Soil management strategies can have negative impacts on soil microbial communities. In high-nutrient soils, arbuscular mycorrhizal fungi can parasitize their hosts rather than acting as mutualistic partners. This greenhouse study uses switchgrass (Panicum virgatum L.), a C4 grass, to compare the benefits of mycorrhizae derived from nitrogen-fertilized fields or legume-interplanted fields in NE Wisconsin for the host plant. Plant growth, percent root length colonized, and phosphorus uptake were compared among three soil treatments from each field management regime: living soil unaltered from the field, sterilized soil with non-fungi microbes added back in, and sterilized soil. As predicted, the plants with the live soil from legume-interplanted fields benefitted most from mycorrhizae in terms of growth. Phosphorus content analyses are ongoing, but we expect plants with more beneficial mycorrhizae will have access to increased phosphorus. These results suggest switchgrass, and other C4 crops, ordinarily gain growth advantages from mycorrhizae and non-fungi microbes, but this mutualism can be disrupted by nitrogen fertilizer.
