A meta-analysis of mycorrhizal responses to nitrogen, phosphorus, and atmospheric CO2 in field studies


  • Kathleen K. Treseder

    Corresponding author
    1. Department of Ecology and Evolutionary Biology and Department of Earth System Science, University of California, Irvine, CA 92697, USA
    Search for more papers by this author

Author for correspondence: Kathleen K. Treseder Tel: +949-824-7634 Fax: +949-824-2181 Email: Treseder@uci.edu


  • • Numerous field studies have measured mycorrhizal dynamics under additions of nitrogen (N), phosphorus (P), or atmospheric CO2 to test the hypothesis that plants should invest in mycorrhizal fungi when soil nutrients are limiting.
  • • Here meta-analyses were used to integrate nutrient responses across independent field-based studies. Responses were compared between ecto- and arbuscular mycorrhizal fungi, and among fertilizer types, methods of measurement, biomes, and lead investigators. Relationships between degree of response and study length, fertilization rates, total amounts of nutrients applied, and numbers of replicates were also tested.
  • • Across studies, mycorrhizal abundance decreased 15% under N fertilization and 32% under P fertilization. Elevated CO2 elicited a 47% increase. Nitrogen effects varied significantly among studies, and P effects varied significantly among lead investigators. Most other factors did not affect mycorrhizal responses.
  • • These results support the plant investment hypothesis, and suggest that global standing stocks of mycorrhizal fungi may increase substantially under elevated CO2 but decline moderately under P additions. Effects of N deposition may be difficult to predict for individual ecosystems, with a slightly negative influence overall.