University of Forestry
  • Sofia, Sofia-Capital, Bulgaria
Recent publications
We propose a microscopic model in order to investigate the multiferroic properties of CuBr2 in dependence on temperature, size, magnetic field and ion doping. Using a Green’s function technique we have calculated the magnetization, the heat capacity, the polarization and the dielectric constant. The specific heat has at the magnetic transition temperature TN a clear peak which disappears by applying an external magnetic field h. The polarization increases whereas the dielectric constant decreases with increasing h due to strong magnetoelectric coupling. In a CuBr2 nanoparticle appears a weak ferromagnetism due to the uncompensated spins on the surface. The magnetization increases with decreasing nanoparticle size. The Neel temperature rises strongly applying by ion doping a compressive strain and decreases by a tensile strain.
The European roe deer (Capreolus capreolus) is one of the most numerous and widespread ungulate species in Europe, which has complicated the assessment of its genetic diversity on a range-wide scale. In this study, we present the mitochondrial DNA control region (mtDNA CR) genetic diversity and population structure of roe deer in Europe based on the analyses of 3010 samples, which were described as European roe deer individuals. Our analyses revealed two main diversity hotspots, namely Eastern and Central Europe. We proposed that these hotspots result from the Siberian roe deer (C. pygargus) mtDNA introgression and the secondary contact of mtDNA clades, respectively. Significantly lower values of genetic diversity (nucleotide and haplotype diversity) were recorded in the peripheral areas of the species' range, including the southernmost parts of the Last Glacial Maximum (LGM) refugial areas. Roe deer population in Europe consists of 2-3 genetic groups according to SAMOVA, and 15-16 clusters identified by GENELAND. The main driver of roe deer population structure in the eastern parts of the continent has been introgression of mtDNA of C. pygargus. Spatial genetic analyses revealed a complex structure of roe deer on a pan-European scale, which presumably results from post-glacial recolonization of the continent from various parts of a large LGM refugial area by different roe deer mtDNA clades and haplogroups.
The current study aimed to determine the major and minor nutritional constituents of Sorbus domestica L. fruits. It was revealed that palmitic acid was the most commonly occurring saturated fatty acid, while linoleic acid represented the major polyunsaturated fatty acid. The sterol fraction consisted mainly of β-sitosterol. Small amounts of lipophilic pigments were quantified. Potassium, iron, and boron were the most abundant macro-, micro-, and ultra-trace elements. The amino acid composition analysis suggested that the non-essential amino acids predominated over the essential ones. Soluble sugars (fructose and glucose) represented a large part of the total carbohydrate content, but pectin formed the major part of polysaccharides. Malic acid was the most abundant organic acid whereas quercetin-3-β-glucoside, neochlorogenic, and 3,4-dihydroxybenzoic acids were the major phenolic constituents. Fruits exhibited free-radical scavenging and protecting ability against peroxyl and hydroxyl radicals. Service tree fruits provided valuable bioactive constituents having a high nutritional value and potential health benefits.
1. Riparian vegetation supports high biodiversity providing many services and is, therefore, an important landscape element. Riparian ecosystems are subject to numerous pressures leading to population decline and genetic erosion of riparian plants. This may have cascading effects at various ecosystem levels, including decreasing ecosystem services, so identifying the current status of genetic diversity of riparian tree species is vital to improve the effectiveness of restoration efforts. Journal of Applied Ecology 2. We aimed to elicit expert views on the status and importance of genetic diversity of tree species, and conservation needs across European riparian ecosystems. Sharing of such information among researchers, managers and policymakers has the potential to enhance ecological restoration and management of riparian ecosystems. 3. We identified experts in riparian genetic resources conservation and management across Europe. These included stakeholders with different perspectives, ranging from researchers to practitioners. We designed a set of questionnaires where our identified experts were asked to answer questions related to the status and conservation of genetic diversity of riparian tree species in their respective countries. Specifically, we asked about societal awareness, legislative tools, good practices and conservation or restoration projects accounting for intraspecific genetic diversity and differentiation of tree species in riparian ecosystems. Questionnaire responses were analyzed and discussed in light of the scientific literature to define needs and priorities related to the management and conservation of genetic diversity of riparian tree species. 4. The experts recognized that a combination of in situ and ex situ measures and/or integrative conservation of riparian ecosystems is the most appropriate option for conserving the genetic diversity of riparian tree species. Simultaneous application of conservation measures at the level of priority species, identified by experts, and protection of riparian areas are required. 5. Synthesis and applications. This study revealed the importance of recognizing the ecological processes that shape the genetic diversity of riparian tree species in hydrographic networks (dendritic spatial configuration, specific patterns of gene flow among riparian populations, fragmentation of river by dams) but also the need to overcome socioeconomic barriers, such as lack of policy priority, deficiency in funding and weak legislation framework.
