Vegetative regeneration capacities of five ornamental plant invaders after shredding

Synflorescence regeneration after cutting in Solidago ×niederederi (Asteraceae), a hybrid between invasive S. canadensis and native S. virgaurea

Solidago ×niederederi, a natural hybrid between invasive S. canadensis and native S. virgaurea, is considered as naturalized alien taxon in Europe. In this study, we conducted a field experiment on the regeneration ability of S. ×niederederi after cutting off its synflorescences (panicles with capitula). The regeneration of synflorescences occurred in 79.6% of the examined shoots (ramets) of the hybrid. After regeneration shoots were significantly shorter and formed shorter, narrower and less branched synflorescences. Moreover, the number of capitula was significantly lower after regeneration as well as number of disc flowers and pollen viability. The obtained results suggest that the hybrid has a high ability of synflorescence regeneration after cutting and one-time cutting at high level during flowering is not effective method to control the hybrid in the wild.

Enforced Clonality Confers a Fitness Advantage

In largely clonal plants, splitting of a maternal plant into potentially independent plants (ramets) is usually spontaneous; however, such fragmentation also occurs in otherwise non-clonal species due to application of external force. This process might play an important yet largely overlooked role for otherwise non-clonal plants by providing a mechanism to regenerate after disturbance. Here, in a 5-year garden experiment on two short-lived, otherwise non-clonal species, Barbarea vulgaris and Barbarea stricta, we compared the fitness of plants fragmented by simulated disturbance ("enforced ramets") both with plants that contemporaneously originate in seed and with individuals unscathed by the disturbance event. Because the ability to regrow from fragments is related to plant age and stored reserves, we compared the effects of disturbance applied during three different ontogenetic stages of the plants. In B. vulgaris, enforced ramet fitness was higher than the measured fitness values of both uninjured plants and plants established from seed after the disturbance. This advantage decreased with increasing plant age at the time of fragmentation. In B. stricta, enforced ramet fitness was lower than or similar to fitness of uninjured plants and plants grown from seed. Our results likely reflect the habitat preferences of the study species, as B. vulgaris occurs in anthropogenic, disturbed habitats where body fragmentation is more probable and enforced clonality thus more advantageous than in the more natural habitats preferred by B. stricta. Generalizing from our results, we see that increased fitness yielded by enforced clonality would confer an evolutionary advantage in the face of disturbance, especially in habitats where a seed bank has not been formed, e.g., during invasion or colonization. Our results thus imply that enforced clonality should be taken into account when studying population dynamics and life strategies of otherwise non-clonal species in disturbed habitats.