Legumes regulate grassland soil N cycling and its response to variation in species diversity and N supply but not CO2

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Legumes are an important component of plant diversity that modulate nitrogen (N) cycling in many terrestrial ecosystems. Limited knowledge of legume effects on soil N cycling and its response to global change factors and plant diversity hinders a general understanding of whether and how legumes broadly regulate the response of soil N availability to those factors. In a 17-year study of perennial grassland species grown under ambient and elevated (+180 ppm) CO2 and ambient and enriched (+4 g N m−2 year−1) N environments, we compared pure legume plots with plots dominated by or including other herbaceous functional groups (and containing one or four species) to assess the effect of legumes on N cycling (net N mineralization rate and inorganic N pools). We also examined the effects of numbers of legume species (from zero to four) in four-species mixed plots on soil N cycling. We hypothesized that legumes would increase N mineralization rates most in those treatments with the greatest diversity and the greatest relative limitation by and competition for N. Results partially supported these hypotheses. Plots with greater dominance by legumes had greater soil nitrate concentrations and mineralization rates. Higher species richness significantly increased the impact of legumes on soil N metrics, with 349% and 505% higher mineralization rates and nitrate concentrations in four-species plots containing legumes compared to legume-free four-species plots, in contrast to 185% and 129% greater values, respectively, in pure legume than nonlegume monoculture plots. N-fertilized plots had greater legume effects on soil nitrate, but lower legume effects on net N mineralization. In contrast, neither elevated CO2 nor its interaction with legumes affected net N mineralization. These results indicate that legumes markedly influence the response of soil N cycling to some, but not all, global change drivers.

Original languageEnglish (US)
Pages (from-to)2396-2409
Number of pages14
JournalGlobal change biology
Issue number7
StatePublished - Jul 2019

Bibliographical note

Funding Information:
This study was funded by programs from the U.S. National Science Foundation (NSF) Long-Term Ecological Research (DEB-9411972, DEB-0080382, DEB-0620652, and DEB-1234162), Biocomplexity Coupled Biogeochemical Cycles (DEB-0322057), Long-Term Research in Environmental Biology (DEB-0716587, DEB-1242531), Ecosystem Sciences (NSF DEB-1120064) Programs, the U.S. Department of Energy Programs for Ecosystem Research (DE-FG02-96ER62291), and the National Institute for Climatic Change Research (DE-FC02-06ER64158). Kally Worm and Dan Bahauddin assisted with data collection and management.

Publisher Copyright:
© 2019 John Wiley & Sons Ltd


  • CO elevation
  • N enrichment
  • net N mineralization
  • numbers of legume species
  • soil inorganic N
  • species richness


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