PARENT SESSION
Oral Session #40: Biodiversity and Ecosystem Function: Do species and species richness matter?. Presiding: R. Dirzo.
Wednesday, August 8, 2001. 8:00 AM to 12:00 PM. Madison Ballroom D.

Plant species and functional group diversity influence ecosystem responses to elevated CO₂ and nitrogen deposition .

Reich, Peter¹, Tilman, David¹, Craine, Joe², Ellsworth, David³, Knops, Jean⁴, Tjoelker, Mark⁵, Lee, Tali¹, Wedin, David⁴, Naeem, Shahid ⁶, Bahauddin, Dan¹, Goth, Jenny¹, Bengtson, Wendy ¹, ^{1 2 3 4 5 6}

ABSTRACT- Human actions are causing declines in plant biodiversity, increases in atmospheric CO₂ concentrations and increases in nitrogen (N) deposition, but the interactive effects of these factors on ecosystem processes are unknown. To address this issue we are conducting a long-term grassland field experiment in Minnesota, USA that tests the hypothesis that plant diversity and composition influence the enhancement of biomass and carbon (C) acquisition in ecosystems subjected to elevated atmospheric CO₂ concentrations and N deposition. The study experimentally controlled plant diversity (1, 4, 9 or 16 species), soil N (unamended vs. deposition of 4 g N m^-2 yr^-1) and atmospheric CO₂ concentrations using free-air CO₂ enrichment (ambient, 368 vs. elevated, 560 mol mol^-1). From 1998-2000, biomass accumulation was positively affected by all three treatments. However, the enhancement of biomass accumulation in response to elevated levels of CO₂ or N, or their combination, was much less in species-poor than in species-rich assemblages. The biodiversity effects resulted from both sampling effects and positive species interactions. Moreover, subsidiary experiments show that both species richness (holding functional group richness constant) and functional group richness (holding species richness constant) contribute to the diversity effects.

KEY WORDS: Biodiversity, Global Change, Elevated CO₂, Nitrogen Deposition