The Impacts of Fertilization on Mycorrhizal Production and Investment in Western Gulf Coast Grasslands

—Mycorrhizal fungi are ubiquitous components of terrestrial ecosystems that can influence plant performance, abundance and diversity. Patterns of allocation to specific mycorrhizal fungal structures could provide a useful context for understanding belowground dynamics in response to changing resources. Specifically, increased soil nutrient availability has been predicted to favor plants with lower rates of mycorrhizal association. In addition, fertilization has been predicted to favor mycorrhizae with higher investment in storage structures relative to uptake and exchange structures. A 3 y field experiment was conducted in coastal tallgrass prairie to examine how fertilization affects mycorrhizal abundance and investment patterns. Fertilization significantly increased total mycorrhizal abundance. Specifically, mycorrhizal investment in hyphae, coils and vesicles were significantly increased 53%, 252% and 440% in fertilized plots, respectively. Together these results suggest that mycorrhizae in high fertility soils allocate more to internal fungal storage at a potential cost to plant hosts. Thus, fertilization could have important indirect effects on the aboveground plant community by potentially altering the costs and benefits of mycorrhizae to host plants.