Reflectance characteristics of flowers as a criterion for invasiveness of Erigeron annuus (L.) Pers.

The invasiveness of alien plants is determined by a complex of functional features, among which the impact of phytoinvasions on the relationships between native plants and pollinators is noted. Flowers of invasive plants are characterized by increased attractiveness to pollinators, which ensures significant seed production, population growth and expansion. To explain such a trend, it is necessary to identify the differences in the flowers of invasive plants. The results of a comparative study of the reflectance spectra and colorimetry of flowers of the invasive species Erigeron annuus (L.) Pers. (annual fleabane) and the native species Achillea submillefolium Klokov et Krytzka (almost common yarrow) are presented. Selection of border flowers with white color of co-flowering plants was carried out in the recreation area of Botanical Garden of Oles Honchar Dnipro National University. It was established that the defining feature of the reflectance spectra of E. annuus flowers compared to A. submillefolium flowers is an increase in the maximum intensity of UV-absorbing flavonoids in surface tissues. The identified feature corresponds to the maximum sensitivity of the UV photoreceptor of such a common pollinator as Apis mellifera L. The characteristics of the differential reflectance spectrum of flowers of co-flowering plants were determined as markers of the color contrast between invasive and native species and an attractive signal for the pollinator's UV receptor. The flowers of the studied plants were also characterized by a specific set of colorimetric parameters. According to the data of differential colorimetry, the relative contribution to the integral value of the color difference of the flowers of the compared species was established for the component differences in lightness and chroma. In addition to attractiveness, the light-absorbing properties of flavonoids provide another important function – photoprotective. In the flowers of E. annuus, apigenin, luteolin and their glycosides predominate among flavonoids, for which the presence of two bands with high absorption capacity can provide a significant protective capacity against UV-A and UV-B radiation. Therefore, the increased localization of UV-absorbing flavonoids in the surface tissues of flowers of invasive plants may mean a simultaneous increase in attractiveness and photoprotective ability compared to native species. Such a tendency should be considered as an adaptive strengthening of the reproductive system of an invasive species. The obtained results confirm the role of phenolic compounds in increasing the competitiveness of invasive plants according to the shifting defense hypothesis. Since the biomass of E. annuus is distinguished by a high content of biologically active phenolic compounds, the reflectance spectroscopy in the visible range and colorimetry used by us can be applied to the development of the modern direction – the expansion of the raw material base of medicinal plants due to the use of invasive species.