Resistance of seedlings of native and alien species of the genus Bidens (Asteraceae) from different geographic populations to the action of heavy metals.
One approach to assessing the competitiveness of invasive species is a comparative analysis of the morphological, physiological, and reproductive traits of this species with native species of the same genus. The invasive species Bidens frondosa L. from the Asteraceae family, included in the list of the 50 most common and most aggressive invasive species in Europe, occupies the same ecological niche as the native species B. tripartita L., and displaces it from natural habitats. There is an obvious and growing interest in the sustainability of B. tripartita and B. frondosa in extreme conditions of existence, one of which is the action of heavy metals. Our research was performed in laboratory conditions with seedlings that developed from seeds collected from populations of the Upper and Middle Volga region. The seeds were germinated in Ni2+ and Cu2+ solutions at various concentrations. At the end of the experiment, morphometric parameters were measured and the index of tolerance was determined. Seedlings from different populations under the influence of nickel ions developed at concentrations of 1-50 mg/l, under the influence of copper ions - at 1-100 mg/l. The nickel and copper ions had the greatest toxic effect on the growth and development of the root system - at 25 mg/l and above, the main root was completely necrotic, while the action of copper ions simultaneously increased the number of adventitious roots. The tolerance index ("root test") under the action of nickel ions was higher among the seedlings from the population of the Middle Volga region, while under the action of copper ions there were no significant differences among the seedlings from different populations. However, it decreased with the action of both heavy metals at a concentration of 10 mg/l. High concentrations of both metals significantly reduced the length of the hypocotyl, cotyledon, and the true leaf. It was also found that copper ions are more toxic for the root system (main root and adventitious roots), nickel ions - for above-ground organs (hypocotyl, cotyledons, and true leaves). We noted differences between the populations to the action of nickel and copper. From the population of the Upper Volga region, the seedlings of B. frondosa were more stable. For seedlings from the population of the Middle Volga, a smaller toxic effect was confirmed for B. tripartita. It can be assumed that the resistance of B. frondosa to the action of heavy metals as a stress factor in the Upper Volga region is one of the reasons for the suppression of B. tripartita by the invasive species.