Variation in germination and growth among populations of an invasive plant, Alliaria petiolata (M. Bieb) Cavara and Grande

There are many different reasons why a non-native plant species might become invasive in a novel habitat. Some studies have focused on trying to determine the genetic structure of an invasive species. Other studies have investigated whether they are either more phenotypically plastic and thus able to utilize many different habitats, or it they have adapted to the new habitats before and during their range expansion. The invasive biennial Alliaria petiolata (M. Bieb) Cavara and Grande has been shown to be both phenotypically plastic and adapted to its introduced range. In this this study I investigated differences in survival, growth and reproduction and for multiple source populations of A. petiolata grown together in novel environments not experienced by any of the source populations. I conducted a common garden study as well as a coldstratification germination study, utilizing seeds collected from source populations located along the species’ invasive range. For the common garden experiment, seeds were collected in North Carolina, Tennessee, Virginia, Maryland, Pennsylvania and New York and placed in two garden plots at two different elevations, Franklin, NC (elevation 670m) and Highlands, NC (1190m). The cold stratification experiment used seeds from Asheville, North Carolina; Cleveland, Ohio; and Bronx, Cold Spring and Ossining, NY. These seeds were placed in moist soil and cold-stratified at 3°C for a short (66 days), medium (80 days) and long (100 days) cold stratification season. The results of the common gardens study showed differences in responses among populations in numerous traits: seed and silique production, silique abortion, survival, number of stalks and biomass. When means were sorted from north to south with a calculated equivalent bioclimate using Hopkins Bioclimatic Law, adaptation to climate was potentially observed with a greater number of stalks in the southern equivalent bioclimate in the low elevation gardens. The seeds from two northern populations of Cleveland, Ohio and New York (“H”) showed the highest germination for the short stratification season of 1584 chilling hours, with both over 20% germination. The southern-most population in Asheville, North Carolina had the highest germination (86%) for the medium stratification season of 1920 chilling hours. As previous studies have also shown, germination was nearly complete with 2400 hours of cold-stratification. There may be adaptation to climate among the populations studied for number of stalks, but no other traits show any patterns with regards to climate. A few traits such as seed production, number of siliques and survival, showed similar means among the northern populations, and may indicate genetic relationships among populations along the southward invasion route of A. petiolata’s range. This study supports the conclusion that A. petiolata is a habitat generalist, but that there is some variation in growth, reproduction and survival