Information on ecotoxicity of organic contaminants, such as polycyclic aromatic hydrocarbons (PAHs), in terrestrial environment is needed for establishing soil quality criteria and for risk assessment purposes. An ecotoxic effect of a model PAH compound (phenanthrene) toward soils microorganisms (nitrifying bacteria) was evaluated in 50 different soils. The soil samples were collected from agricultural land in four regions of Poland with varying levels of industrialization (Slaskie, Dolnoslaskie, Podlaskie, and Lubelskie voievodeships). Soils were characterized for basic physicochemical properties (texture, organic matter content, pH(KCl), total nitrogen content, total sorption capacity) and the content of contaminants including PAHs (73-800 microg kg(-1)), Pb (6-720 mg kg(-1)), and Zn (9-667 mg kg(-1)). Ecotoxicity of phenanthrene (applied at 10, 100, 500, and 1000 mg kg(-1)) to soils microorganisms was evaluated in laboratory studies in control conditions (incubation of soils for 7 d at 20 +/- 2 degrees C). Nitrification potential was used as the ecotoxicity measurements end point. The EC50 values (146-1670 mg kg(-1)) calculated from the square root-X linear regression model differed significantly in various soils, although it was difficult to establish a causative relationship between soil physicochemical characteristic and phenanthrene toxicity. A significant factor in the assessment of soils vulnerability to the effect of phenanthrene was level of soil contamination, particularly with PAHs. Soils with previous contamination were more susceptible (mean EC50, 325 mg kg(-1)) than soils from uncontaminated, rural areas (mean EC50, 603 mg kg(-1)).

Agricultural management can affect soil chemistry, nutrient cycling and microbial properties, but the relationship among them is not well explored. Catch crops play an important role in decreasing nitrogen (N) leaching in the autumn, and thereby reduce undesirable environmental effects, improve soil physical and microbiological properties. We investigated the effect of catch crops and straw management on soil mineral nitrogen (N min ) and microbial activity on a clay loam Gleyic Cambisol (CMg). A two-factor experiment was set up: 1) catch crops (narrow-leafed lupin, mixture of narrow-leafed lupin and oats, white mustard and without catch crops), and 2) straw management methods (with and without). The total amount of bacteria and fungi, dehydrogenase and urease activity, and potential nitrification rate were assayed during two successive spring barley growing seasons. Also we determined N in the soil and soil leachate. Our experimental findings indicated that the N min dynamics in the soil and nitrate nitrogen (N-NO 3 ) leaching depended on the catch crops, the amount of decomposers and the weather conditions. Cultivation of post-harvest catch crops in a clay loam Cambisol reduced N min content by 50-62% at the 0-40 cm soil layer, stubble breaking in the autumn by 23-41%, compared with the soil where the stubble had not been broken and no catch crops had been grown. Also, cultivation of catch crops reduced nitrate (N-NO 3 ) concentration in the soil leachate by 32-62%. The biological variables differed among all treatments, especially among years. Higher counts of heterotrophic bacteria and fungi and greater enzymatic activity were recorded in the plots with catch crops. Higher nitrification activity was established in the plots without catch crops. The amount of cellulose degrading bacteria did not differ significantly between the treatments. Further research is needed to get a better insight into the processes of mineralization and immobilization of catch crops' residues and soil N min and N-NO 3 leaching in agricultural ecosystems.

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Leaf litterfall decomposition of pedunculate (Quercus robur L.) and sessile (Q. petraea [Matt.] Liebl.) oaks and their hybrids and its impact on soil microbiota Received: 18 August 2016; Accepted: 31 March 2017 Abstract: Trakas Forest is the only natural habitat of sessile oak in Lithuania. Sessile oak stand here is growing about 60-70 km from the nearest natural sessile oak stands in Poland. The purpose of this study was to determine whether autumn leaf litterfall of pedunculate and sessile oaks and their hybrids have different biochemical composition and decomposition rate and, consequently, different impacts on microbial condition of rhizosphere. For this purpose in autumn leaf litterfall C, N, P, K, Ca, Mg, lignin, ash, fat, crude fibre and water-soluble carbohydrates contents and stocks, lignin/N, lignin/P, C/N, C/P, N/P ratios, the decomposition rate and CO 2 emissions were determined. In rhizosphere of studied oak species N, C concentration, pHH 2 O, C/N ratio, and dehydrogenase, urease, phosphatase, bacteria and micromycetes amount were estimated as well. The litterfall of pedunculate oak was distinguished by a higher content of lignin, higher lignin/N ratio, lower decay rate and lower carbon release, which determines decreased activity of micromycetes in the rhizosphere. Metabolic activity of microorganisms differed insignificantly among tree species rhizospheres. However, the potential for the use of carbon compound substrates and biodiversity index have a tendency to be higher in the soil under sessile oak. Lower decomposition rate of leaf litterfall and organic compounds in the rhizosphere under pedunculate oak allowed to suppose that the conditions for natural regeneration were more suitable in stands where sessile and hybrid oaks dominate.

Little is known about the response of spring barley (Hordeum vulgare L.) physiological parameters to stand density, on which barley productivity depends. The aim was to establish the contrasts of physiological parameters between the different varieties and different stand densities under field conditions and the interaction between physiological parameters and meteorological factors of Lithuania (East Europe). The test involved three barley varieties and three stand densities. The measurements were made three times during the growing season. Varietal and stand density effect on photosynthetic rate, transpiration rate, and instantaneous water use efficiency was more strongly expressed in wet conditions compared with dry conditions. The spring barley varieties differed in the tolerance of meteorological factors throughout the growing season. The photosynthetic process was more intensive for the variety 'Barke' in dry and for 'Gustav' in wet weather conditions conditions. A medium density of 400 plants m -2 was the optimum. With the change in stand density, physiological parameters tended to decrease in most of the tested cases. The interaction of meteorological factors influenced the mean of photosynthetic rate across stand densities by 52.1, 67.1 and 73.6 % and the mean of transpiration rate by 63.3, 61.1 and 72.0 % for 'Aura DS', 'Barke' and 'Gustav', respectively.