Tradeoffs and thresholds in the effects of nitrogen addition on biodiversity and ecosystem functioning: Evidence from inner Mongolia Grasslands

Yongfei Bai, Jianguo Wu, Christopher M. Clark, Shahid Naeemz, Qingmin Pan, Jianhui Huang, Lixiaz Hang, Xingguo Han

Research output: Contribution to journalArticle

408 Scopus citations

Abstract

Nitrogen (N) deposition is widely considered an environmental problem that leads to biodiversity loss and reduced ecosystem resilience; but, N fertilization has also been used as a management tool for enhancing primary production and ground cover, thereby promoting the restoration of degraded lands. However, empirical evaluation of these contrasting impacts is lacking.We tested the dual effects of N enrichment on biodiversity and ecosystem functioning at different organizational levels (i.e., plant species, functional groups, and community) by adding N at 0, 1.75, 5.25, 10.5, 17.5, and 28.0 gNm-2 yr-1 for four years in two contrasting field sites in Inner Mongolia: an undisturbed mature grassland and a nearby degraded grassland of the same type. N addition had both quantitatively and qualitatively different effects on the two communities. In the mature community, N addition led to a large reduction in species richness, accompanied by increased dominance of early successional annuals and loss of perennial grasses and forbs at all N input rates. In the degraded community, however, N addition increased the productivity and dominance of perennial rhizomatous grasses, with only a slight reduction in species richness and no significant change in annual abundance. The mature grassland was much more sensitive to N-induced changes in community structure, likely as a result of higher soil moisture accentuating limitation by N alone. Our findings suggest that the critical threshold for N-induced species loss to mature Eurasian grasslands is below 1.75 gNm-2 yr-1, and that changes in aboveground biomass, species richness, and plant functional group composition to both mature and degraded ecosystems saturate at N addition rates of approximately 10.5 gNm-2 yr-1. This work highlights the tradeoffs that exist in assessing the total impact of N deposition on ecosystem function.

Original languageEnglish (US)
Pages (from-to)358-372
Number of pages15
JournalGlobal Change Biology
Volume16
Issue number1
DOIs
StatePublished - Jan 1 2010

Keywords

  • Aboveground biomass
  • Ecological restoration
  • Ecosystem management
  • Eurasia steppe
  • Nitrogen enrichment
  • Plant functional group composition
  • Species richness

ASJC Scopus subject areas

  • Global and Planetary Change
  • Environmental Chemistry
  • Ecology
  • Environmental Science(all)

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