The diet of the Common Barn-owl in a forest- and shrub-dominated hunting area in the Strandzha Mountains, southern Bulgaria, was identified from 516 prey specimens. Shrews (52.9% by number, 26.7% by biomass) and rodents (42.1% N, 71.5% B) were prevalent. Among them, White-toothed shrews, Crocidura sp., (45.3% N, 21.4% B) was the most numerous prey genus. Mice, Apodemus sp., (15.7% N, 29% B) contributed with the largest share to the food biomass due to high predation of Striped field mice, A. agrarius, (12.2% B). The proportions of forest species in diet (Apodemus sp, Sorex sp., and dormice Gliridae) increased with the higher proportion of forest habitats (forests and shrublands cover more than 25% of the area) in most Barn Owl hunting territories in southern Bulgaria.
The multiferroic properties of BiCrO3 (BCO) ‐ bulk and thin films ‐ are investigated for the first time using a microscopic model. The influence of ion doping on the multiferroic properties of BCO is also studied because the doping process changes the physical properties and can be used for potential applications in magnetoelectronic devices. The magnetization M increases by Mn and decreases by Ga ion doping whereas the Neel temperature TN decreases in both cases. There are some discrepancies by the polarization whether it is ferroelectric or antiferroelectric. We have shown that bulk pure BCO is antiferroelectric because the electric field dependence of the polarization P shows a double hysteresis loop and the dielectric constant has not anomalies at TN. In Ga, Mn or Ti doped BCO appears a ferroelectric polarization. The specific heat shows a peak at TN for BCO. By Ga doping this peak vanishes with increasing x. The multiferroic behavior of BCO is demonstrated in the magnetic field dependence of the dielectric constant. In BCO thin films is observed ferroelectric and ferromagnetic behavior. This article is protected by copyright. All rights reserved.
Citizen science plays an important role in the early detection of invasive alien species (IAS). The involvement of young people in initiatives related to citizen science in Bulgaria could contribute to better monitoring of IAS because of mobility and digital skills of those people. Based on a questionnaire survey, key aspects of involvement of young people in citizen science initiatives were analysed. Two groups of respondents, including professionals (with an educational background in biology or with professional activities related to the bioresources) and non-professionals (not connected with bioresources) were asked to make judgments about their own level of knowledge about: (1) IAS issues, (2) the level of awareness of citizen science; (3) the motivation and preferable ways to participate in citizen science; and (4) the most appropriate approaches for IAS awareness raising. A total of 337 young people in the age range of 15-30 years were questioned during the period 2019-2021. The results show that there is no significant difference between the responses of the two groups of respondents to the questionnaire - professionals and non-professionals. In both groups, less than 50% of respondents are aware of issues related to IAS. Less than 40% of respondents indicated the correct definition of citizen science. The leading motivation factor to participate in citizen science initiatives is “caring for nature” followed by “to contribute to nature conservation” and “to learn more about nature”. Most of the respondents are interested in additional information related to IAS and prefer online sources for information.
