The problem of invasive alien plants in European urban settings: testing non-invasive cultivars and species as alternatives to Ligustrum sinense Lour.

Cities are hotspots for the introduction establishment, growth, and subsequent spread of invasive alien plant species (IAPs); however, they can also have an important role in biodiversity conservation. The IAPs invasions are a major threat to biodiversity, human well-being, and the economy, and may be further exacerbated under climate change. Some ornamental plants, popular in urban green spaces, have become invasive, such as Ailanthus altissima (Mill.) Swingle, Buddleja davidii Franch., Ligustrum sinense Lour., Lonicera japonica Thunb., and Prunus laurocerasus L. The floriculture industry’s plant trade has been recognized as one of the main pathways for the introduction of IAPs worldwide. The purpose of the research, as part of the Italian National Biodiversity Future Center (NBFC) project, is to provide suitable ornamental alternatives, including non-invasive cultivars, and to promote the use of native plants. The contribution focuses on the evaluation of two possible alternatives to L. sinense Lour. (IAP): L. vulgare L. (European native), and L. japonicum Thunb. ‘Texanum’ (non-invasive ornamental cultivar). In an experimental trial, the three species were compared in their responses in growth and morpho-physiological traits to salt and water stresses under climate-controlled conditions. A total of 270 plants, approximately 25 cm in height, were cultivated in pots (diameter 9 cm) in March 2024 situated inside a growth chamber. The plants underwent one of two treatments of NaCl solutions (150 mM and 300 mM) or deionized water (control). Additionally, two irrigation levels were applied, specifically 30 and 60% of field capacity, while the control group received 90% of the field capacity. Preliminary results will highlight plant growth physiological responses, and overall performance, serving as valuable indicators to assess the potential of these species as alternatives for the development of sustainable urban horticulture.