As much as 99% of North America’s tallgrass prairie has been lost. The remaining tallgrass prairie faces the continuous threat of ecosystem degradation through invasions by non-native plant species. Of critical concern for conservation, restoration of native biodiversity has been met with little success following eradication of non-native plants. While much attention has been placed on aboveground processes, considerably less research has focused on assessing the role of belowground microbial processes in restoration success.
Our research was conducted at Konza Prairie Biological Station in Manhattan, KS, USA. Several areas of this station have become invaded with 95-100% of a non-native C4 grass (Bothriochloa bladhii). These areas received regular applications of glyphosate for eight years, in attempts to control and eradicate B. bladhii. However, attempts to revegetate with native species have been unsuccessful. To assess mechanisms that prevent survival of native species and to improve native species establishment, we established six replicate plots of each of the following four treatments: (a) freshly collected prairie soil (intact native microbial communities) with native prairie seeds; (b) autoclaved prairie soil (absence of native microbial communities) with native prairie seeds; (c) non-inoculated (no soil amendments) with native prairie seeds; and (d) non-inoculated/non-seeded control.
No native seedlings were observed in non-seeded plots. Therefore, recruitment of seed from adjacent native grasses and forbs did not occur. While inoculation with native soil (intact native microbial communities) did not improve germination, the presence of soil microbes significantly improved native species seedling survival (41%), compared to sterile soil or no soil amendments (12-18%). Of important conservation concern is that repeated applications of glyphosate did not successfully eradicate the invasive plant in any of our restoration plots. However, inoculation with native microbial communities significantly decreased re-establishment of B. bladhii; at the end of the growing season, plots receiving native soil consisted of 33% B. bladhii (% cover), compared to 70% in plots receiving no soil inoculum. Our study indicates restoration success of degraded grasslands can be improved by additions of native plant seeds in combination with native soil microbial communities.