Plant community controls on short-term ecosystem nitrogen retention

Retention of nitrogen (N) is a critical ecosystem function, especially in the face of widespread anthropogenic N enrichment; however, our understanding of the mechanisms involved is limited. Here, we tested under glasshouse conditions how plant community attributes, including variations in the dominance, diversity and range of plant functional traits, influence N uptake and retention in temperate grassland. We added a pulse of 15N to grassland plant communities assembled to represent a range of community-weighted mean plant traits, trait functional diversity and divergence, and species richness, and measured plant and microbial uptake of 15N, and leaching losses of 15N, as a short-term test of N retention in the plant–soil system. Root biomass, herb abundance and dominant plant traits were the main determinants of N retention in the plant–soil system: greater root biomass and herb abundance, and lower root tissue density, increased plant 15N uptake, while higher specific leaf area and root tissue density increased microbial 15N uptake. Our results provide novel, mechanistic insight into the short-term fate of N in the plant–soil system, and show that dominant plant traits, rather than trait functional diversity, control the fate of added N in the plant–soil system.