Traits and their plasticity determine responses of plant performance and community functional property to nitrogen enrichment in a boreal peatland

Nitrogen (N) enrichment is well-known to cause declines in plant diversity, yet it remains a challenge to predict which species would be winners or losers. Here, we examined whether traits and their plasticity could predict plant performance under N enrichment, and how changes in plant performance and trait expression could affect community functional property. Relative cover, six leaf traits, and maximum plant height of eight common vascular plants were measured after six-year N addition (0, 3, 6, 12 g N m−2 year−1) in a boreal peatland in Northeast China. Plant performance responding to N enrichment and trait plasticity were separately calculated as changes in relative cover and trait values between control and N addition treatments. Moreover, we quantified relative contributions of species turnover and intraspecific trait variation to changes in functional property. Changes in plant performance were significantly related to plasticity in specific leaf area (SLA) and leaf N concentration (LN) under low N addition, but to maximum plant height under high N addition. When scaled up to the community level, intraspecific trait variation significantly contributed to changes in community-weighted mean leaf area, SLA, leaf tissue density, and LN, and functional diversity of all six leaf traits. These findings highlight the significance of trait plasticity in predicting responses of plant performance and community functional property to N enrichment, and suggest that trait-based approaches are useful in predicting ecological consequences of environmental changes in boreal peatlands.