As much as 99% of North America’s original tallgrass prairie has been converted to anthropogenic uses such as row crop agriculture, and remaining portions of this endangered ecosystem are threatened by human activities. Restoration of native biodiversity is critical for ecosystem resilience, but efforts to establish native species in degraded sites are often expensive and unsuccessful. When soils are degraded, alteration of native soil microbial communities may contribute to unsuccessful restoration outcomes. Re-establishment of native beneficial soil microbes, such as arbuscular mycorrhizal (AM) fungi can enhance establishment and survivorship of native plants through increased uptake of water and nutrients. Therefore, grassland restoration efforts may benefit from inoculation with commercially available AM fungi; however, it is critical to assess these commercial products prior to widespread use in restoration projects.
We conducted a controlled growth room experiment to assess biomass production of eleven plant species, including native and non-native species, following inoculation with commercial AM fungal products. We quantified above- and belowground biomass and AM fungal root colonization for each plant species grown in native grassland soil containing only naturally occurring AM fungi (i.e., control treatment) or native grassland soil inoculated with one of six different commercial AM fungal inoculants.
Results/Conclusions
We hypothesized commercial inoculant products would promote plant productivity, compared to native AM species. However, our results suggest commercial AM inoculants generally had no significant effect, or even negatively affected native plant biomass, while increasing the growth of some invasive plant species. While soil utilized in this experiment had low/moderate plant-available N and P (23 and 9 mg kg-1, respectively), two of the commercial products included a substantial amount of additional N and/or P (>100 and >300 mg kg-1, respectively), which may have been partially responsible for increased invasive plant growth. Mycorrhizal root colonization was assessed as an indication of symbiotic activity, and preliminary results indicate similar or greater AM fungal root colonization of plants grown in non-amended (control) soil compared to plants treated with commercial products. We conclude inoculation with commercial AM products may not be necessary for native grassland restoration, presumably as local AM fungi confer similar or greater benefits compared to commercial products. If so, restoration practitioners need not use limited financial resources on commercial AM inoculants if local AM fungal propagules are already present. In fact, use of commercial inoculants could result in competitive advantage for certain non-native species, threatening the biodiversity of restoration sites.