Locally adapted arbuscular mycorrhizal fungi improve vigor and resistance to herbivory of native prairie plant species

Soil microbial communities contribute to ecosystem function and structure plant communities, but are altered by anthropogenic disturbance. Successful restoration may require microbial community restoration. Inoculation of plants with arbuscular mycorrhizal fungi (AMF) may improve ecological restoration, but AMF species that are locally adapted to native plant communities are often unavailable and commercially propagated AMF are not necessarily locally adapted to the desired plant community target. The disconnect between readily available commercial fungi and later-successional plants may inhibit successful establishment of the restoration. We tested this concept using four mid-to late successional prairie plant species planted with one of three inoculum sources: a locally adapted AMF mix cultured from native prairie, a non-locally adapted commercial AMF product, or a sterilized background soil control. The inoculated plants (termed nurse plants) were planted in the middle of field plots. In each plot, uninoculated plants (test plants) were planted at 0.5, 1, and 2 m from the nurse plants in order to test whether growth and survival of test plants could be affected by inoculum source. Generally, plants grew larger when inoculated with native AMF compared to commercial inoculum or the control. Later successional species responded most positively to native AMF. Benefits of inoculation also spread to neighbors, as uninoculated late successional test plant, Sporobolus heterolepis, grew larger when its' neighbors were inoculated with native AMF than with commercial AMF or the control. Due to an unanticipated herbivory event, we also assessed the degree to which rate of herbivory or plant tolerance to herbivory is affected by inoculum source. The mid-successional nurse plant, Ratibida pinnata, received the majority of the herbivore damage, and when it was inoculated with commercial AMF, it experienced significantly more herbivory than plants inoculated with native AMF or the control. R. pinnata inoculated with native AMF grew significantly larger one month following herbivory, though there was no significant difference in growth in the second year of sampling. This study suggests that native, locally adapted AMF can improve restoration of prairie plant species and these benefits can extend to neighbors up to two meters from the inoculation point.