CANCELLED - The competitive response of Panicum virgatum cultivars to non-native invasive species

Background/Question/Methods

Historically, the Tallgrass Prairie (TGP) was the largest ecosystem in North America. Since European settlement, the TGP has declined to less than 0.01%. Three historical factors that were important natural processes for grassland communities were climate, ungulate grazing, and fire; however, non-native invasive species are a recent phenomenon that threatens the integrity of surviving TGP communities. TGP primarily consist of C₄ grasses, which exhibit intraspecific ecotypic variation. Ecotypes are the basis of the numerous cultivars, which may impact the success of prairie restoration. In this study, the effects of three invasive species (Bromus inermis, Schedonorus phoenix, and Poa pratensis) on two lowland and three upland cultivars of the dominant C₄ grass Panicum virgatum was tested. A simple pair-wise greenhouse experiment was established. Cultivars were sown as a monoculture or as a mixture of the cultivars or with one of three invasive species. Pots were subjected to two water treatments (low and high). Three replicates of each treatment combination were established. Response variables (height, number of leaves, tiller density, and biomass of P.virgatum) and resources (soil moisture and light intensity) were measured over a seven-month period.

Results/Conclusions

Over the 213 days of the experiment, performance of the different P. virgatum cultivars were differentially affected by the three invasive species, especially the performance of the Kanlow (lowland) and Blackwell (upland) cultivars (P<0.0001). Soil moisture affected the performance of P. virgatum in the presence of only one invasive (Bromus inermis, P=0.03) irrespective of cultivar source. There was an interaction between the P. virgatum cultivars and time affecting light intensity (P=0.07). Different cultivars affected the light intensity at the soil level differently, for example, light intensity under Trailblazer (upland) decreased between day 136 and day 157 whereas light intensity under other cultivars did not change. Soil moisture was lower under lowland cultivars than upland cultivars (P=0.03). After 208 days, cultivars Alamo (lowland) and Trailblazer (upland) had been completely displaced by invasive species. The results of this greenhouse study suggest that invasive species may have an affect on the particular cultivar that is sown in a prairie restoration.