Increased rainfall and nitrogen alter colonization and extinction during postgrazing steppe succession

Abstract

AbstractQuestionSteppes may be sensitive to rainfall and nitrogen (N) pulses; however, their potential effects on local colonization and extinction during postgrazing steppe succession have not been thoroughly elucidated to date. We addressed how increased rainfall and N influenced plant species richness, gain, loss, and turnover in an ungrazed steppe.LocationNortheastern Inner Mongolia, China.MethodsWe performed a five‐growing‐season field experiment, in which an ungrazed steppe was subject to nine different combinations of rainfall and N. The three rainfall levels were ambient amount of rainfall, a 14% increase in amount of rainfall, and a 28% increase in amount of rainfall; the three N levels were no N addition, an addition of 5 g N m−2 year−1, and an addition of 10 g N m−2 year−1. We determined successional changes at the taxonomic and functional levels by surveying plant species in the first and fifth growing seasons.Results(a) Increased rainfall and N addition did not affect plant species richness but did influence plant species loss, gain, and turnover. (b) At the taxonomic level, species loss, gain, and turnover decreased monotonically with increasing rainfall; N addition decreased species loss and turnover but did not influence species gain; the slope of the species loss–gain relation was approximately 1.0. (c) At the plant functional group level, increased rainfall favored C3 plants by sustaining species gain and decreasing species loss; N addition favored C4 plants by increasing the species gain and decreasing the species loss.ConclusionIncreased rainfall and simulated N deposition could induce rapid colonization and extinction during postgrazing steppe succession, but maintain plant diversity homeostasis by equally affecting species colonization and extinction. Future rainfall enrichment and N deposition might strongly influence the relative abundance of different plant functional groups, thereby affecting successional changes under global change.