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Background and purpose: This paper analyses the lead tolerance and accumulation in white poplar genotypes in vitro, in order to optimize genotype evaluation and other procedures in their implementation in phytoremediation projects and landscaping in areas endangered by lead accumulation. Material and Methods: The lead tolerance and accumulation of five white poplar genotypes after 35 days in vitro cultivation on media supplemented with lead was examined. The following Pb(NO 3) 2 concentrations were used: 0, 10-6 , 10-5 , 10-4 and 10-3 M. Tolerance analysis (described by tolerance indices) was based on morphological parameters, biomass accumulation and the content of photosynthetic pigments, while lead accumulation was described by shoot lead accumulation and shoot lead content. Results and Conclusions: The chosen lead concentrations appeared not to be lethal. Moreover, the obtained results showed that the tested lead concentrations had a positive effect on: number of formed roots, shoot moisture content and shoot height. The best differentiation among the examined genotypes was gained by the tolerance index based on the shoot height on 10-4 M Pb(NO 3) 2. The shoot lead accumulation and shoot lead content significantly increased on 10-4 and 10-3 M Pb(NO 3) 2 media. Thus, the concentration of 10-4 M Pb(NO 3) 2 is recommended for further research. Two examined genotypes of horticultural value (LCM and LBM) achieved a significantly higher lead shoot content compared to the wide spread genotype "Villafranca" (almost 200% and 125% higher, respectively).

The antiozonant ethylene diurea is proven to prevent growth reductions in forest trees induced by ozone. The community of mycorrhizal fungi could be useful indicator of environmental stress. In this study, response of mycorrhizal fungi and fine roots to a 4-year exposure to ambient ozone and treatment with antiozonant was investigated in ozone-sensitive poplar clone under field conditions. The community of ectomycorrhizal fungi and root length colonization with ectomycorrhizal, arbuscular mycorrhizal fungi, and root endophytic fungi was analyzed in antiozonant-treated poplar plants and in poplar plants irrigated with water. In general, plants protected by antiozonant showed higher total number of fine roots, number of ectomycorrhizal types, Shannon-Weaver diversity index, and Species richness index compared to the plants treated with water. The ectomycorrhizal community shifted from contact exploration type in the trees irrigated with water to short-distance exploration type in ethylene diureatreated trees. Ozone protectant may beneficially affect the belowground community of mycorrhizal fungi colonizing roots of ozone-sensitive poplar clone. Keywords Ground-level ozone Á Ectomycorrhizal fungi Á Antiozonant ethylene diurea Á Fine roots Á Root length colonization Á Populus maximoviczii 9 berolinensis This article originates from the IUFRO Conference ''Biological Reactions of Forests to Climate Change and Air Pollution,'' held in Kaunas/Lithuania during May 18-27, 2012, as organized by IUFRO Research Group 7.01.00 in cooperation with COST Action FP 0903 ''MAFor,'' North American Air Pollution workshop ENVeurope and ICP monitoring task force (local organizer: Algirdas Augustaitis).

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The effect of low initial medium pH on shoot and root development of five white poplar (Populus alba L.) genotypes was tested. The shoot height, fresh mass of shoots per jar, dry mass of shoots per jar, number of roots, as well as the length of the longest root were measured and final pH of the media determined, after 35 days of culture in vitro. Three initial pH values of the medium were tested: 3.0, 4.0 and 5.5 as control. Agar solidification at pH 3.0 was not achieved after sterilization in autoclave, but it was successful after sterilizing in a microwave oven. The obtained results indicate that the tested genotypes are able to significantly influence the changes of media pH during culture. The effect of differences among the examined media was significant for biomass accumulation and final media pH. Generally, significantly higher values of fresh and dry shoot mass, shoot height and the longest root length were recorded on a medium with initial pH 3.0 then on a standard medium with pH 5.5.The implications of the obtained results for the improvement of in vitro propagation of white poplars are discussed. [Projekat Ministarstva nauke Republike Srbije, br. 43007: Studying climate change and its influence on the environment: impacts, adaptation and mitigation