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This review paper is the first that summarizes many aspects of the ecological role of trees in urban landscapes while considering their growth conditions. Research Highlights are: (i) Plant growth conditions in cities are worsening due to high urbanization rates and new stress factors; (ii) Urban trees are capable of alleviating the stress factors they are exposed to; (iii) The size and vitality of trees is related to the ecological services they can provide. Our review shows, in a clear way, that the phenomenon of human-related environmental degradation, which generates urban tree stress, can be effectively alleviated by the presence of trees. The first section reviews concerns related to urban environment degradation and its influence on trees. Intense urbanization affects the environment of plants, raising the mortality rate of urban trees. The second part deals with the dieback of city trees, its causes and scale. The average life expectancy of urban trees is relatively low and depends on factors such as the specific location, proper care and community involvement, among others. The third part concerns the ecological and economic advantages of trees in the city structure. Trees affect citizen safety and health, but also improve the soil and air environment. Finally, we present the drawbacks of tree planting and discuss if they are caused by the tree itself or rather by improper tree management. We collect the latest reports on the complicated state of urban trees, presenting new insights on the complex issue of trees situated in cities, struggling with stress factors. These stressors have evolved over the decades and emphasize the importance of tree presence in the city structure.

Plant functioning is affected by drought, extreme temperatures, heavy metal pollution and other unfavorable environmental conditions. High intensity of stress factors can be lethal to sensitive organisms or significantly decrease their condition. Intensification of stress factors is observed especially in urban and industrial areas. During the vegetative season plants purify the air and soil, decrease air temperature, increase humidity and have others psychosociological advantages. It is especially important to monitor growth of plants in areas with high anthropopression. In presented study condition of silver birch (Betula pendula Roth) growing in different stressful environments was investigated. During the research soil parameters such as pH, EC and heavy metals content were observed. Chlorophyll a fluorescence, photosynthetic pigment content, phenolic compounds concentration, ability to scavenging DPPH free radical, activity of anti-oxidative enzymes (superoxide dismutase-SOD, peroxidase-POD, catalase-CAT) were examined in the leaves to study plant response to stress factors. Investigated trees showed two types of antioxidative defense systems: with high activity of low molecular weight antioxidants (phenolics) or with high enzymatic antioxidant activity. The most stressed trees showed highest concentration of low molecular weight antioxidants (phenolics).

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Abstract:For several decades an increase of platinum in the environment was recorded. This is connected with the release of platinum from automobile catalytic converters and pharmaceutical industries. In the conducted experiments the effect of various forms and concentrations of platinum on the germination and roots growth of different plants (oat, garden cress and tomato) was investigated. Two separate experiments were performed with lower (experiment 1 st : 1, 5 and 10 mg/L) and higher (experiment 2 nd : 10, 20 and 40 mg/L) [Pt(NH 3 ) 4 ](NO 3 ) 2 or PtCl 4 dosages.There was no significant effect of dose and form of platinum on the germination of seeds (experiment 1 st and 2 nd ). The effect of platinum containing substances dose on root growth of young seedlings was observed during experiment, dependent on the species of tested plants.The root length of oat plants was similar in all treatments in experiment 1 st . The shortest tomato roots were observed in the case of a 10 mg/L of PtCl 4 , it was statistically shorter than the control plants (treated with water) as well. The roots of the tomato treated with [Pt(NH 3 ) 4 ](NO 3 ) 2 were the same length as observed for the control sample. The garden cress root growth was not affected by [Pt(NH 3 ) 4 ](NO 3 ) 2 , but a solution containing Pt 4+ stimulated the root growth.The roots of tomato and oat treated with [Pt(NH 3 ) 4 ](NO 3 ) 2 had similar length as the control plants in contrast to the far shorter roots treated with PtCl 4 (experiment 2 nd ). Moreover, the treatment with [Pt(NH 3 ) 4 ](NO 3 ) 2 stimulated the growth of garden cress roots compared to the control, while only the lowest dose of PtCl 4 stimulated the root growth.