Interactive effects of nutrient deposition and soil biota on plant competition

Arbuscular mycorrhizal (AM) fungi increase plant access to phosphorus in exchange for sugars from photosynthesis and can provide a competitive advantage in low nutrient soils. Increased phosphorus deposition may change AM fungal community composition, which in turn can influence competitive interactions among plant species. The aim of this study was to examine how phosphorus fertilizer and soil biota influence fungal effects on plant growth and competitive interactions between species that have strong (Andropogon gerardii) and weak (Bromus inermis) responses to AM fungi. The AM fungal community at sites with differences in soil fertilization can slightly influence the outcome of competition under low phosphorus fertilizer, however A. gerardii was strongly limited by its non-native competitor under high phosphorus fertilizer. My study suggests that invasive grass species may have a competitive advantage over low nutrient-adapted native species, even when native species receive greater benefits from mutualistic fungi.