Sodium co‐limits and catalyzes macronutrients in a prairie food web

Abstract

Abstract Nitrogen and phosphorus frequently limit terrestrial plant production, but have a mixed record in regulating the abundance of terrestrial invertebrates. We contrasted four ways that Na could interact with anNPfertilizer to shape the plants and invertebrates of an inland prairie. We appliedNPand Na to m2plots in a factorial design. Aboveground invertebrate abundance was independently co‐limited by NaCl andNP, but with +NPplots supporting more individuals. We suggest the disparity arises becauseNPenhanced plant height by 35% (1 SD) over controls, providing both food and habitat, whereas NaCl provides only food. Belowground invertebrates showed evidence of serial co‐limitation, where NaCl additions alone were ineffectual, but catalyzed access toNP. This suggests the increased belowground food availability inNPplots increased Na demand. Na andNPsupply rates vary with climate, land use, and with inputs like urine. The co‐limitation and catalysis of N and P by Na thus has the potential for predicting patterns of abundance and diversity across spatial scales.