Can asexual reproduction by plant fragments help to understand the invasion of the NW Iberian coast by Spartina patens?

Abstract

A common characteristic of alien plant invasions is the founder effect, resulting in low genetic variability and thus limited sexual reproduction. In some circumstances, asexual reproduction helps to overcome this hindrance, especially in coastal areas exposed to extreme weather events that help produce plant fragments acting as propagules. Spartina patens (Aiton) Muhl (Poaceae) is an alien invader colonizing most saltmarshes in NW Iberia (Spain and Portugal). The extent of the invasion in the area is quite large, but it remained unnoticed until recently due to the absence of flowering shoots that would have allowed for quick detection and identification. Here we ask whether vegetative propagules can help to understand the extensive spread of the invader. Both propagule characteristics (number and diameter of nodes) and environmental conditions (season and sediment covering) influenced the sprouting rate. In winter, around 30% of the fragments sprouted and produced short shoots of on average 2.8 cm tall. In spring, 40% of the fragments sprouted and produced larger shoots of 13.3 cm tall. Thus, even when conditions are harsh, this species can sprout from plant fragments abundantly. These results may help explain the success of this species invading NW Iberia, and suggest that asexual reproduction plays a role in the invasion by S. patens. Also, eradication techniques which can release plant fragments should be avoided as a measure to control the invasion of this plant.