Enriched Atmosphere

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Change in total (above-ground plus 0±20 cm belowground) biomass (compared with ambient levels of both CO2 and N) in response to elevated CO2 alone (at ambient soil N), to enriched N alone (at ambient CO2), and to the combination of elevated CO and enriched soil N, for plots containing 1, 4, 9 or 16 species. Data were averaged for 4 harvests over 2 yr. Per cent change is shown above each histogram for each diversity treatment.
Reich et al. 2001

Cedar Creek research demonstrates that anticipated atmospheric CO2 levels predicted for 2075 will increase plant growth and carbon sequestration in grasslands in fertile areas, but only weakly in arid ecosystems with low nitrogen. These results suggest that ultimately atmospheric CO2 levels will rise faster than predicted by leading models.

BioCON (Biodiversity, CO2, and Nitrogen) is an experiment started in 1997 with the goal of exploring the ways in which plant communities will respond to three environmental changes that are known to be occurring on a global scale: increasing nitrogen deposition, increasing atmospheric CO2, and decreasing biodiversity. While much is known about how each of these factors affects ecosystem functioning, many questions remain. There had been little data on how these issues affect each other, and what emergent qualities may arise when systems are exposed to these changes simultaneously. BioCON is addressing these issues with this multi-year study at Cedar Creek Ecosytem Science Preserve

Researchers at Cedar Creek have found that low species diversity constrained plant biomass accumulation in response to CO or N or their combination (Fig 1; Reich et al. 2001). Additionally, in a complementary experiment we found the impacts of diversity on biomass, and on the biomass response to CO2 and N, are independently caused by both species and functional group richness (Reich et al. 2004). At any level of species richness, increasing functional group richness leads to higher biomass, while at any level of functional group richness, increasing species richness leads to higher biomass (Fig 2). The effects of increasing species richness within functional groups occurred in all functional groups, and as well, the effects of increasing functional group richness were seen in all functional group combinations. Species and functional groups differ in long-term acclimation (i.e., down-regulation) of photosynthesis to variable CO2 and N supply (Lee et al. 2001; Ellsworth et al. 2004), with a direct stoichiometric feedback of CO2 on tissue N leading to lower potential photosynthetic capacity at any given CO2 concentration.

Effects of S at a standardized F on biomass and biomass responses to elevated CO2 and enriched N. (A) In experiment I, total biomass (above-ground plus below-ground, 0– 20 cm in depth; +1 SE) for plots planted with one functional group (F = 1) and either one or four species, grown at four combinations of ambient (368 μmol•mol-1) and elevated (560 μmol•mol-1) concentrations of CO2 and ambient N and enriched N (4 g•m-2•year-1). Data were averaged over two harvests in each year from 1998 to 2001. (B) In experiment I, the change in total biomass (compared with ambient levels of both CO2 and N) in response to elevated CO2 alone (at ambient N), to enriched N alone (at ambient CO2), and to the combination of elevated CO2 and enriched N, pooled across years, for plots with F = 1 and S = 1 or 4. Effects of F at a standardized S on biomass and biomass responses to elevated CO2 and enriched N. All data were from experiment III. (C) Total biomass (aboveground plus below-ground, 0–20 cm in depth; +1 SE) for plots planted with four species (S = 4) drawn from 1, 2, 3, or 4 functional groups, grown at four combinations of ambient (368 μmol•mol-1) and elevated (560 μmol•mol-1) concentrations of CO2 and ambient N and enriched N (4 g•m-2•year-1). Data were averaged over two harvests in each year from 1998 to 2001. (D) Change in total biomass (compared with ambient levels of both CO2 and N) in response to elevated CO2 alone (at ambient N), to enriched N alone (at ambient CO2), and to the combination of elevated CO2 and enriched N, in each year, for plots with S=4 and F=1, 2, 3, or 4.
Reich et al. PNAS 2004
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