Nitrogen limitation of production in a Californian annual grassland: The contribution of arbuscular mycorrhizae

Nutrient availability limits plant production across a wide range of terrestrial ecosystems. In this study of a Californian annual grassland community, the influence of arbuscular mycorrhizal (AM) associations on plant nutrient acquisition was investigated using factorial combinations of nitrogen (N), phosphorus (P) and benomyl fungicide. N additions resulted in a significant increase in shoot biomass demonstrating that plant productivity in these soils was N-limited. The effect of P additions consistently depended on fungicide treatment. In the absence of benomyl, shoot P accumulation was unaltered by P addition. In the presence of benomyl, P addition significantly increased shoot P accumulation and was associated with a consistent trend towards enhanced shoot biomass. The induction of P-deficiency with benomyl application suggests that effective P acquisition by AM may contribute to the strong N-limitation of production observed in many terrestrial ecosystems.