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In this research, an attempt was made to produce safe food from lead-contaminated soil. It was assumed that an increased amount of calcium (Ca) in plants would prevent them from lead (Pb) uptake. A new-generation agricultural product − an activator of Ca transport in plants “InCa” (from Plant Impact) − was used. The study was conducted on several crop species, Cucumis sativus L., Linum usitatissimum L., Medicago sativa L. and Solanum lycopersicum L., cultivated in mineral medium. The leaves were sprayed with InCa activator while the roots received Pb from the substrate in the form of Pb(NO3)2 dissolved in the medium. It was shown that spraying the leaves with InCa reduced Pb concentration in the roots of S. lycopersicum to 73%, in C. sativus to 60%, and in L. usitatissimum to 57%. Finally, it was found that foliar application of InCa reduced the concentration of Pb in plant roots by 53%, and in plant shoots by 57% (on average by about 55%). These observations were confirmed using histochemical and electron microscopy techniques. It was shown that one of the InCa activator components – Ca(NO₃)₂ – is responsible for such effects. This result was verified by using another experimental method – the Allium epidermis test. Visualization of Pb in epidermal cells of Allium cepa. L. using the Leadmium™Green fluorescent probe (confocal microscopy) showed a reduction in the amount of Pb that entered the epidermal cells after the application of the tested solutions. For the first time, it was shown that it is possible to reduce Pb uptake by plants by up to 55%. In the future, this offers the possibility of developing a foliar calcium preparation aimed at lowering the concentration of Pb in plants and thereby reducing the amount of Pb in the food chain.

Seedling emergence from soil seed bank was studied during 3 growing seasons 1997-1999 in: 1) 60 plots in 3 parts of the Potentillo albae-Quercetum patch: A - with Carpinus betulus (hornbeam) present only in the herb layer (canopy cover ca. 50-60%), B - after tree felling, at present with hornbeam dominating the shrub layer (cover > 90%), C - invaded by hornbeam 30-40 years ago (cover ca. 90%), and in 2) 60 soil samples from objects A, B, C kept in an unheated glasshouse. The results suggest that the seed bank realised in natural conditions is poorer in species with high light requirements (the Ellenberg indicator values for light (L ≥ 6) and their seedlings in comparison with the potential seed bank estimated in glasshouse conditions (field: A- 24; B - 17; C- 7, glasshouse : 44; 38; 32 species / 2 m2, field: 321; 108; 14, glasshouse: 785; 1205; 177 seedlings / m2, respectively). Contrarily, more species and seedlings with moderate light demand (L = 3-5) appeared in the field plots (field: A- 26; B- 25, glasshouse: 20; 14 species / 2 m2, field: 1014; 310, glasshouse: 328; 71 seedlings / m2). The shading by hornbeam negatively influences the size of the seed bank (field: A - 1743; B - 1226; C - 680, glasshouse: 1547; 3274; 459 seedlings / m2) and its species richness (field: A- 55; B - 48; C - 19, glasshouse: 76; 59; 56 taxa / 2 m2). Nomenclature: syntaxa - Matuszkiewicz (1981), taxa - Mirek et al. (1995).

The research was conducted on four patches of thermophilous oak wood in Białowieża Primeval Forest: A – with a woodstand: oak + approx. 30-year-old hornbeam + hornbeam brushwood; B – with a hornbeam stand formed by natural seed fall after logging (ca. 1920) oaks; C – after logging oaks and replanted (ca. 1965) with pine and oak; D – with a natural low-density oak stand. Species composition and seed bank density were estimated using the seedling emergence method. Seedling emergence was observed over two vegetation seasons. Research demonstrated that: 1) the species abundance of the seed banks depends on canopy cover (A, B approx. 50 species; C, D approx. 70 species); 2) the floristical similarity (Sørensen's index) of the seed bank and ground vegetation is higher in the undisturbed patch D (0.50) than in disturbed patches (0.30-0.35); 3) species diversity in plots A, B, C, D (H'=12.5; 13.4; 15.5; 16.9) and seed bank density per m2 (432.5; 958.0; 1486.5; 2268.0) are negatively correlated with the degree of patch shading; 4) the average weight of diaspores in the seed banks of shady plots is lower (A, B approx. 0.003 g) than that of sunny plots (C, D approx. 0.08 g); 5) the share of long-lived diaspores increases in patches after logging.

Atriplex tatarica is an invasive annual plant from Central Asia. It is an early successional species of disturbed habitats, tolerant of a high content of NaCl. It grows also by the roadsides, on lawns by the streets and other places in cities sprayed with salt during snowfalls. The paper presents results of the analysis of abundance and patterns of occurrence of this invasive subhalophytic plant by the roadsides in the Warsaw city. We found that frequency and distribution of Atriplex tatarica increased significantly over the last few decades. The species grows chiefly along main streets which are de-iced. It forms monodominant patches of different length at the zone closest to the street verge. The NaCl concentration there is significantly higher than in the zones more distant from the street verge, although this parameter is very variable. The cover of other species increases with an increasing distance from the roadside verge.