title: Low biodiversity state persists two decades after cessation of nutrient enrichment.
abstract: Although nutrient enrichment frequently decreases biodiversity, it remains unclear whether such biodiversity losses are readily reversible, or are critical transitions between alternative low- and high-diversity stable states that could be difficult to reverse. Our 30-year grassland experiment shows that plant diversity decreased well below control levels after 10 years of chronic high rates (95-270 kg N ha(-1) year(-1)) of nitrogen addition, and did not recover to control levels 20 years after nitrogen addition ceased. Furthermore, we found a hysteretic response of plant diversity to increases and subsequent decreases in soil nitrate concentrations. Our results suggest that chronic nutrient enrichment created an alternative low-diversity state that persisted despite decreases in soil nitrate after cessation of nitrogen addition, and despite supply of propagules from nearby high-diversity plots. Thus, the regime shifts between alternative stable states that have been reported for some nutrient-enriched aquatic ecosystems may also occur in grasslands.
authors.affiliation: Department of Ecology, Evolution & Behavior, University of Minnesota Twin Cities, Saint Paul, Minnesota 55108, USA. forest.isbell@gmail.com
authors.forename: Forest
authors.initials: F
authors.lastname: Isbell
authors.forename: David
authors.initials: D
authors.lastname: Tilman
authors.forename: Stephen
authors.initials: S
authors.lastname: Polasky
authors.forename: Seth
authors.initials: S
authors.lastname: Binder
authors.forename: Peter
authors.initials: P
authors.lastname: Hawthorne
mesh_terms: D044822:Biodiversity; D018533:Biomass; D017753:Ecosystem; D031749:Elymus; D005308:Fertilizers; D008137:Longitudinal Studies; D009566:Nitrates; D009584:Nitrogen; D010944:Plants; D012987:Soil / Q000737:chemistry*
chemical_list: D005308:Fertilizers; D009566:Nitrates; D012987:Soil; D009584:Nitrogen