Linking plant nitrogen use efficiency with single traits, ecological strategies and phylogeny in a temperate steppe

Background and aims Nitrogen use efficiency (NUE), defined as plant biomass production per unit N assimilated, is an important component of plant resource use strategies as well as a component of ecosystem function. Clarifying the mechanisms underlying the variations of species level NUE is an essential prerequisite for predicting the alterations of ecosystem level N cycling under global change scenarios. While plant NUE is usually examined under the leaf economic spectrum framework, we know little about their associations with broader ecological strategies and evolutionary history. Methods Using a comparative method, we evaluated the links between NUE and functional traits, Grime’s CSR ecological strategies, and phylogeny for 73 species in a temperate steppe of northern China. Results Plant NUE was strongly constrained by phylogeny, showing a unimodal relationship with taxa divergence times. Under the CSR framework, species with greater R-selection (ruderality) typically had lower NUE. Both phylogeny and R-selection were more important than single functional traits in predicting the species level variations of NUE. Conclusions Our results highlight the role of phylogeny in structuring the species level variations of plant NUE and established a link between species CSR strategies and NUE, which sheds light on understanding the divergence and convergence in plants in response to the most growth-limiting nutrient.