Community functional traits shift under long-term nitrogen addition: Roles of intraspecific trait variability and species turnover

Abstract Plant functional traits at the community level determine ecosystem responses to environmental change. Despite globally increasing nitrogen deposition, the roles of intraspecific trait variability (ITV) and species turnover in shaping community composition of functional traits under long-term nitrogen deposition remain unclear. We conducted a 10-yr nitrogen addition experiment in an alpine meadow and measured five key leaf traits: leaf nitrogen content (LNC), specific leaf area (SLA), leaf dry matter content (LDMC), leaf thickness (LT), and leaf area (LA). Nitrogen addition increased community-weighted means (CWMs) of LNC and SLA but decreased LT. Sum of squares decomposition revealed that ITV primarily drove changes in LNC, SLA, and LDMC, whereas species turnover mainly influenced LT. ITV was shaped by soil inorganic nitrogen and light availability, while species turnover was mainly driven by soil inorganic nitrogen. These findings reflect the complex adaptive strategies of plant communities in nitrogen-enriched environments and offer insights into the mechanisms driving community composition changes of functional traits under nitrogen addition.