil temperature may be critical events in the annual pattern of nutrient mobilisation that supplies plant growth requirements in some temperate, and most high latitude and high altitude ecosystems. We investigated the effects of two differing freeze-thaw regimes, each of which is realistic of in situ spatial and temporal variation in field conditions, on C and N dynamics in sub-arctic heath tundra mesocosms. In addition, ¹⁵N isotopic label was used to follow the partitioning of a labile N pool between major ecosystem components, both during the freeze-thaw treatments phase, and in a subsequent equilibration phase. A single deep freeze treatment phase enhanced dissolved total and labelled N pools in the soil solution at initial thaw, and resulted in reduced pool sizes at the end of the equilibration phase. By contrast, a multiple freeze-thaw cycling treatment directly enhanced the dissolved labelled N pool, but did not significantly affect dissolved total N. Furthermore, both dissolved labelled N and dissolved total N pools were significantly enhanced in the equilibration period following multiple freeze-thaw, the latter due to a marked increase in soil solution NH₄⁺. Microbial biomass C was not significantly affected by either of the freezing treatments upon final thaw, but was significantly reduced over the combined treatment and equilibration phases of the multiple freeze-thaw regimes. Furthermore, the treatments had no significant effects on total or labelled N within the microbial biomass over either phase. Total mesocosm CO₂ efflux rates remained closely correlated with soil temperature throughout the experiment in both regimes, suggesting that respiratory flushes associated with treatment-induced microbial cell lysis were negligible. Together, these results indicate that moderate freeze-thaw fluctuations may have minimal influences on microbial biomass pools, but nevertheless can have strong contrasting effects on the amounts, forms, and timing of N and organic C supply into the soil solution. Ecosystem losses via N₂O effluxes were of greatest magnitude immediately upon thawing in both treatments, and were of similar total magnitude to inorganic N leachates in throughflow. Herb leaves, total fine roots, and vascular stems accumulated some ¹⁵N label in one or both of the freezing treatments by the end of the experiment. Together, these results indicating very small N losses relative to the magnitudes of internal transfers, suggest tight ecosystem N cycling both during and after freeze-thaw events. Furthermore, our small and subtle effects on microbial and soluble C and N pools relative to previous studies using more severe regimes, suggests that periods of moderate freeze-thaw fluctuations may have only a minor influence on the annual pattern of C and nutrient dynamics in seasonally cold ecosystems.     

Features of cryogenic environment in soils of continental tundra and arid steppe on the southern Khangai slope under electron microscope

Morphoscopic studies were conducted with the aid of SEM and TEM microscopes, on quartz grains and fractions not exceeding 2 μm, on soil samples from the continental tundra, alpine meadow and arid steppe. The aim of these studies was to define the features and properties of the quartz grains and fractions, produced by the environment of the cryoarid continental climate of Central Asia. It has been established that in cold and humid climates processes of cryogenic and hydrothermic splitting occur on the surface of quartz grains and in cold and dry climates processes of cryothermic scalling. The increase in the surface area of disintegrated minerals under continental climate conditions is accompanied by cryochemical coating by mineral-organic compounds.     

城市化进程中撂荒地植被恢复方式对植物多样性的影响

通过野外调查,研究鄱阳湖生态经济区城市化进程中农田生态系统撂荒后,自然更新和人工更新2种方式下的植物多样性和群落物种结构.结果表明：1）在撂荒地共发现42种植物,隶属22科42属,其中自然更新群落样地有10科20属,人工更新群落样地有19科34属;2）2个群落的科、属、种数在统计上差异不显著,只表现出人工更新群落稍高于自然更新群落,植物丰富度、多样性指数在统计上差异不显著,但是呈上升趋势;3）自然更新和人工更新2个群落间的植物种相似系数为0.44,自然更新和人工更新2个群落中的共有植物种类为12种,以一年生草本居多;4）应用除趋势对应分析排序方法（DCA）分析表明,2个群落结构间已形成梯度,在人工更新群落增加了多年生草本、多年生草质藤本和小灌木,人工更新减缓了植物多样性丧失的速度.在城市化圈地过程中,建议在撂荒期栽植乔木树种,有利于生物多样性的保护.     

