Using arbuscular mycorrhizae in prairie restoration: Sources, methods, and short-term successes

Background/Question/Methods

Today, native grasslands are one of the most threatened ecosystems in the United States. Native prairie habitats have been nearly extirpated from the Pacific Northwest and are the most endangered ecosystem in Washington State. Past efforts to restore these landscapes have focused primarily on outplanting containerized seedlings of native plant species important for rare butterflies, an extremely labor- and resource-intensive approach. Long-term survivorship of these plants has been low (20-50%), suggesting that the nursery-raised plants are not well-adapted for harsh prairie conditions (summer drought and low soil nutrients). Mycorrhizal fungi may help to increase drought resistance and nutrient acquisition for outplanted seedlings. In an attempt to determine effectiveness of mycorrhizal inoculation on establishment of nursery-grown plants, we outplanted seedlings of four prairie species at three different restored prairie sites that were either inoculated with a ‘native’ mycorrhizal mix or un-inoculated. The ‘native’ mycorrhizal mix was cultivated from roots of eight different prairie species. First year seedlings were monitored for survivability, vigor (plant height) and reproductive capacity (number of flowering heads).

Results/Conclusions

First year survivorship data for most species showed site to be more significant than mycorrhizal treatment, suggesting that other abiotic or biotic variables present at the sites control initial establishment. However, the response of plant vigor and reproductive capacity to mycorrhizal treatment varied by species. Mycorrhizal inoculation increased the vigor of two of the plant species and it increased reproductive capacity of only one of the four species. These short-term data suggest that mycorrhizal inoculation can be either beneficial or detrimental to rare prairie plants, so caution should be used when applying this restoration method across a suite of species. Additionally, the type of inoculum used may influence the treatment effectiveness.