Marija Nešić¹, Dragica Obratov-Petković¹, Dragana Skočajić¹, Ivana Bjedov¹ and Nevena Čule²

¹University of Belgrade – Faculty of Forestry, Kneza Višeslava 1, 11030 Belgrade, Serbia
²Institute of Forestry, Kneza Višeslava 3, 11030 Belgrade, Serbia

e-mail: marija.nesic@sfb.bg.ac.rs

Aster lanceolatus Willd. complex is considered invasive in many European countries, including Serbia. This species is spreading uncontrollably along wet habitats as well as in ecosystems characterised by natural and anthropogenic disturbances. All these habitats function as corridors which facilitate seed dispersal. In order to prevent the spread of invasive plants, it is important to know the biology of invasive species, especially their reproductive ecology. In addition, reproduction affects the ability of plants to colonize new habitats.

In order to investigate the potential of generative reproduction of A. lanceolatus complex, seeds were collected across 13 different localities in Serbia. The influence of four fluctuating temperature regimes on seed germination was investigated. To test the influence of nitrate on seed germination, two KNO₃ concentrations were used: 0.005 M and 0.05 M solutions on four temperature regimes (15/6, 20/10, 30/15 and 35/20 ^oC), whilst distilled water was used for the control. For each treatment, three replicates of 30 seeds were placed in complete darkness or in a 14-hour photoperiod. The influence of the applied treatments were quantified as germinative capacity (GC), germinative energy (GE), and viability percentage. The seed viability was determined using the tetrazolium test.

The results showed that germination increased with increasing temperature. The optimum temperature regimes were 30/15^oC and 35/20 ^oC with approximately 88% germination. The overall effect of KNO₃ on germination was positive. The concentration of 0.05 M KNO₃ had a less pronounced stimulating effect compared to 0.005 M KNO₃. However, the inhibitory effect of both KNO₃ concentrations was expressed in darkness at the highest temperature. The tetrazolium test showed that seed viability was between 93% and 100% at all sites. A. lanceolatus complex seeds showed lower sensitivity to the lack of light during germination. Unexpectedly, the smallest decrease in seed germination from the treatment in darkness was observed at the 15/6^oC temperature in the treatment with 0.005 M KNO₃.

When the introduced species is found in a new habitat, it faces new climatic and habitat conditions, which can be challenging for stand establishment, and species spread further to new habitats. Considering that A. lanceolatus complex often occurs in disturbed sites, seed reaction to changes in temperature, nutrients concentration and light can be one of the determining factors that affect seed germination of this species and, thus, its spread. Although they varied across the localities, the germination parameters showed that generative reproduction could play an important role in the spread of this species. The ability of the seed to germinate in darkness could be significant for the germination ecology of this invasive species since it inhabits disturbed sites, where seed can be buried frequently.