Zygmunt Dajdok1, Ludmiła Polechońska2, Agnieszka Klink2, Małgorzata Dambiec2, Edyta Gola3 and Michał Gleńsk4
1Department of Botany, Institute of Environmental Biology, University of Wrocław, Kanonia 6/8, 50-328 Wrocław, Poland
2Department of Ecology, Biogeochemistry and Environmental Protection, University of Wrocław, Kanonia 6/8, 50-328 Wrocław, Poland
3Department of Plant Developmental Biology, Institute of Experimental Biology, University of Wrocław, Kanonia 6/8, 50-328 Wrocław, Poland
4Department of Pharmacognosy, Wrocław Medical University, Borowska 211a, 50-556, Wrocław, Poland
Communities of ephemeral plant species growing on the borders or bottoms of water reservoirs are classified in Europe as indicators of a protected habitat “oligotrophic to mesotrophic standing waters with vegetation of Littorelletea uniflorae and/or Isoëto-Nanojuncetea 3130”, with many regionally threatened species (e.g. Lindernia procumbens, Elatine spp., Eleocharis ovata or Coleanthus subtilis). Importantly, plant species alien to Europe, which reveal invasive properties, such as Veronica peregrina, can be a threat for these communities. In SW Poland, this species appears massively, with hundreds of thousands of individuals in some places, and colonizing mainly the exposed bottoms of fishponds. We aimed to evaluate Veronica peregrina in terms of the traits that may enable effective competition with other plants, such as (i) habitat preferences, (ii) the number of seeds produced outside of the native range and germination capacity, and (iii) the phytotoxic potential of the species.
The study covered 11 dried ponds in three fishpond complexes located in Lower Silesia, SW Poland. In each studied fishpond, the sample plots (1 × 1 m2) were designated along linear transects. All vascular plants growing within these plots were listed and their cover was determined. Within each plot, a top layer of bottom sediment was randomly sampled (10 × 10 cm2, depth of 0–5 cm). Sediment samples were used to determine the pH and concentrations of macroelements (N, P, K, Ca, Mg, Na). Additionally, all specimens of V. peregrina were counted and collected in each sampling plot in order to determine the biomass and to identify allelopathic substances present in the plants tissues. Furthermore, in three of the studied fishponds, samples of V. peregrina were collected for biometric studies: the plant height, number of branches and fruit (capsules) per plant, and the number of seeds in each capsule were determined.
Our results showed that populations of Veronica peregrina were more numerous on sites characterized by sandy substrates with a low content of N, K, Mg, Ca and Na and a high content of P. In such habitat conditions, V. peregrina covered up to 90% of the stand, while on muddy sediments, rich in macroelements, other species prevailed, limiting the V. peregrina cover to 10-40%. Biometric analyses showed that unbranched individuals with an average shoot length of 88.9 ± 45.3 mm predominated in the studied populations. The average fruit number was 6.25 ± 5.3 per plant, while the average number of seeds in the capsule was 71.4 ± 24.9. The presence of allelopathic compounds in V. peregrina tissues was confirmed by biochemical analysis, while the biotest showed that the aqueous extract of dried plant material inhibited the germination of Sinapis alba seeds.
The obtained results prove that the chemical composition of the bottom sediments affects the population density and biomass production of V. peregrina. Importantly, this species can play a key role as a component of ephemeral plant communities inhabiting periodically exposed water banks, e.g. due to its phytotoxic activity. However, the effectiveness of its impact on the particular species in these communities requires further research