Lignins are the most important aromatic renewable natural resource today, serving as a sustainable, environmentally acceptable alternative feedstock to fossil-derived chemicals and polymers in a vast scope of value-added applications. Lignin is a biopolymeric molecule that, together with cellulose, is a fundamental component of higher vascular plants structural cell walls. It can be extracted from by-products of the pulp and paper industries, agricultural waste and residues, and biorefinery products. Lignin properties may vary depending on source and extraction method with carbon and aromatic as the main compositions in lignin structure. These rich compositions make lignin more valuable, allowing for the creation of high-value-added green composites. However, the complex structure of lignin creates low reactivity to interact with cross-linker, and hence chemical modification is substantial to overcome this problem. This review aimed to present and discuss lignin structure, variation of lignin chemical properties regarding its source and extraction process, recent advances in chemical modification of lignin to enhance its reactivity, and potential applications of modified lignin for manufacturing value-added biocomposites with enhanced properties and lower environmental impact, such as food handling/packaging, seed coating, automotive devices, 3D printing, rubber industry, and wood adhesives.
Nowadays, the increase in the wastewater generated from the mushroom cultivation sector has become a serious environmental pollution concern. Therefore, the present study aimed to assess the efficiency of two water ferns (Azolla pinnata and A. filiculoides) in phytoremediation of mushroom farm wastewater (MFW) under stagnant and flowing tank reactor systems. For this, the laboratory scale experiments were conducted using five treatments, i.e., control (absolute borewell water), S50 (15 L borewell water + 15 L MFW: stagnant mode), S100 (30 L MFW: stagnant mode), F50 (15 L borewell water + 15 L MFW: flowing mode), F100 (30 L MFW: flowing mode), separately for both Azolla spp. After 15 days, A. pinnata and A. filiculoides significantly (p < 0.05) reduced the physicochemical parameters of MFW such as pH (18.87 and 18.56%), electrical conductivity (EC: 80.28 and 78.83%), total dissolved solids (TDS: 87.12 and 86.63%), biochemical oxygen demand (BOD: 90.63 and 89.90%), chemical oxygen demand (COD: 86.14 and 85.54%), and total Kjeldahl’s nitrogen (TKN: 84.22 and 82.44%), respectively, in F100 treatment. Similarly, the highest growth and biochemical parameters of Azolla spp. were also observed while using absolute MFW treatment in a flowing tank reactor system. Moreover, out of the two tested growth kinetic models, the logistic model showed better fitness to the experimental data and prediction of critical growth parameters compared to the modified Gompertz model. The findings of this study are novel and suggest sustainable upcycling of MFW using plant-based treatment techniques with the production of high-quality Azolla spp. biomass.
Actinobacillus pleuropneumoniae (App) is the etiological agent of porcine pleuropneumonia. The purpose of the study was to present a serological report on App prevalence among pigs in industrial farms in Bulgaria. Seventy-two pigs from four industrial farms in four districts of Bulgaria – Eastern Bulgaria (Razgrad and Yambol districts) and Western Bulgaria (Lovech and Sofia districts) were included. Animals were divided in two age groups: weaners and fattening pigs. A commercial en-zyme-linked immunosorbent assay (ELISA, INgezim APP MIX, Eurofins Ingenasa, Madrid, Spain) for the detection of antibodies against App parasuis in porcine serum was used. Microtitr plate was coated with App antigen of the serovars 1, 2, 9 and 11. Positive results for anti-App antibodies were detected in 32 (44.4%) of all 72 tested sera. The overall seropositivity in weaners and fattening pigs was 22.2% (8/36), and 66.7% (24/36), respectively. The highest App seropositivity in pigs was found in Eastern Bulgaria – 61.1% (22/36; P<0.001) in comparison to App seropositivity in Western Bulgaria – 27.8% (10/36; P=0.137). This study on anti-App prevalence among pigs in Bulgaria gives new insights on App epidemiology in our country.
