Trapa natans is one of the very few plants that generate so many contrasting views: it is highly endangered in Europe, invasive in North America and Australia, yet highly valued in India and China due to its nutritional and medical properties. Its endangered status in most of the Europe has prompted significant conservation efforts aimed at retention and expansion of its population. T. natans is currently on the red list of many European countries and is included under “Appendix I” of the “Convention on the conservation of European wildlife and natural habitats” (Bern Convention) and IPA list (IPA criterion A, threatened species). The unusual circumstances, i.e. endangered status of T. natans in the region on one hand and its expansion in Serbia on the other, are the reason behind this research that aims to present the distribution, floristic composition and ecological conditions of ass. Trapetum natantis stands in hydromeliorative facilities (Serbia), comprised of 28 hydrophytes. In the analyzed stands, based on the long-term phytocenological studies, we have singled out four floristic and ecological groups: the stands in which T. natans predominates, the stands with Ceratophyllum demersum, the stands with lemnids plants (Lemna minor, L. gibba, Spirodela polyrrhiza) and Salvinia natans and the stands with Hydrocharis morsus-ranae. In the researched localities, the differentiation of ass. Trapetum natantis stands is predetermined by the phosphorus and nitrate content, as well as pH and BOD₅ levels.

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Sixty-five plant species have been found in Lake Provala (the Vojvodina Province, Serbia) and its riparian zone. Among them, three hydrophytes were dominant: Nymphoides peltata, Myriophyllum spicatum and Ceratophyllum demersum. As interactions between different ecological factors, especially light, temperature and nutrient level, are of prime importance for productivity of macrophytes, we analyzed the main physical and chemical indicators of water quality in the studied location. In the vegetation period of the year 2000, the dominant hydrophytes were analyzed for biomass production dynamics in the studied aquatic ecosystem, including fresh weight (FW), dry weight (DW) and ash free dry weight (AFDW). The studied plant species achieved maximum biomass production in June, with statistical differences among the species at the significance level of α = 0.05.

Abstract:The objective of this investigation was to analyze the primary production of the dominant hydrophytes by monitoring levels of organic matter and organic carbon and estimating photosynthetic potential via the total chlorophyll content. The survey was conducted in Lake Provala (Serbia) throughout the peak vegetation period of the year 2000. . Chlorophyll A (Chl a) and chlorophyll A+B (Chl a+b) pigments ranged from 1.54 mg g (Chl a+b) in C. demersum. At full leaf out, the latter aquatic plants exceeded 50% cover of the open water surface. All species achieved maximum growth in June, but significant differences in growth dynamics were observed. At the end of the vegetation period, these plants sink to the bottom and decompose

The study?s aim is the comparative chorologic and ecological analysis of the vascular flora of the two gorges of the Pcinja River in Serbia and Macedonia which are 27 km apart. In the two gorges 1564 taxa have been recorded, 1057 being in the upper gorge in Serbia and 1174 in the lower gorge in Macedonia. Common to both gorges are 666 taxa. Chorological spectra show that in both gorges the most abundant are Mediterranean-submediterranean plants, 32.85% being in the upper and 43.97% in the lower gorge. Differences in the studied vegetation result from a diverse participation of other floristic elements such as Central European ones that are more abundant in the upper gorge (17.05%) than in the lower gorge (10.86 %). The life-form spectrum reveals that the flora in both gorges is hemicryptophyte-therophyte in character. Both gorges belong to an enclave of a Mediterranean-submediterranean region, i.e. to its submediterranean Macedonian- Thracian province.

ScienceDirect Ground cover management and farmyard manure effects on soil nitrogen dynamics, productivity and economics of organically grown lettuce (Lactuca sativa L. subsp. secalina

Nymphaeion alliance vegetation is dominant floating-leaved vegetation in the Danube-Tisza-Danube hydrosystem in northwestern Serbia and comprises Nymphaeetum albae, Nymphaeetum albo-luteae, Nymphoidetum peltatae and Trapetum natantis associations. Comparative analysis of physical-chemical water parameters on localities where these -in most parts of Europe endangered and vulnerable stands -develop showed that most phytocenoses are associated with specific habitat conditions. Of the analyzed water properties, the factors that cause Nymphaeion alliance phytocenoses differentiation are primarily pH, alkalinity and COD-MnO 4 . Formation of the Nymphaeetum albae stands is significantly associated with the highest values of pH, COD-MnO 4 and alkalinity, and the lowest nitrate, nitrite, dissolved and the total phosphorus content values, in comparison to the other studied associations. Nymphoidetum peltatae stands develop in waters characterized by the lowest pH and COD-MnO 4 , low alkalinity, and the highest nitrate and nitrite values in relation to the other analyzed phytocenoses. Trapetum natantis stands, on the other hand, prefer the warmer sections of the canal network, neutral pH, and the highest values of BOD 5 , dissolved and total phosphorus. Habitat conditions in which Nymphaeetum albo-luteae stands develop are of the widest range in comparison to other investigated phytocenoses.

Summary:This study was performed to compare the weed flora in dill crops maintained conventionally and according to the principles of organic production. Out of 17 weed species noted for the two growing systems, even four (Amaranthus retroflexus L., Datura stramonium L., Sorghum halepense (L.) Pers., and Veronica persica Poir.) are invasive in Vojvodina region (Serbia). Weed infestation (number of individuals per m 2 ) was significantly higher on the conventional plots (p = 0.0000 ** ). The dominating species in conventional growing system were Convolvulus arvensis, Veronica persica and Chenopodium album (8.00, 6.67 and 5.33 individuals per m 2 , respectively), while Amaranthus retroflexus dominated on organic plots (8.00 individuals per m 2 ). Regarding life forms of the recorded weed flora, therophytes dominate both in conventional (92.31%) and organic (66.67%) systems. The observed differences in weed flora are due to the specificities of dill conventional and organic production.