Colonization dynamics of the alien macrophyte Lemna minuta Kunth: a case study from a semi-natural pond in Appia Antica Regional Park (Rome, Italy)
Ceschin, Simona; Della Bella, Valentina; Piccari, Fabrizio; Abati, Silverio
published: Jul 1, 2016
published online: Jun 17, 2016
manuscript accepted: Apr 28, 2016
manuscript received: Nov 1, 2015
ArtNo. ESP141018802001, Price: 29.00 €
Abstract Most studies describing biomass production of Lemna’ species (duckweeds) underline high growth rates of these species under controlled conditions. L. minuta’s growth, as well as its colonizing capability under natural conditions, has never been investigated, despite this species being the most widespread and invasive alien duckweed in Europe. In this study, the colonization dynamics of L. minuta were analysed through a 5 month field-experiment carried out in a semi-natural pond of 26.3 m2 in the city of Rome. Variations in plant coverage (m2), biomass produced (g) and Relative Growth Rate (RGR, day–1), show that L. minuta has an growth of exponential type, consisting of three main phases: (1) an initial phase (40 days), in which L. minuta grows moderately by covering just under 15 % of the pond surface; (2) an exponential phase (45 days), in which the duckweed grows intensively, until it completely covers the entire pond surface with a monolayer floating population; (3) an apparently stationary phase perpetuated in time, in which, instead, the species continues to grow in biomass, giving rise to a dense multilayer population 2.5 cm thick. L. minuta was able to colonize the entire pond surface in a few months of experiment, increasing its total biomass over 600 times respect to that initial. This underlines the species’ high biomass production in natural conditions. The RGR of L. minuta estimated at the end of the experiment amounts to 0.041 day–1 (0.046 day–1, 0.006 day–1, 0.126 day–1 as average, minimum and maximum RGR, respectively) more than double of that calculated in similar conditions for the native congeneric L. minor, showing a higher colonization capability of the alien species respect to the native ones. The characterization of the growth dynamics in field of the alien L. minuta provides information that could be useful for a better planning of management programs of natural wetlands invaded by this alien species, also with respect to its invasion control. Our findings suggest that in lentic environments, it is necessary to remove the species every 30 – 40 days for controlling this duckweed and prevent its future outbreaks locally. However, the complete removal of an entire L. minuta population from a natural site can result difficult and demanding but, combining a physical control of L. minuta with a subsequent biological one, it could make more effective the eradication action of the species from a site.