Germination patterns and seedling growth of congeneric native and
invasive Mimosa species: implications for risk assessment
Abstract
Comparisons of plant traits between native and invasive congeners are
useful approaches for identifying characteristics that promote
invasiveness. We compared germination patterns and seedling growth of
locally sympatric populations of native Mimosa himalayana and two
varieties of invasive M. diplotricha (var. diplotricha and var. inermis)
growing in south-eastern Nepal. Seeds were germinated under 12h
photoperiod or complete dark, low (25/15°C day/night) and (30/20°C) high
temperatures, different water stress levels, and soil depths. Plant
height, biomass allocations, and relative growth rate (RGR) of seedlings
were measured. Invasive M. diplotricha had higher germination
percentage, rate, and shorter germination time than native species.
Germination of both congeners declined as water stress increased, but
the decline was more pronounced in native species. Seedling emergence
declined with increasing depth in all taxa. The seedlings of invasive
species were taller with higher leaf number and allocated greater
proportion of biomass to shoot, while the native congener allocated
greater biomass to root. The RGR was nearly twice as high in invasive
species as it was in native congener. Seedling height and number of
leaves were always higher in invasive than in native and the
native-invasive differences increased over time. Better germination and
higher growth performance of invasive species than congeneric native one
suggests that seed germination and seedling growth can be useful traits
for the prediction of species’ invasiveness in their introduced range
during risk assessment process.