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Keywords:

  • climate change;
  • freezing;
  • grasses;
  • nitrogen (N) deposition;
  • plant productivity;
  • snow removal

Summary

  • Plant responses to increased atmospheric nitrogen (N) deposition must be considered in the context of a rapidly changing climate. Reductions in snow cover with climate warming can increase the exposure of herbaceous plants to freezing, but it is unclear how freezing damage may interact with increased N availability, and to what extent freezing effects may extend over multiple years.
  • We explored potential interactions between freezing damage and N availability in the context of plant productivity and relative species abundance in a temperate old field using both snow removal and mesocosm experiments, and assessed the legacy effects of the freezing damage over 3 yr.
  • As expected, N addition increased productivity and freezing damage decreased productivity, but these factors were nonadditive; N addition increased productivity disproportionately in the snow removal plots, whereas extreme freezing diminished N addition responses in the mesocosm experiment. Freezing altered relative species abundances, although only the most severe freezing treatments exhibited legacy effects on total productivity over multiple growing seasons.

  • Our results emphasize that while both increased N deposition and freezing damage can have multi-year effects on herbaceous communities, the interactions between these global change factors are contingent on the intensities of the treatments.