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Updated: May 15, 2026

Understanding Dissolved Organic Matter Biogeochemistry Through In Situ Nutrient Manipulations in Stream Ecosystems
Published on: October 29, 2016
Low biodiversity state persists two decades after cessation of nutrient enrichment
Forest Isbell1, David Tilman, Stephen Polasky
1Department of Ecology, Evolution & Behavior, University of Minnesota Twin Cities, Saint Paul, Minnesota 55108, USA. forest.isbell@gmail.com
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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