Sophora japonica is a source of several flavonol, flavone and isoflavone glycosides that are reported to positively affect menopausal symptoms including osteoporotic complications. In the present study fructus Sophorae extract (FSE) was administered orally for three months at a dose of 200 mg kg –1 in ovariectomized (OVX) New Zealand rabbits. 3D computed tomography scans and histopathological images revealed microstructural disturbances in the bones of the castrated animals. FSE recovered most of the affected parameters in bones in a manner similar to zoledronic acid (ZA) used as a positive control. The aglycones of the main active compounds of FSE, daidzin, and genistin, were docked into the alpha and beta estrogen receptors and stable complexes were found. The findings of this study provide an insight into the effects of FSE on bone tissue loss and suggest that it could be further developed as a potential candidate for the prevention of postmenopausal osteoporotic complications.
In the last decade, annona crop was introduced to Lebanon. Thisexperiment was conducted to enhance the adaptation of annona to localconditions. Three scion/rootstock combinations were obtained fromself– and cross– cleft grafting of Annona squamosa (Sq) and Annonacherimola (Ch), planted in calcareous “white soil” and clay–loamy “redsoil”, and fertilized or not by iron (Fe) through fertigation. In the third year,the treatment red soil–iron fertilization–Sq/Ch had significantly highest plant height, trunk diameter, leaf number, number of primary roots, fruitnumber and yield. In the third year, despite iron fertilization, plants of thethree graft combinations cultivated in red soil had higher flower number,fruit number, individual fruits weight and yield, than those planted in whitesoil. In the same year, iron fertilization in white soil had only affectedtotal dry mass, leaf mass fraction and leaf iron content. However, ironfertilization of Sq/Ch planted in red soil has improved leaf number,primary root number, primary root length, leaf chlorophyll index, andleaf iron content compared to non–fertilized plants. Conclusively, ironfertilization in red soil could be a useful method improving the performanceand yielding capacity of annona crop mainly in Sq/Ch combination.
Agro-wastes, such as crop residues, leaf litter, and sawdust, are major contributors to global greenhouse gas emissions, and consequently a major concern for climate change. Nowadays, mushroom cultivation has appeared as an emerging agribusiness that helps in the sustainable management of agro-wastes. However, partial utilization of agro-wastes by mushrooms results in the generation of a significant quantity of spent mushroom substrates (SMS) that have continued to become an environmental problem. In particular, Shiitake (Lentinula edodes Berk.) mushrooms can be grown on different types of agro-wastes and also generate a considerable amount of SMS. Therefore, this study investigates the biotransformation of SMS obtained after Shiitake mushroom cultivation into biogas and attendant utilization of slurry digestate (SD) in tomato (Solanum lycopersicum L.) crop fertilization. Biogas production experiments were conducted anaerobically using four treatments of SMS, i.e., 0% (control), 25, 50, and 75% inoculated with a proportional amount of cow dung (CD) as inoculum. The results on biogas production revealed that SMS 50% treatment yielded the highest biogas volume (8834 mL or 11.93 mL/g of organic carbon) and methane contents (61%) along with maximum reduction of physicochemical and proximate parameters of slurry. Furthermore, the biogas digestate from 50% treatment further helped to increase the seed germination (93.25%), seedling length (9.2 cm), seedling root length (4.19 cm), plant height (53.10 cm), chlorophyll content (3.38 mg/g), total yield (1.86 kg/plant), flavonoids (5.06 mg/g), phenolics (2.78 mg/g), and tannin (3.40 mg/g) contents of tomato significantly (p < 0.05) in the 10% loading rate. The findings of this study suggest sustainable upcycling of SMS inspired by a circular economy approach through synergistic production of bioenergy and secondary fruit crops, which could potentially contribute to minimize the carbon footprints of the mushroom production sector.
