Oceanic structures of the Earth and the North Depression of Mars: A comparison of the formation mechanisms

The system of contemporary oceans on Earth and the North Depression of Mars are quasi-symmetrical in reference to the centers of of the hemispheres. Both systems had been formed over the common megacycle of evolution of planets and their origin is likely to have similar features. The formation of the Earth's oceanic system within the South Hemisphere seems to have proceeded in three stages: (1) the formation of a network of passive rifts at the center of the Gondwana; (2) the formation of the system of active rifts at the zones of forthcoming spreading; and (3) the spreading of the oceanic crust. The formation of the Mar's North Depression seems to have proceeded in two stages: (1) a formation of a dense network of grabens and faults at the center of the North Hemisphere over the upper mantle zone characterized by an anomalous warm-up and a density decrease; and (2) a collapse of the ancient crust and it's overflowing by basalts. The first stage of the ocean formation on Earth and Mars is similar. But there seems to have been a thinner lithosphere on Mars. The dense areal rifting was immediately followed by a total collapse

On the differences in continental rifting at the Earth, Mars and Venus

During the process of continental rifting on Earth, the lower ductile crust stretches, forming a neck, while the upper brittle crust is broken in blocks by faults, and the blocks sink down the thinned lower crust; if the stretching continues, the neck may break and a newly originated oceanic crust is formed at this place. The rift system structure depends on the depth of the boundary surface between the brittle crust and the ductile crust, the litospheric thickness, the tension value, etc.. The rigid brittle rifting when narrow necks form in the lower crust is characteristic of the contemporary Earth; on Mars the brittle rifting with large subsidence was characteristic of the Tharsis upland formation epoch. The ductile rifting is typical of the Venus. The differences in rheologic features of the lithospheres of different planets causes the variation in types of rifting

Changes in hydrophobic-hydrophilic properties of chernozems under the influence of mineral fertilizers and their aftereffect

Soil samples and granulodensimetric fractions isolated from them ((silt particle size less than 1 µm, light fraction (LF) with a density of less than 2 g/cm3 and a fraction of the residues) of ordinary chernozem from experimental fields of the Kamennaya Steppe agricultural landscape of the Voronezh region were studied. The main differences between the variants of the experiment are introducing or stopping mineral fertilizers, and in the aftereffect of irrigation (13 years). There is an increase in the content of LF when using mineral fertilizers, as well as a change in the composition of sizedensity fractionations, expressed in different content of C and N and hydrophobic-hydrophilic components of humus substances (HS) of soils, silt and LF. The irrigation had practically no effect on the hydrophobichydrophilic composition of the initial soils, while the relative content of the hydrophilic components of the silt fraction of the soil increased, and the hydrophilic composition of HS LF decreased. The use of mineral fertilizers led to a significant variation in the degree of hydrophilicity of HS in silt and LF with a smaller change of this indicator for the HS of the soil as a whole. The abolition of fertilizers application, on the contrary, affected the hydrophobichydrophilic composition of the soil as a whole, and the composition of the soil silt and LF. The increase in the proportion of hydrophilic components in the composition of soil HS, as well as in the composition of HS silt and LF occurred simultaneously with an increase in the hydrophobicity of the surface of the solid phase of soil and with an increase in the carbon content in the soil, which indicates the stability of the system as a whole. Since the physical fractions of soils reacted more intensively to changes in the agrogenic load, compared with native soil samples, and changes in their qualitative composition were traced in two versions of the experiment, monitoring of hydrophobic-hydrophilic components of soil and soil granulodensimetric fractions is advisable to monitor and diagnose soil changes during agricultural use

Changes in the hydrophobic-hydrophilic properties of the organic matter of the chernozems of the Kamennaya Steppe

Soil samples and physical size-density fractions isolated from them (silt particle size less than 1 µm, light fraction (LF) with a density of less than 2 g/cm3 and a fraction of the residue) of ordinary chernozem were studied in three contrasting variants of the experimental fields of the Kamennaya Steppe agrolandscape of the Voronezh region: mowed steppe, long-term permanent bare fallow and permanent corn – the main differences of which are in tillage (cultivated and not cultivated lands) and in the supply/absence of plant residues and root secretions. The LF content changes in the series: “mowed steppe” > “permanent corn” > “permanent bare fallow”, which corresponds to the direction of changes in the total carbon content of the soil and a decrease in the value of the contact angle of wetting (CA) of the surface of the solid phase of the studied chernozems. The determination of the total C and N content revealed the change in the qualitative and quantitative composition of the size-density fractions for different land use cases. Chromatographic fractionation of alkaline extractions of humus substances (HS) of chernozem samples and size-density fractions revealed an increase in the degree of hydrophilicity of HS while simultaneously increasing the hydrophobicity of the solid phase surface and the carbon content in the soil. HS of LF of the “mowed steppe” turned out to be by 63% more hydrophilic than HS of LF of “permanent bare fallow” and by 47% more hydrophilic than HS of LF of “permanent corn”. While the hydrophilicity of the HS silt differed by 16 and 27%, respectively. The hydrophilicity of the HS of the original soil in the plot of the “mowed steppe” was by 41% higher than the hydrophilicity of the HS in the soil in the plot of “permanent bare fallow” and by 24% higher than in the soil of the plot of “permanent corn”. In addition, changes in the hydrophilicity of HS of size-density fractions are more intense than the HS of the soil, so the change in the degree of hydrophilicity of HS of size-density fractions is an indicator of soil degradation under different agrogenic pressue

Methods for determining the organic carbon content in soils (critical review)

