Role of soil biota in grassland restorations in high nutrient soils

Soil biota are abundant in grasslands; however, disturbances such as invasions or conversion to agriculture may alter soil communities in ways that reduce the success of native species and/or increase the competitiveness of invasive plants. Predicting the magnitude and direction of these effects on plant growth remains challenging, particularly in high nutrient soils, which can impact plant-microbe and plant-plant interactions in different ways. In greenhouse experiments, invasive and native Palouse prairie plants were grown individually and in a community with soil from a Palouse prairie remnant, soil invaded by Bromus tectorum, a nutrient release treatment, or no treatment. We tested (1) whether arbuscular mycorrhizal fungal infectivity and function of soil biota differ in invaded versus remnant prairie soil; (2) if growth responses to soil biota are related to plant nutrient demands; (3) if individual plant responses to soil biota predict competitive outcomes; and (4) if successional status predicts plant growth response to soil biota in high nutrient soils. We found no difference in mycorrhizal inoculation potential or function in invaded versus remnant prairie soil. We show a continuum of plant growth responses to soil biota, which correlate with nutrient responses, even under the high baseline soil nutrient conditions. We found that growth response to soil biota may increase with native plant successional stage. Understanding how different plant species respond to soil biota and assessing functionality of soil biota at a site will help managers plan restorations in high nutrient soils, and inform whether inoculations may be beneficial at a particular site.