At the global level, the invasion of alien organisms is considered the second largest threat to biodiversity. The assumption is that the high allelopathic potential is one of the features that helps invasive plant species to spread to new areas. Allelopathic potential of 8 invasive plant species (donor species) and their impact on test-species was determined in the study. Donor species were velvetleaf (Abutilon theophrasti Med.), ragweed (Ambrosia elatior L.), jimsonweed (Datura stramonium L.), common cocklebur (Xanthium strumarium L.), tree of heaven (Ailanthus altissima (Mill.) Swingle), indigo bush (Amorpha fruticosa L.), Japanese knotweed (Reynoutria japonica Houtt.) and giant goldenrod (Solidago gigantea Aiton). Three cultivated plant species from 3 different plant families were used as test-species. Test-species were: oat (Avena sativa L.), oilseed rape (Brassica napus subsp. oleifera) and sunflower (Helianthus annuus L.). Water extracts made of whole plants of donor species were applied to the seeds of the test-species. High allelopathic potential was proven for all species included in experiment. Allelopathic effects were exclusively negative. Impact on germination for all species was much lower in relation to the impact on the radicle and shoot length of the test-species. Perennial donor species had a stronger allelopathic potential than annual donor species. Tree of heaven was the species with the strongest allelopathic potential. Its extracts inhibited germination, radicle and shoot length of oilseed rape by 19%, 94.88% and 98.91% respectively. Keywords SažetakNa globalnoj razini, invazije alohtonih organizama predstavljaju drugu najveću prijetnju bioraznolikosti. Pretpostavka je da je visok alelopatski potencijal jedna od značajki koja pomaže invazivnim biljnim vrstama u širenju na nova područja. U radu je određen alelopatski potencijal 8 invazivnih biljnih vrsta (donor vrsta) i njihov učinak na test-vrste. Donor vrste su bile europski mračnjak (Abutilon theophrasti Med.), pelinolisni limundžik (Ambrosia elatior L.), bijeli kužnjak (Datura stramonium L.), dikica (Xanthium strumarium L.), pajasen (Ailanthus altissima (Mill.) Swingle), amorfa (Amorpha fruticosa L.), japanski dvornik (Reynoutria japonica Houtt.), velika zlatnica (Solidago gigantea Aiton). Kao test-biljke korištene su 3 kultivirane biljne vrste iz 3 različite biljne porodice: zob (Avena sativa L.), uljana repica (Brassica napus L.) i suncokret (Helianthus annuus L.). Vodeni ekstrakti napravljeni od cijelih biljaka donor vrsta aplicirani su na sjeme test-vrsta. Dokazan je visok alelopatski potencijal za sve vrste uključene u istraživanje. Alelopatski učinci bili su isključivo negativni. Učinak na klijavost svih vrsta mnogo je manji u odnosu na učinak na duljinu korjenčića i klica test-vrsta. Kod višegodišnjih donor vrsta zabilježen je jači alelopatski potencijal nego kod jednogodišnjih donor vrsta. Pajasen (Ailanthus altissima (Mill.) je vrsta s najjačim alelopatskim potencijalom. Njegovi ekstrakti inhibirali su klijanje, duljinu...

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Croatia is a small but heterogeneous country with different pedo-climatic conditions in its parts. In the continental region, mountain region excluded, the climate is moderate continental and in the coastal region Mediterranean and sub-Mediterranean. The aim of this study was to explore the presence, prevalence and level of aggressiveness of some invasive alien plants between continental and coastal part of Croatia. Amorpha fruticosa L., Reynoutria japonica Houtt. and Solidago gigantea Ait. are widespread and very aggressive in the continental and rarely present in coastal part of Croatia. Ailanthus altissima (Mill.) Swingle is present in each Croatian county but it shows greater aggressiveness in the coastal region, including islands and some protected areas.