Allelopathy of globally successful invader Conyza canadensis L.

Abstract

The globally successful invader C. canadensis is the first species to colonise the sandy levees beside the rivers into new areas and, owing to high levels of seed production and in particular its allelopathic effect, it completely dominates the other species in the ruderal phytocoenosis. The content of total phenolics and phenolic acids varies, following the order: vegetative plant parts > dead plant parts > sandy soil under C. canadensis. Water leachate and soils inhibited seed germination and seedling growth of the neighbouring herbaceous plantsto varying degrees: vegetative parts > dead parts > sandy soil, which is directly related to the content of total phenolics and phenolic acids in them. Secondary metabolites, above all phenolic compounds released from its vegetative organs, reach the sand under it, where they have a negative effect on seed germination and seedling growth of neighbouring herbaceous plants, reducing their abundance and cover. The dynamics of allelopathically significant phenolic compounds in C. canadensis L. tissues and in the sandy soil have a marked seasonality and coincide with certain phases in plant development. The highest amount of phenolics in the tissue was measured during the phase of plant elongation and intensive growth, and again during the phase of fruit abscission and plant decline. It can be seen that the level of free acids in the soil under C. canadensis, increases dramatically between March, when the plants are in the form of rosettes, 1-2 cm in diameter, and July, the beginning of flowering. In these months free phenolic acids account for as much as 73.7% of the total free phenolics in the soil. The percentage of soil bound phenolic acids gradually increases between April, when the plants are in the form of larger rosettes, 5-10 cm in diameter, and August (in full flower and beginning of fruiting), when their maximum level (43.5%) is reached. Phenolic acids can serve as reliable bioindicators of phenolics metabolism and turnover, starting from their biosynthesis in plant tissues to their incorporation into stable fractions of soil humus. Also, they show the level of improvement in substrate quality for further plant colonisation in comparison to sands. An important role in the spread of this invasive species into new areas and its domination over native species is played by phenolic compounds as the most abundant group of allelochemicals. These exert regulatory roles in many processes, not only in plants themselves, but as well in the ecosystem as a whole.