Winter abundances of naked amoebae in the soil system of the invasive species Japanese knotweed (Fallopia japonica) with comparative data from adjacent sites

Among the most prolific invasive plant species posing threats to the ecological balance of ecosystems in North America and Europe is Japanese knotweed (Fallopia japonica). In order to identify the potential role of protists in the invasive capacity of Japanese knotweed the winter abundances of naked amoebae in soils from three roadside thickets of Japanese knotweed were compared to nearby non-invaded sites. Japanese knotweed soils had higher abundances (t = 5.43, df, 16, p < 0.001) of amoebae than comparison sites. This is one of the first studies to document higher abundances of soil naked amoebae associated with an invasive plant, and may indicate more generally that below-ground abundances of amoebae can promote soil fertility and support the successful adaptation and expansion of some invasive plant species. Moreover, analysis of encysted vs. trophic forms of naked amoebae in the winter soil, provided evidence of freezeresistant, amoeba resting cells in soil samples from the natural environment in support of prior findings that were based solely on laboratory experimental evidence. Overall, high densities of naked amoebae in the winter soils of Japanese knotweed, some as resting cells capable of forming rapidly activated trophic stages, likely increase soil fertility and strengthen the species’ invasive capacity.