The paper presents theoretical basis of the methods for determining the content of soil organic carbon (SOC) both by direct dry combustion using automated analyzers and indirectly – by I.V. Tyurin and Walkley–Black oxidation. Author's and literature experimental data of SOC analyses in various soils by these methods are presented. Comparative analysis of the above data showed that in some cases the content of SOC determined by oxidability is lower than the one obtained by dry combustion (in most cases), while in others, on the contrary, the content of SOC is higher. This conclusion fully complies with the theoretical views of I.V. Tyurin on the chemical nature of soil organic matter (SOM). A schematic description of determining the content of total (organic) carbon in non-carbonate soils by dry combustion method using automated analyzers Leco (USA) and AH-7529 (Gomel, Belarus) is given. It was pointed out that it is difficult to determine SOC content by dry combustion method with automated analyzers in carbonate soils. For these soils it is recommended to determine the content of inorganic carbon by decomposition of carbonates with HClO4 solution using express analyzer AN-7529. The direct method of determining the content of SOC has the best metrological characteristics compared to ones of the indirect method, which convincingly confirms the authoritative opinions of Schollenberg and Tyurin about the inaccuracy of the latter. It is concluded that the indicators determined by the methods of Tyurin and Walkley–Black and dry combustion are chemically independent, characterizing, respectively, the oxidability and organic carbon content of SOM. It is recommended to use dry combustion method with automated analyzers when monitoring the content and stocks of organic carbon in soils

The contact angle of wetting as an integral indicator of physical-chemical properties of Сhernozems of Kamennaya Steppe

The sessile drop method was used to measure the contact angle of wetting (CA) of ordinary Chernozem from the fields of the Kamennaya Steppe agrolandscape used in various ways. The treatments differ in the intensity of tillage operations (protected mowed steppe, arable land after moldboard plowing), the use of mineral fertilizers and their aftereffect, as well as changes in soil properties under the influence of irrigation. At the same time, the total organic carbon content, C/N ratio, specific surface area, and rheological parameters were determined for the physical and chemical characteristics of soils. The results of the study showed that the hydrophilic-hydrophobic properties of the surface of the solid phase of soils, which largely determine the main structure-forming properties of soils, can be characterized by the value of the wetting edge angle. The CA of the studied soil samples varies from 32 degrees (highest wettability) to 45 degrees (lowest wettability). The lowest wettability is due to the increased content of hydrophobic compounds in the organic matter of soils and is characterized by the highest CA and is typical for native, untreated soil of the mowed steppe, which differs from other studied variants of the experiment in all explored physical and chemical parameters. Moldboard plowing as well as fallowing lead to changes in the physical and chemical properties of the soil and the qualitative composition of organic matter in the direction of their deterioration and a decrease in the CA. The use of mineral fertilizers contributes to the increase in the studied indicator mainly due to changes in plant productivity, in particular, the differences in CA are due to the impact of root secretions and plant residues on the soil properties. For the studied soils, the CA changes in the following series: mowed steppe > arable land with the mineral fertilizers application > arable land undergone the aftereffect of fertilizers. Correlation analysis revealed the relationship of CA with organic carbon content, specific surface area, and rheological characteristics of Chernozems. Thus, CA can serve as an integral indicator of changes in the physical and chemical properties of soils, their degradation changes under the conditions of different agricultural load. The method used in this research for determining CA requires a smaller amount of sample compared to rheological methods and is generally more informative than determining the content of organic matter

THE METHOD OF PREPARING SOIL SAMPLES FOR SOIL – WATER CONTACT ANGLE MEASUREMENT USING SESSILE-DROP TECHNIQUE

The method of soil samples preparation for measuring the (wetting) contact angle (CA) of the soil solid phase surface using membrane filters is proposed. The samples of kaolinite, a standard sample of chernozem and samples of agro-chestnut soil were taken for the experiment. The results of the CA measurements using two types of sample preparation for the analysis were compared. The first method of sample preparation was to apply a sample to a double-sided adhesive tape; the second method involved the deposition of suspensions of the studied samples of certain concentrations on membrane filters. The advantages and disadvantages of each sample preparation method are described. The significant difference in the obtained CA values depending on the sample preparation for measurement was revealed. The method of sample preparation with the use of membrane filters developed by the authors made it possible to reduce the CA measurement error by more than 2 times. Reducing the variation of the CA value of a single sample will allow comparing similar soil samples, including soils of the same type, but involved in different land use systems

Trehalose matrix effects on electron transfer in Mn-depleted protein-pigment complexes of Photosystem II

The kinetics of flash-induced re-reduction of the Photosystem II (PS II) primary electron donor P-680 was studied in solution and in trehalose glassy matrices at different relative humidity. In solution, and in the re-dissolved glass, kinetics were dominated by two fast components with lifetimes in the range of 2-7 microsec, which accounted for >85% of the decay. These components were ascribed to the direct electron transfer from the redox-active tyrosine YZ to P680+. The minor slower components were due to charge recombination between the primary plastoquinone acceptor QA- and P680+. Incorporation of the PS II complex into the trehalose glassy matrix and its successive dehydration caused a progressive increase in the lifetime of all kinetic phases, accompanied by an increase of the amplitudes of the slower phases at the expense of the faster phases. At 63% relative humidity the fast components contribution dropped to similar to 50%. A further dehydration of the trehalose glass did not change the lifetimes and contribution of the kinetic components. This effect was ascribed to the decrease of conformational mobility of the protein domain between YZ and P-680, which resulted in the inhibition of YZ -> P680+ electron transfer in about half of the PS II population, wherein the recombination between QA- and P680+ occurred. The data indicate that PS II binds a larger number of water molecules as compared to PS I complexes. We conclude that our data disprove the "water replacement" hypothesis of trehalose matrix biopreservation