Older populations of the invader Solidago canadensis exhibit stronger positive plant-soil feedbacks and competitive ability in China

PREMISE
The enemy release hypothesis predicts that release from natural enemies, including soil-borne pathogens, liberates invasive plants from a negative regulating force. Nevertheless, invasive plants may acquire novel enemies and mutualists in the introduced range, which may cause variable effects on invader growth. However, how soil microorganisms may influence competitive ability of invasive plants along invasion chronosequences has been little explored.
METHODS
Using the invasive plant Solidago canadensis, we tested whether longer residence times are associated with stronger negative plant-soil feedbacks and thus weaker competitive abilities at the individual level. We grew S. canadensis individuals from 36 populations with different residence times in competition versus no competition and in three different types of soils: (1) conspecific rhizospheric soils, (2) soil from uninvaded patches, and (3) sterilized soil. For our competitor treatments, we constructed synthetic communiti...