Aims Human activities have dramatically increased nutrient inputs to ecosystems, impacting plant community diversity, composition and functioning. Extensive research has shown that a decrease in species diversity and an increase in productivity are a common phenomenon following fertilization in grasslands ecosystem. The magnitude of the response of species diversity and above-ground net primary productivity (ANPP) to fertilization mainly depends on species traits (mean trait values) and traits variability (plasticity). Our aim of this study was to examine (i) changes of species diversity (species richness and Shannon–Wiener index) and ANPP following fertilization; (ii) which species traits or community-weighted mean (CWM) traits can determine ANPP, as expected from the 'biomass ratio hypothesis'; and (iii) the relative role of intra-specific and inter-specific trait variability in this process following fertilization.
Methods We measured ANPP and four key plant functional traits: specific leaf area (SLA), leaf dry matter content (LDMC), mature plant height (MPH) and leaf nitrogen concentration (LNC) for 25 component species along a fertilization gradient in an alpine meadow on the Tibetan Plateau. In addition, trait variation of species was assessed using coefficients of variation (CV), and we calculated the ratio of the CV intra to the CV inter.
Important findings Our results showed that: (i) fertilization significantly reduced species richness and Shannon–Weiner diversity index, but significantly increased ANPP; (ii) there was a significant positive correlation between ANPP and CWM–SLA and CWM–MPH, yet there was no significant relationship between ANPP and CWM–LNC or CWM–LDMC; (iii) intra-specific variability in SLA and MPH was found to be much greater than inter-specific variability, especially at the higher fertilization levels. We concluded that CWM–SLA and CWM–MPH can be used to assess the impacts of species changes on ecosystem functioning, and dominant species can maximize resource use through intra-specific variability in SLA and MPH to compensate for the loss of species following fertilization, therefore maintaining high community productivity.