Ambrosia artemisiifolia is an invasive weed in Europe with highly allergenic pollen. Populations are currently well established and cause significant health problems in the French Rhône valley, Austria, Hungary and Croatia but transient or casual introduced populations are also found in more Northern and Eastern European countries. A process-based model of weed growth, competition and population dynamics was used to predict the future potential for range expansion of A.artemisiifolia under climate change scenarios. The model predicted a northward shift in the available climatic niche for populations to establish and persist, creating a risk of increased health problems in countries including the UK and Denmark. This was accompanied by an increase in relative pollen production at the northern edge of its range. The southern European limit for A.artemisiifolia was not expected to change; populations continued to be limited by drought stress in Spain and Southern Italy. The process-based approach to modelling the impact of climate change on plant populations has the advantage over correlative species distribution models of being able to capture interactions of climate, land use and plant competition at the local scale. However, for this potential to be fully realised, additional empirical data are required on competitive dynamics of A.artemisiifolia in different crops and ruderal plant communities and its capacity to adapt to local conditions.

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Weedy rice (Oryza sativa) is one of the most widespread and problematic weeds in rice cultivation; it spans the globe and can cause high yield losses. In 2008, seeds of 149 weedy rice populations were collected from the major Italian rice cultivation area. In 2009, these populations were sown in a single field to determine their morphological characteristics, including plant height, flag leaf attitude and length, panicle attitude and length, auricle and node colour, seed weight and size, awn length and germination rates at 0, 10 and 30 days of after-ripening (DAR). Of the collected populations, c. 56% were awned, 17% mucronate and 27% awnless. The morphological characteristics among the awned populations varied widely and displayed the highest average lengths of flag leaf (27.6 cm) and seed (8 mm). Mucronate populations were mainly characterised by small seeds and low germination rates. Awnless populations showed higher germination rates at 30 DAR (20%) and wider seeds (3.7 mm). Awn length and distribution, seed length, 1000 seed weight and germination rates were the most important traits influencing the variability among populations. Awned populations are expected to adapt better to differing environmental and cropping conditions, because of their larger variability.

There is a current need to simulate leaching and runoff of pesticide from rice (Oryza sativa L.) paddies for assessing environmental impacts on a valuable agricultural system. The objective of this study was to develop a model for determining predicted environmental concentration (PEC) in soil, runoff, and ground water through the linkage of two models, rice water quality model (RICEWQ) and vadose zone transport model (VADOFT), to simulate pesticide fate and transport within a rice paddy and underlying soil profile. Model performance was evaluated with a field data set obtained from a 2-yr field experiment in 1997 and 1998 in northern Italy. The predictions of amount of pesticide running off from the paddy field and accumulating in the paddy sediment were in agreement with measured values. Leaching into the vadose zone accounted for approximately 19% of the applied dose, but only a small amount of chemical (<0.1%) was predicted to reach ground water at a 5-m depth due to sorption and transformation in the soil. The permeability of the soil and the water management practices in the paddy field were shown to have a strong influence on pesticide fate. These factors need to be well characterized in the field if model predictions are to be successful. The combined model developed in this work is an effective tool for exposure assessments for soil, surface water, and ground water, in the particular conditions of rice cultivation.