To better manage invasive populations, it is vital to understand the environmental drivers underlying spatial variation in demographic performance of invasive individuals and populations. The invasive common ragweed, Ambrosia artemisiifolia, has severe adverse effects on agriculture and human health, due to its vast production of seeds and allergenic pollen. Here, we identify the scale and nature of environmental factors driving individual performance of A. artemisiifolia, and assess their relative importance. We studied 39 populations across the European continent, covering different climatic and habitat conditions. We found that plant size is the most important determinant in variation of per-capita seed and pollen production. Using plant volume as a measure of individual performance, we found that the local environment (i.e. the site) is far more influential for plant volume (explaining 25% of all spatial Published in "Biological Invasions doi: 10.1007/s10530-017-1640-9, 2018" which should be cited to refer to this work. variation) than geographic position (regional level; 8%) or the neighbouring vegetation (at the plot level; 4%). An overall model including environmental factors at all scales performed better (27%), including the weather (bigger plants in warm and wet conditions), soil type (smaller plants on soils with more sand), and highlighting the negative effects of altitude, neighbouring vegetation and bare soil. Pollen and seed densities varied more than 200-fold between sites, with highest estimates in Croatia, Romania and Hungary. Pollen densities were highest on arable fields, while highest seed densities were found along infrastructure, both significantly higher than on ruderal sites. We discuss implications of these findings for the spatial scale of management interventions against A. artemisiifolia.

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...

Echinochloa crus-galli (L.) P. Beauv. is the most common monocotyledonous weed in maize crops in Croatia. Crop–weed interference is influenced by weed emergence patterns, and knowledge of the timing of weed emergence is crucial for the development of an efficient integrated weed-management program. Therefore, two-year field experiments were conducted in a maize crop sown in early May in continental Croatia to determine the emergence pattern of E. crus-galli from natural seedbank. In laboratory studies, the estimated base temperature and base water potential for the Croatian ecotype of E. crus-galli were 10.8 °C and −0.97 MPa, respectively. Then, the estimated germination parameters were compared with the values embedded in the AlertInf model from Italy (Veneto) to calibrate this hydrothermal model. The estimated hydrothermal units were around 28 for the onset (10%) and 93 for the middle (50%) emergence of E. crus-galli. Our findings showed that the AlertInf model satisfactorily simulated the emergence of E. crus-galli in maize crop in Croatia (EF = 0.97 in 2019 and 0.98 in 2020), indicating its potential use in other geographical areas

Effective weed management depends on correct control timing, which depends on seedling emergence dynamics. Since soil temperature and soil moisture are the two main factors that determine weed germination, the hydrothermal time model can be used to predict their emergence. The aim of this study was to estimate the base temperature (Tb) and base water potential (Ψb) for the germination of Chenopodium album, Amaranthus retroflexus, Setaria pumila, and Panicum capillare collected from fields in continental Croatia and then to compare these values with those of Italian populations embedded in the AlertInf model. Germination tests were performed at seven constant temperatures (ranging from 4 to 27 °C) and eight water potentials (0.00–1.00 MPa). The estimated Tb and Ψb were 3.4 °C and −1.38 MPa for C. album, 13.9 °C and −0.36 MPa for A. retroflexus, 6.6 °C and −0.71 MPa for S. pumila, and 11.0 °C and −0.87 MPa for P. capillare, respectively. According to the criterion of overlap of the 95% confidence intervals, only the Tb of C. album and the Ψb of A. retroflexus of the Croatian and Italian populations were similar. Further field experiments should be conducted to monitor the weed emergence patterns of C. album and calibrate the AlerInf equation parameters.

Summary Abutilon theophrasti is a weed that is spreading worldwide and that has had to adapt to different combinations of environmental conditions. Wide interpopulation variability has been reported regarding dormancy and germination. This variability, controlled by the interaction of genetic diversity and maternal effect, could hinder the adoption of Integrated Weed Management (IWM) tools. A collaborative project was conducted to compare emergence dynamics of 12 European and North American populations under diverse environmental conditions. The main aim was to assess interpopulation variability and explain this according to environmental conditions in the seed collection sites. Seeds were sown at six experimental sites, and seedling emergence was monitored. The AlertInf model was tested to evaluate its ability to predict emergence dynamics of the different populations. A wide interpopulation variability was observed for emergence percentage and dynamics with consistent trends across sites and related to different seed dormancy levels. Populations from Catalonia, Iowa and Minnesota reached higher emergence percentage with earlier and concentrated emergence flushes probably due to low dormancy level, while populations from Croatia, Serbia and Hungary, given their low average emergence percentage, presented high dormancy levels. Good predictive accuracy of AlertInf model was obtained at the different sites, confirming the possibility of adopting it across a wide range of environmental conditions. Achieving a better knowledge of interpopulation variability can allow specific control strategies to be designed, facilitating the replacement of solely herbicide‐based management with true IWM.