Thermal diffusivity and temperature regime of soils in large lysimeters of the experimental soil station of Moscow State University

The thermal diffusivity of the upper horizons of model soddy-podzolic soils in the lysimeters depends on their water contents and varies within 2.1?4.32 × 10^?7 m²/s in the Ap horizon, 1.59?3.99 × 10^?7 m²/s in the B1 horizon, 1.28?3.74 × 10^?7 m²/s in the plowed B2 horizon, and 1.12?4.10 × 10^?7 m²/s in the B2 horizon. The dependence of the thermal diffusivity on the soil water content is described by an inverted parabolic curve for the Ap horizon, an S-shaped curve for the B1 and B2 horizons, and by a curve of transitional type for the plowed B2 horizon. The temperature regimes of model soils with different morphologies of the profile do not differ much and are close to the soil temperature regime under natural conditions on the plots of the weather station of Moscow State University.     

Effect of vegetation cover on the hydrology of reclaimed mining soils under Mediterranean-Continental climate

Vegetation cover plays a major role in the restoration and stabilization of disturbed systems. The analysis of relationships between restored vegetation and soil hydrology has special relevance for the evaluation and operation of mining reclamation, particularly in Mediterranean-Continental environments, where climatic conditions restrict the development of continuous vegetation cover. The effect of herbaceous vegetation cover on soil hydrology was analysed by means of rainfall simulation (63 mm h^− 1; 0.24 m²) in reclaimed soils derived from opencast coal mining (a non-saline and clay-loam textured spoil) in central-eastern Spain. A total of 75 simulation experiments were conducted at three different times throughout the year (late winter, summer and autumn) to control the influence of seasonal climatic fluctuations. Sediment concentrations in runoff and the runoff coefficient decreased exponentially with vegetation cover, while increases in steady infiltration rates were obtained with vegetation cover. Additional delays in runoff responses (longer time to runoff start and stabilization) and increases in the wetting front depth were observed with vegetation cover. Seasonal variations in soil surface state and moisture strongly influenced hydrological responses; although the influence of season on the analysed hydrological responses was attenuated by vegetation cover, especially in the case of infiltration rates. We also determined a practical ground cover threshold for site restoration and evaluation of over 50% vegetation cover, which could help achieve an optimum biological control of hydrological soil responses in the studied environment.     

Nitrogen regime of soils with different macrosymbiont genotypes

The specificity of the nitrogen regime in gray forest and meadow-chernozemic soils under the effect of different genotypes of peas (Pisum sativum L.) was shown under field and optimal hydrothermal conditions. The dynamics of the nitrogen form ratios in soils with and without symbiotic nitrogen fixation was studied. The role of the macrosymbiont type genotype in the accumulation of ammonium, nitrate, and microbial nitrogen in soils was revealed.     

Pyrogenic disturbances of the hydrothermic regime of cryogenic soils under light coniferous forests in southeastern Siberia

Pyrogenic transformations of the physical state of cryogenic soils in the southern and middle taiga were investigated. The long-term dynamics of the microclimate on burns and the soil temperature and moisture to the depth of 120 cm were studied. Data on the postfire restoration of the ground cover are presented. Experiments on artificial sprinkling of burned areas differing in the degree of the burning out of the forest litter, the slope gradient, etc., have been performed. An experimental model demonstrating the relationships between the surface runoff and five environmental factors has been proposed. The pyrogenic destruction of the ground cover and the lower phytocenosis layers was accompanied by significant disturbances of the microclimate and anomalous thawing of the permafrost on the burns. In the pine stand on the colluvial fan after the intense fire, the soil temperature at the depth of 10 cm (in the summer) exceeded the control value by 3–5°C; in the larch forest on the southern slope of the Stanovoi Ridge, it increased by 1.5–2.0 times after the fire of medium intensity. On the mountain slopes, the surface runoff was significantly intensified, which resulted in drastic environmental and silvicultural consequences.     

Composition of humus in chronosequences of buried soils in the tundra zone

The humus characteristics in buried Holocene and Late Pleistocene paleosols of the tundra zone have been studied. It is shown that the paleosol sequences encompassing the time span from 55 to 2.5 ka BP contain paleosols with analogous types of humus, attesting to the cyclic repeatability of the corresponding stages of soil formation. A tendency for an increase in the degree of humification in the course of soil development has been revealed. Within the ultracontinental areas of East Siberia, the accumulation of salts accompanied soil formation in the Late Pleistocene and Holocene.     

