The effect of site conditions and type of ramet clusters on sexual and asexual ramets of Solidago × niederederi (Asteraceae)

Spontaneous hybrids between alien and native plant species are alien taxa and they threaten native biodiversity due to their high competitive ability or introgression. Thus, we tested the effect of soil conditions, elevation and type of ramet clusters (clonal clumps of shoots) on sexual and asexual ramets of Solidago × niederederi, a hybrid between the invasive alien S. canadensis and the native S. virgaurea. We also tested the relationships between the size of sexual ramets and habitat conditions in the hybrid and its parental species, based on ten sites in NE and S Poland, respectively. The hybrid and its parental species occurred on mineral soils with a wide range of textures (sand, loamy sand, sandy loam, silty loam and loam) and pH (from strongly acidic to slightly alkaline). Sexual ramet clusters dominated in S. × niederederi populations, while the total number of ramets was highest in mixed ramet clusters. The cluster × site interaction had a significant effect on the length and biomass of sexual ramets in hybrid populations. Moreover, we found a significant effect of the taxon × site interaction in the case of biomass of sexual ramets and synflorescences (capitula arranged in panicles). Based on the biomass of sexual shoots and synflorescences, the competitive abilities of the hybrid may be more or less similar to S. canadensis or S. virgaurea albeit depending on site conditions.