Congratulations to Simona Paolacci who submitted her PhD thesis on October 7, 2016. Simona’s research focused on the question why some aquatic plants become highly invasive outside their natural distribution area. This is an important question as alien aquatic plants are a major threat to biodiversity and a considerable amount of money is spend on their management and control. Being able to recognise potentially invasive species before they are widely distributed in their new environment may facilitate management, and reduce management costs. In her PhD research, Simona compared growth of the native (in much of Europe, Asia, Africa and north America) species Lemna minor, with the alien, invasive (in much of Europe) species Lemna minuta. These two species are closely related, and are in fact visually difficult to distinguish from one another. Physiological and morphological parameters were used to quantify the performance of the two species and interpret the growth strategies adopted. It was found that L. minuta has generally a higher growth rate than L. minor. Especially at high light intensities L. minuta outgrows the native species. In contrast, L. minor grows faster in shady conditions. Thus, L. minuta is better at taking advantage of resources, such as light, but also phosphate. Such knowledge will help inform monitoring for the invasive species in areas not yet colonised.
Simona’s work also showed that alien L. minuta does not appear to exclude L. minor from natural habitats, despite outgrowing the native species during the summer. The reason for this appears to be the winter period which “resets” the balance between native L. minor and the alien L. minuta. The native species is the first one to re-start its growth after the winter in accordance with the tolerance to low temperatures observed under laboratory conditions. Thus, survival of winter conditions appears to be a major consideration when considering the competitive balance between native L. minor and alien L. minuta.
Simona’s PhD research was funded by the Irish Research Council (IRC), and jointly supervised by Prof. Marcel Jansen and Dr. Simon Harrison.