Grasslands cover 35% of earth’s land surface, provide many essential ecosystem services, and play an important role in driving global biogeochemical cycles. One of the greatest current threats to these ecosystems is invasion by non-native species. While the underlying biological mechanisms facilitating non-native species invasion are still unknown, there is growing recognition that alterations in belowground processes may play fundamental roles in the success of invasive species. The objectives of our study were to assess above- and belowground consequences of invasion by a non-native warm-season grass, Bothriochloa bladhii. We established four replicate 0.25 m plots in invaded and adjacent non-invaded tallgrass prairie sites at Konza Prairie Biological Station, Manhattan, KS. Invaded plots were fertilized annually for 20 years with N; P; or not fertilized (control). In each replicate plot, above- and belowground biomass and plant species composition were assessed. Soil biotic parameters included relative abundance of soil microbial functional groups (phospholipid and neutral lipid fatty acid analyses) and intra-radical mycorrhizal hyphal abundance. Soil abiotic parameters included plant-available N and P, and soil aggregate distribution. Our overall goal was to assess potential alterations in soil systems following invasion by non-native species to facilitate successful restoration of grassland ecosystems.
Plant species richness of the non-invaded prairie averaged 14 species per m2 and was significantly greater than invaded sites. In fact, the invaded sites we assessed in this study were monocultures of B. bladhii, regardless of fertilization treatment. Soils of P-fertilized plots contained significantly greater levels of plant-available P (PO4), compared to N-amended or control plots, or adjacent prairie. However, N fertilization did not affect concentrations of NO3 or NH4. Although higher concentrations of plant-available N was not observed in N-fertilized soils, aboveground and total biomass production were greater in the N-amended invaded areas, compared to control, P-amended, or adjacent native tallgrass prairie sites. However, allocation to root production was lowest in N-fertilized plots, resulting in significantly lower root/shoot ratio, compared to P-fertilized, control, or native plots. Our preliminary analyses of soil microbial community assessments indicate invasion by the non-native grass altered total microbial biomass and shifted relative abundance of microbial functional groups.