COS 16-2 - Not just nitrogen and phosphorus: other nutrients also structure a coastal tallgrass prairie plant community

Abstract: Although plants need many essential nutrients, nitrogen and phosphorus have been the major focus of studies seeking to understand plant limitation and community composition. As such, fertilization studies have usually added other nutrients with N and P, obscuring any effects that these other nutrients have individually. We conducted a fertilization study in a coastal tallgrass prairie in Texas in which we added N and P together crossed with separate Ca, K, and Na treatments, for a total of 16 treatments, with each replicated 8 times in large (30x30 m) plots. As many other studies have found, NP fertilization had large effects on plant biomass and taxonomic and functional composition. However, the other elements also affected plant biomass as well as taxonomic and functional plant composition, pointing to a role of Na and Ca in structuring plant communities at this coastal tallgrass prairie site. The effects of Na and Ca often interacted with N&P: Na had positive effects on plant biomass in one year, but the combination of N&P with Na had a suppressing effect on biomass in another year. There was also a small synergistic effect of Ca with N&P with on plant biomass. Responses to these different nutrients were predicted by plant functional traits like plant life form, height, clonality, and stoichiometry. In particular, plants that had high amounts of Ca relative to either N or P responded positively to Ca. At the species level, Na increased the abundance of one sedge, which may be a halophilic species, and Ca increased the abundance of several plants, especially understory species. These results argue for important roles for other elements besides N and P in structuring plant communities, especially Na and Ca at this tallgrass prairie site. Fertilization studies should move beyond a focus on N and P to explicitly test the roles of elements other than N and P in structuring plant communities in other ecosystems.