The aim of this research was to examine the influence of acorn size on morphological characteristics of one-year-old Northern red oak (Quercus rubra L.) seedlings. The quality of seedlings correlates with the quality of the seed they are derived from. In species with large seeds, as in the case of Northern red oak, the seedling growth in the first growing season is closely related to seed size or the amount of reserve nutrients that are stored in the seed. The height and root collar diameter of one-year-old Northern red oak seedlings increases with increase in acorn size. The results obtained in this research can be used as a guideline for acorn grading, because they show that improved Northern red oak seedlings quality can be achieved using seeds of appropriate size.

The paper presents the results of the analysis of genetic variability of eight populations of silver fir (Abies alba Mill.) in Serbia obtained using SSR markers. The genomic DNA was isolated from tissue of needles of all eight populations. Due to the costly and lengthy process a small number of the SSR markers for Abies alba have been developed, so in this study were used the microsatellite markers of related species. The obtained results indicate a low level of the genetic variability between natural populations of silver fir. The total number of alleles detected with nine SSR markers in eight studied populations of silver fir is 28. The range of alleles varies from two for NFF15 to six for SF78 with an average of 3.1 alleles per locus. The mean value of genetic similarity between populations is 0.92. The smallest genetic similarity between pairs of populations is 0.82 (Dubocica Bare and Stara Planina; Dubocica Bare and Tara) and the greatest genetic similarity is 1 (Zlatar and Stara Planina, Zlatar and Tara, Stara Planina and Tara). A basic insight into the level of genetic diversity of natural populations of silver fir in Serbia, which are located in a relatively small area, has been given using a set of SSR markers. The obtained results can be used in the future strategy for the management and regeneration of silver fir forests.

Water regulation, integral water management and water conservation are one of the main tasks, set by an ecologically conscious society. A series of complex treatments are set in order to achieve the main goal in wastewater treatment, i.e. eliminating or reducing pollutants to a level that will not cause adverse effects to humans and the environment. The paper presents the construction of an efficient, environmentally friendly and economically justified biological system for the treatment of polluted urban waters. Research has shown that the proposed system with floating islands and algae was effective in removing various categories of pollutants from polluted river (organic and inorganic matter, heavy metals and pathogenic microorganisms), which indicated that the selected type of construction was appropriate. It was concluded that minor modifications in terms of cell coverage by floating islands could provide even greater removal of certain pollutants such as nitrogen, phosphorus and heavy metals.

Wild cherry ( Prunus avium L.) is the most important European tree species in the family Rosaceae (Russell 2003). It is very valuable forest species that grows in mixed forests in Southern, Central and Western Europe. In the growing...