A comparative study on phenotypic plasticity of native vs invasive purple loosestrife (Lythrum salicaria L, Lythraceae)

We examined the differences in the response to environmental change (phenotypic plasticity) between invasive (North American) and native (German) plants of Lythrum salicaria (purple loosestrife). This was done by an in-field common garden study with a split-plot design with experimentally manipulated water and nutrient level conditions. Data were collected for a total of eight traits related to life history (number of dates to first flowering), plant size / architecture (height, number of secondary branches, number of stems from root, and leaf area), and fitness (number of flowers, reproductive: total biomass ratio, and total biomass). Plants from invasive provenances were found to be significantly different from plants from native provenances in phenotypic plasticity and plant performance. Generally, invasive plants exhibited greater height and leaf area than native plants across all treatments. Native plants, in contrast, flowered earlier than invasive plants, thus allocating more resource to flower production. However, given increased level of nutrients, invasive plants outperformed native plants in total biomass and number of flowers. Among invasive plants, lately-established populations (Iowa and Michigan) were likely to possess greater biomass, number of branches and flowers than early-established populations (New Jersey). Our results indicate that invasive and native purple loosestrifes have evolved different life history strategies favoring vegetative production and reproductive fitness, respectively.