Low biodiversity state persists two decades after cessation of nutrient enrichment

Authors

  • Forest Isbell,

    Corresponding author
    1. Department of Ecology, Evolution & Behavior, University of Minnesota Twin Cities, Saint Paul, Minnesota, USA
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  • David Tilman,

    1. Department of Ecology, Evolution & Behavior, University of Minnesota Twin Cities, Saint Paul, Minnesota, USA
    2. Bren School of the Environment, University of California, Santa Barbara, California, USA
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  • Stephen Polasky,

    1. Department of Ecology, Evolution & Behavior, University of Minnesota Twin Cities, Saint Paul, Minnesota, USA
    2. Department of Applied Economics, University of Minnesota Twin Cities, Saint Paul, Minnesota, USA
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  • Seth Binder,

    1. Department of Ecology, Evolution & Behavior, University of Minnesota Twin Cities, Saint Paul, Minnesota, USA
    2. Department of Applied Economics, University of Minnesota Twin Cities, Saint Paul, Minnesota, USA
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  • Peter Hawthorne

    1. Department of Applied Economics, University of Minnesota Twin Cities, Saint Paul, Minnesota, USA
    2. Institute on the Environment, University of Minnesota Twin Cities, Saint Paul, Minnesota, USA
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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.

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