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We investigated the effects of several tree species on dehydrogenase and urease activities in soils derived from two different parent materials (glaciofluvial sand and loess) in forested areas in southern Poland. We hypothesized that coniferous forests (pine, spruce) alter the soil cation exchange capacity (CEC) and decrease soil pH and, therefore, might decrease soil enzyme activities compared with broadleaf species growing on similar soils. Eight paired plots (12 · 12 m) were established on glaciofluvial sand in pine (Pinus sylvestris) + oak (Quercus robur) and spruce (Picea abies) + pine stands, as well as on loess-derived soils: beech (Fagus sylvatica) + pine and hornbeam (Carpinus betulus) + pine stands. Each plot was a 4 · 4 m grid with 16 sampling points. In soil samples pH, soil texture, and organic carbon, nitrogen, base cation contents, dehydrogenase and urease activities were determined. On both parent materials, the soil pH was lower under coniferous species than under broadleaf species. The acidifying effect of tree species on sandy soil was in the order of spruce = pine > oak, while that on loess was pine > beech > hornbeam. Hornbeam and oak increased the soil pH and stimulated enzyme activity in the soil. The content of fine fraction enhanced potential enzyme activities in soils, thus the loess soils had greater dehydrogenase and urease activity. The results suggest that pine stores more soil organic C in association with silt increasing the pool of stabilized soil organic C.

Forestry works using chainsaws result in up to 7 million liters of various mineral oils being soaked annually into forest soils. These substances, containing a complex mixture of polycyclic aromatic hydrocarbons (PAHs), are highly toxic. The aim of the study was to determine the effect of oil contamination with PAHs on the physical and biological properties of forest soils. The study area was located in southern Poland in the Miechów forest district. The experiment was conducted on four treatment blocks with various amounts of oil addition. The study included the determination of PAH content, dehydrogenase and urease activity, and biomass of earthworms. Physical properties were determined using the dryer method and Kopecky rings of 250 cm3 volume. The results obtained confirmed the hypothesis that oil contamination with PAHs modified the physical properties of forest soils and oil had a negative impact on enzyme activity in soil. Enzyme activity in the studied soils was negatively correlated with PAH content. Earthworm population density reflected the contamination level of oil-contaminated soils.

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In the Seyfert galaxy NGC 1566 and quasars 3C 345, 3C 446 long term (∼ 103 days) variations have been observed. We propose to explain them as a limit cycle behaviour, similar to that well studied in the case of dwarf novae outbursts. The key element of our analysis is the relationship between the accretion rate · and the surface density Σ.

The LIGO/Virgo gravitational-wave observatories have detected at least 50 double black hole (BH) coalescences. This sample is large enough to have allowed several recent studies to draw conclusions about the implied branching ratios between isolated binaries versus dense stellar clusters as the origin of double BHs. It has also led to the exciting suggestion that the population is highly likely to contain primordial BHs. Here we demonstrate that such conclusions cannot yet be robust because of the large current uncertainties in several key aspects of binary stellar evolution. These include the development and survival of a common envelope, the mass and angular-momentum loss during binary interactions, mixing in stellar interiors, pair-instability mass loss, and supernova outbursts. Using standard tools such as the rapid population synthesis codes StarTrack and COMPAS and the detailed stellar evolution code MESA, we examine as a case study the possible future evolution of Melnick 34, the most massive known binary star system (with initial component masses of 144 M ⊙ and 131 M ⊙). We show that, despite its fairly well-known orbital architecture, various assumptions regarding stellar and binary physics predict a wide variety of outcomes: from a close BH–BH binary (which would lead to a potentially detectable coalescence), through a wide BH–BH binary (which might be seen in microlensing observations), or a Thorne–Żytkow object, to a complete disruption of both objects by a pair-instability supernova. Thus, because the future of massive binaries is inherently uncertain, sound predictions about the properties of BH–BH systems formed in the isolated binary evolution scenario are highly challenging at this time. Consequently, it is premature to draw conclusions about the formation channel branching ratios that involve isolated binary evolution for the LIGO/Virgo BH–BH merger population.

The aim of the study was to determine the degree of soil pollution in different forest types around Krakow, using biochemical, chemical and magnetic methods. In assessing the degree of soil contamination, the impact of the forest species composition by comparing the surfaces of broadleaf and coniferous forest stands was taken into account. Enzymatic activity was related to other measures of pollution, i.e., heavy metal concentration, content of polycyclic aromatic hydrocarbons and level of magnetic susceptibility. The study was conducted in southern Poland. Krakow was the central point around which the test surfaces were designated. In soil samples pH, soil texture and organic carbon, nitrogen, base cation contents, dehydrogenase and urease activities were determined. Additionally, heavy metal concentration, polycyclic aromatic hydrocarbons (PAHs) content and magnetic susceptibility were recorded. The obtained results confirm the high diversity of forest soil pollution around Krakow agglomeration. Significant differences in both the content of heavy metals, polycyclic aromatic hydrocarbons and values of the magnetic susceptibility were observed in the soils of forest complexes located in different directions away from Krakow and at various distances from Krakow. The level of contamination is related to the historical and current deposition of industrial and urban dusts from Krakow and Silesia. The type of stand had a considerable influence on the content of polycyclic aromatic hydrocarbons. A higher content of aromatic hydrocarbons was observed in the soils of deciduous stands. A high level of magnetic susceptibility was observed in the soils of coniferous stands. The differences in enzymatic activity between the research plots result from different contents of PAHs and different amount of soil organic matter resulting from the species composition.