Thermal requirements for seed germination of three invasive alien species (IAS).

Invasive alien species (IAS) have been introduced outside their native sites by humans and becoming part of local flora. The IAS number is strongly increased worldwide during the past two centuries, redefining the classical biogeography boundaries, affecting ecosystem functioning, human health and economies. IAS represent one of the main threats to biodiversity and interconnected ecosystem services. This work aimed to investigate thermal requirements for seed germination of Ailanthus altissima (Mill.) Swingle, Robinia pseudoacacia L. and Phytolacca americana L. Germination tests were carried out at the Germplasm Bank (Botanical Garden of Rome). Seeds were incubated in the dark, and in the light (12 h light/12 h darkness) at three range temperatures (15/6, 20/10 and 30/20 °C). For A. altissima and P. americana cold stratification (4 °C, for 1 month) was investigated as potential factor improving seed germination. Differently, no cold stratification was applied to R. pseudoacacia, which shows pronounced physical dormancy due to an impermeable seed coat. In this case a seed piercing to determine a higher germination was applied. A. altissima and P. americana showed a higher germination rate at 30/20 °C than at 20/10 and 15/6 °C. R. pseudoacacia showed a high germination rate after piercing at 15/6 °C and 20/10 °C, whereas at 30/20 °C a high seed mortality was observed. Expanding knowledge on IAS seed germination is crucial to better understand the invasiveness process. This information can help to find and apply incisive and more appropriate actions to limit the establishment and survival of IAS, whose invasiveness could benefit from climate change in progress.Invazivne tujerodne vrste so na območja zunaj domorodnih območij vnesli ljudje in postajajo del lokalne flore. Število invazivnih tujerodnih vrst je v zadnjih dveh stoletjih močno naraslo po vsem svetu, zaradi česar se na novo določajo klasične biogeografske meje, to pa vpliva na delovanje ekosistemov, zdravje ljudi in gospodarstvo. Invazivne tujerodne vrste so ena od glavnih groženj biotski raznovrstnosti in povezanim ekosistemskim storitvam. Cilj te študije je raziskati toplotne zahteve za klitje semen vrst Ailanthus altissima ((Mill.) Swingle), Robinia pseudoacacia L. in Phytolacca americana L. Testi kalivosti so bili izvedeni v semenski banki (Botanični vrt v Rimu). Semena so bila inkubirana v temi in na svetlobi (12 ur na svetlobi/12 ur v temi) pri treh temperaturnih razponih (15/6, 20/10 in 30/20 °C). Za vrsti A. altissima in P. americana je bila kot potencialni dejavnik izboljšanja kalivosti semen raziskana hladna stratifikacija (4 °C, 1 mesec). Za vrsto R. pseudoacacia, ki ima izrazito fizično dormanco zaradi nepropustne semenske ovojnice, pa hladna stratifikacija, nasprotno, ni bila uporabljena. Pri tej vrsti je bila za določanje večje kalivosti uporabljena perforacija semen. Pri vrstah A. altissima in P. americana je bila pri temperaturnem razponu 30/20 °C ugotovljena večja kalivost kot pri temperaturnih razponih 20/10 in 15/6 °C. Pri vrsti R. pseudoacacia je bila ugotovljena večja kalivost po perforaciji pri temperaturnih razponih 15/6 °C in 20/10 °C, pri temperaturnem razponu 30/20 °C pa je bila ugotovljena velika smrtnost semen. Razvijanje znanja o kalivosti semen invazivnih tujerodnih vrst je ključno za boljše razumevanje procesa invazivnosti. Te informacije lahko pomagajo pri iskanju in uvedbi učinkovitih in primernejših ukrepov za omejitev naselitve in preživetja invazivnih tujerodnih vrst, saj lahko na njihovo invazivnost ugodno vplivajo trenutne podnebne spremembe.