Nitrate leaching as a function of plant community richness and composition,and the scaling of soil nutrients,in a restored temperate grassland

Two, two-factor experiments manipulated species and functional form plant richness and the spatial scaling of either nitrogen (N) or phosphorous (P) in restored tallgrass prairie in North Dakota, USA. Nitrate (NO₃ ⁻) leaching was measured in these plots and analyzed for its response to the treatment factors and measured plant community parameters. Nitrate extracted from anion exchange resin was regressed against the first principal component of species and functional form richness, the spatial scaling of N or P, the measured biomass of the functional forms used and the plot values for plant parameters based on weighted averages by species biomass. The treatments applied in the N and P experiments were 1, 2, 5, 10, or 20 plant species taxa, and the application of fertilizer in a random fractal pattern with either fine-scale or coarse-scale heterogeneity. Nitrate leaching decreased with plant diversity and increased by a factor of two going from fine-scale to coarse-scale N. It was also related to a number of plant functional parameters, and was positively correlated with the biomass of late successional C₃ grasses (Koeleria cristata (Lam.) Beauv., Poa pratensis L., Stipa comata Trin. & Rupr., and Stipa viridula Trin.), which are known from previous studies to have negative mycorrhizal responsiveness and are characterized by high root lateral spread per unit of root biomass. Our results show that while plant diversity has a highly significant influence on plant community uptake of NO₃ ⁻, this effect is mediated by the scaling of soil N and the functional traits of the species comprising the plant assemblage.