Lessivage and its relation to the hydrological regime of soils

By the examples of four typical catenas in the East European Plain, the role of lessivage in the development of automorphic and hydromorphic loamy and clayey soils with light-colored acid eluvial horizons and with different degrees of gleyzation has been studied. It is found that characteristic features of lessivage are often observed in the soils without hydrological barriers hampering or preventing the vertical migration of soil water and mass transfer processes. The hydrological barriers may be represented by the shallow horizons of temporarily perched water, or by the ascending capillary fringe of the ground water, or by the water-saturated horizons, in which the volume of free pores does not exceed 2–4%. It is shown that light-colored acid eluvial horizons may be formed in the profiles of loamy and clayey soils without any signs of lessivage. The development of strongly gleyed soils (gleyed soddy-podzolic soils and pseudogley soils (Stagnosols)) is not related to colmatage (silting of their illuvial horizons through lessivage); it is conditioned by the actual hydrological regime of these soils. The role of lessivage, podzolization, and gleyzation in the development of clay-differentiated soils is discussed.     

Comparison of pyrites varying in water-soluble sulfur with gypsum for the reclamation of alkali soils under a rice-wheat rotation

We evaluated the effect of agricultural-grade (AG) pyrites (total sulfur 22%) varying in water-soluble sulfur (1–8%) and gypsum on the soil properties and yields of rice and wheat in alkali soils during the years 1993–1995 at the Gudha and Saraswati experimental farms at the Central Soil Salinity Research Institute, Karnal, India. Gypsum and pyrites were applied on the basis of gypsum requirement (GR) of the soils. Results showed that the efficiency of AG pyrites in decreasing soil pH and exchangeable sodium percentage (ESP) and increasing crop yields was dependent on their water-soluble sulfur content at the time of application to the field. Pyrites with 5.5% and 8% soluble sulfur were as effective as gypsum. The freshly mined pyrite (water-soluble S 1%) was found to be inefficient in reclaiming alkali soils. We also explored the possibility of increasing the water-soluble sulfur content of pyrite by optimizing its storage conditions. When pyrite (1% water-soluble S) was stored under moist conditions by sprinkling water over the bags under a rain shelter, there was an enrichment of indigenous iron- and sulfur-oxidizing bacteria of pyrite, and the water-soluble sulfur increased to 5% within a period of 6 months. However no such increase occurred when pyrite was stored dry. We conclude that the soluble sulfur content of pyrite increased during its storage under moist conditions and should be between 6% and 8% at the time of its application to the field.     

Experimentally substantiated equations of the interrelations between the agrochemical characteristics of tundra soils

The detailed analysis of the results obtained in the course of experimental studying of the tundra soils in Western and Central Siberia and in the European part of Russia has revealed the general regularities of the variability and the relationships between the agrochemical and other properties of the soils. On the basis of these data, the calculated methods for the assessment of a complex of agrochemical properties of natural and disturbed tundra soils under different moisture and thermal conditions were elaborated. Among the properties analyzed, the following are important for plant growth: the acidity and the content of humus, organic carbon, total nitrogen, mobile phosphorus, nitrogen, and potassium. The relationships between the soil agro-chemical properties and the plant productivity allowed applying them for the quantitative evaluation of the environmental threat of the soil-plant cover’s degradation because of different predominantly mechanical disturbances.     

Carbon in tundra soils in the Lake Labaz region of arctic Siberia

Large amounts of carbon are stored in permafrost‐affected soils of the Arctic tundra. The quantity, distribution and composition of this carbon are important, because much of the carbon is likely to be released as a result of global warming. We have studied soils of the central Siberian Arctic to determine the carbon content and the nature of the organic matter by density fractionation, and ¹³C‐NMR‐ and ¹³C‐stable‐isotope analyses. There are pronounced differences in the profile and variations from place to place in the quantity and nature of soil organic matter. We estimated that the mean stock of carbon was 14.5 kg m^–2 within the active layer. We found a total of about 30.7 kg C m^–3 in the entire upper metre of the soils. Carbon of the tussock tundra showed strong vertical differentiation, with a large proportion comprising decomposed, recalcitrant compounds. We identified within the soil several zones of aerobe and anaerobe decomposition. Mobile carbon fractions have precipitated under the influence of low temperatures.