Ludwigia hexapetala is an alien aquatic plant considered highly invasive in Europe since it alters freshwater habitats by forming dense mats both in water and along banks, outcompeting natives. Ludwigia effects on the native carnivorous plant Utricularia australis were investigated here. A 21-day indoor experiment was performed by setting up some separate tests in which Utricularia was made to grow both alone (control tests) and together with Ludwigia (arena tests). Water chemical and physical parameters and growth and morphological traits of Utricularia and Ludwigia were analysed weekly. Water samples were also analysed by UV-visible spectra to verify allelochemical (quercitrin) production by Ludwigia. In arena tests, oxygen concentration and pH were lower and conductivity higher than in control tests. Utricularia grew significantly less in arena tests in both shoot length and internode number, and its fresh weight, trap number and internode length decreased more than the control. Quercitrin was found only in arena tests as an allelochemical product released by Ludwigia. Overall, this study demonstrated Ludwigia significantly alters water parameters and negatively affects the growth of Utricularia, showing aggressive and competitive behaviour against this native species. Such evidence suggest that the widespread of L. hexapetala can represent a serious threat to the conservation of native plant diversity occurring in the freshwater habitats it invades.

Microplastics are widely spread in aquatic environments. Although they are considered among the most alarming contaminants, toxic effects on organisms are unclear, particularly on freshwater plants. In this study, the duckweed Lemna minuta was grown on different concentrations (50, 100 mg/L) of poly(styrene-co-methyl methacrylate) microplastics (MP) and exposure times (T0, T7, T14, T28 days). The phytotoxic effects of MP were investigated by analyzing several plant morphological and biochemical parameters (frond and root size, plant growth, chlorophyll, and malondialdehyde content). Observations by scanning electron microscope revealed MP adsorption on plant surfaces. Exposition to MP adversely affected plant growth and chlorophyll content with respect to both MP concentrations and exposure times. Conversely, malondialdehyde measurements did not indicate an alteration of oxidative lipid damage in plant tissue. The presence of MP induced root elongation when compared to the control plants. The effects of MP on L. minuta plants were more evident at T28. These results contribute to a better understanding of MP’s impact on aquatic plants and highlight that MP contamination manifests with chronic-type effects, which are thus detectable at longer exposure times of 7 days than those traditionally used in phytotoxicology tests on duckweeds.

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