The purpose of this study was to prepare low viscosity lignin-based polyurethane (LPU) resins for the modification of ramie (Boehmeria nivea (L.) Gaudich) fiber via impregnation to improve the fi-ber’s thermal and mechanical properties. Low viscosity LPU resins were prepared by dissolving lignin in 20% NaOH and then adding polymeric 4,4-methane diphenyl diisocyanate (pMDI, 31% NCO) with a mole ratio of 0.3 NCO/OH. Ramie fiber was impregnated with LPU in a vacuum chamber equipped with a 2-stage vacuum pump. Several techniques such as Fourier-transform infrared (FTIR) spectroscopy, differential scanning calorimetry, thermogravimetric analysis, py-rolysis-gas chromatography-mass spectroscopy, and universal testing machine were used to characterize lignin, LPU, and ramie fiber. The LPU resins had low viscosity ranging from 77 to 317 mPa·s−1. According to FTIR analysis, urethane bonds were formed during the synthesis of LPU resins. After impregnation, the reaction between the LPU’s urethane group and the hydroxy group of ramie fiber increased thermal stability by an average of 6% and mechanical properties by an average of 100% compared to the untreated ramie fiber. The highest thermal stability and tensile strength were obtained at ramie impregnated with LPU-ethyl acetate for 30 min, with a residual weight of 22% and tensile strength of 648.7 MPa. This study showed that impregnation with LPU resins can enhance the thermal and mechanical properties of fibers and increase their wider in-dustrial utilization in value-added applications.
The sustainability, performance, and cost of production in the plywood industry depend on wood adhesives and the hot-pressing process. In this study, a cold-setting plywood adhesive was developed based on polyvinyl alcohol (PVOH), high-purity lignin, and hexamine. The influence of lignin content (10%, 15%, and 20%) and cold-pressing time (3, 6, 12, and 24 h) on cohesion, adhesion, and formaldehyde emission of plywood was investigated through physical, chemical, thermal, and mechanical analyses. The increased lignin addition level lowered the solids content which resulted in reduced average viscosity of the adhesive. As a result, the cohesion strength of the adhesive formulation with 10% lignin addition was greater than those of 15% and 20% lignin content. Markedly, the adhesive formulation containing 15% lignin addition level exhibited su-perior thermo-mechanical properties than the blends with 10% and 20% lignin content. This study showed that 10% and 15% lignin content in the adhesive resulted in better cohesion strength than that with 20% lignin content. However, statistical analysis revealed that the addition of 20% lignin in the adhesive and using cold-pressing time of 24 h could produce plywood that comparable to the control polyurethane resins, i.e. dry tensile shear strength (TSS) value of 0.95 MPa, modulus of rupture (MOR) ranging from 35.8 MPa, modulus of elasticity (MOE) values varying from 3980 MPa, and close-to-zero formaldehyde emission (FE) of 0.1 mg/L, which meets the strictest emission standards. This study demonstrated the feasibility of fabricating eco-friendly plywood bonded with PVOH-lignin-hexamine-based adhesive using cold pressing as an alternative to conventional plywood.
The purpose of the study was to measure the Brinell hardness (HB) of six wood species and evaluate the ability to recover the depth of the imprint (self-re-deformation). Straight-grain clear samples of ash, beech, alder, birch, iroko, and linden wood were prepared. Measurements were made in the three main reference timber cross-sections: radial (R), tangential (T), and axial/longitudinal (L) and with two measuring loads of 30 kG and 100 kG (294.2 N and 980.7 N). The tested wood species could be classified into hard (ash, beech), medium-hard (alder, birch, iroko), and soft (linden) wood species. The HBs of each tested wood species differed in the cross-sections, i.e., side hardness (R, T) and end hardness (L). Higher HB values were obtained at 100 kG load in all species and all three cross-sections. The lowest influence of the measurement force value on the HB value was revealed for the soft wood species (linden: 107–118%). This influence was visible for the other five medium-hard and hard wood species, ranging from 125% to 176%. The percentage of temporary imprint in total imprint depth (x/H) varied from 12 to 33% (linden 12–18%—the lowest self-re-deformation ability; beech 25–33%—the highest self-re-deformation ability). The results of this study underline that the higher the density of the wood, the higher the Brinell hardness, and, simultaneously, the greater the measurement force used, the higher the Brinell hardness measured. The ability of self-re-deformation in wood’s R and T cross-sections depends on the wood density and the measuring force used. In contrast, this ability only depends on the wood density in the L cross-section. Those observations imply that the compaction of the cell structure during side compression is mainly non-destructive, while the longitudinal deformation of the cell structure (the buckling of cell walls and fracture of ends of the cells) is to a great degree destructive and irreversible. These results can be used in the construction and furniture sectors, especially when designing products and planning the woodworking of highly loaded wood floors and furniture elements.
