Do seeds of invasive plants persist longer in the soil than those of non-invasive alien species?

Invasive alien plants negatively affect biodiversity and ecosystem functioning. Among reproductive traits found to promote invasiveness, rapid dispersal and production of seed persisting in the soil for a long time have been shown to play an important role. To test this association experimentally, we conducted a burial experiment to find out if there are differences in seed persistence between invasive and non-invasive alien plant species. Seed of 73 species that are alien in the Czech Republic (35 invasive and 37 non-invasive) were collected in the field, tested for viability and buried in nylon bags in the soil in a common garden at the Institute of Botany, Průhonice. Seeds were exhumed once a year (spring 2014, 2015), and the fraction of germinated or decayed seeds, and of non-germinated but viable seeds, was determined in each sample. This allowed us to ascertain seed persistence/viability after 1.5 and 2.5 years of burial in the soil. We found that invasive and non-invasive species differed in seed persistence. Seeds of all invasive species were viable or germinated to some percentage after 1.5 year of burial in the soil, while 16% of non-invasive species did not survive during this burial period. Moreover, the majority of invasive species showed a high seed survival percentage (survival category 75-100%), while only low percentage of non-invasive species germinated or were viable after this period in this survival category. After 2.5 years of burial in the soil, the majority of invasive species showed a seed survival percentage ranging from 5-25%, while non-invasive species were distributed rather evenly among all other survival percentage categories, with only 5% species in highest survival category. These preliminary results suggest that invasive species tend to persist longer in the soil and have thus potential to form larger and long-term persistent soil seed banks then non-invasive species.