At present, forest enterprises face many challenges in adopting innovative bio-based approaches considering global changes. Due to the specifics of forestry, the choice of financing sources is a complex issue. The aim of this study is to estimate the capital structure determinants of forest enterprises in the Czech Republic, Slovakia, and Bulgaria in the context of the relationship between leverage and the factors of its appearance. The evaluation of capital structure determinants was carried out using selected indicators for 18 forest enterprises, with 6 enterprises per country. Data were processed for the period of 2015–2019. The study methodology was based on a Panel Data Analysis with Fixed Effects and Random Effect models and Ordinary Least Squares estimation. The following specific variables were included: liquidity, leverage, return on assets, size of the enterprises, and gross domestic product. The results revealed that the forest enterprises in these three countries can be differentiated by size and form individual functional relationships with the positive influence of enterprise size on liability share. The next significant determinant was found to be liquidity, which has a negative relationship with enterprise leverage. These results will be useful for managers of forest enterprises in decision-making processes to determine the amount of debt and planning investment programme strategies.
Aquaponics is a specific ecosystem that combines aquaculture, hydroponics and beneficial bacteria in a symbiotic relationship. This integrated approach is emerging as a sustainable method of organic food production. This review analyzes the biological and technological parameters of aquaponic systems based on a survey of over 200 scientific papers from 1974 to 2021. The biological parameters include the characteristics of the species in the aquaponic system, their relationship with nutrition and environmental conditions, the content of nutrients and their impact on productivity. The technological parameters focus on the structural and functional components of the aquaponic system, environmental management techniques and economic feasibility. The advances in aquaponics technology contribute to more sustainable food systems. This calls for further research on the biological and technological characteristics of aquaponic systems, as well as on the environmental, operational and socio-economic aspects and their interrelationship, of interest to both researchers and stakeholders.
Proposing a microscopic model we have investigated the multiferroic properties of Sm2BaCuO5. The heat capacity shows two peaks at the antiferromagnetic transitions temperatures TN1 ∼ 5 K and TN2 ∼ 23 K. For the appearing of the extraordinary polarization ΔP in Sm2BaCuO5 we have considered the single-ion magnetosriction mechanism. ΔP is zero without magnetic field. An external magnetic field h induces an electric polarization ΔP below TN2 which varies linearly with h showing a linear magnetoelectric effect. Below TN1 ΔP decreases due to ordering of the Sm-sublattice. There are some discrepancies in the experimental data for ΔP(T,h) which we will try to clarify. In addition, the temperature and magnetic field dependence of the dielectric constant is discussed. The observed maximum value of the peak at TN2 shifts to smaller temperature values and increases with increasing external magnetic field.
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357 members
Stela Tasheva
  • Department Forest Management
Teodora Popova
  • Faculty of Veterinary Medicine
Danail Doychev
  • Department of Plant Pathology and Chemistry
Kalin Jordanov Hristov
  • Faculty of Veterinary Medicine
Alexander Nikolov Tashev
  • Department of Dendrology
Kliment Ohridski Blvd., 1797, Sofia, Sofia-Capital, Bulgaria
Head of institution
Ivan Iliev