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 there are many uncertainties in global change biology, there are also some well documented facts.The amount of carbon dioxide (CO2) in the atmosphere is rising. Since the industrial revolution, the CO2 concentration in the atmosphere has increased from approximately 275 parts per million (ppm) to about 378 ppm today. This has been largely the result of fossil fuel burning. It is expected that CO2 levels will continue to rise, and that by the year 2050 these levels will be approximately 550 ppm. CO2 is the raw material for photosynthesis and is known to affect plant growth and development.
The amount of nitrogen moving through terrestrial ecosystems has increased in the recent past. While natural “background” levels of nitrogen fixation have remained constant, human additions to the system through fertilizer production and fossil fuel use have increased dramatically. Nitrogen is a key nutrient for plant growth and plays a critical role in plant community structure and composition in many environments.
Biodiversity levels are falling. While the research and data are not as complete as they are for CO2 and nitrogen, data indicate that the number of species globally, is being reduced. Perhaps more important for ecosystem function, diversity levels on local to regional scales have fallen due to land use change, biotic invasion and many other drivers.
While much is known about how each of these factors affects ecosystem functioning, many questions remain. There is also little data on how these issues affect each other, and what emergent qualities may arise when systems are exposed to these changes simultaneously. BioCON seeks to address these issues with this multi-year study at Cedar Creek Ecosytem Science Preserve
BioCON is a split-plot arrangement of treatments in a completely randomized design. CO2 treatment is the whole-plot factor and is replicated three times among the six rings. The subplot factors of species nmber and N treatment were assigned randomly and replicated in individual plots among the six rings. For each of the four combinations of CO2 and N levels, pooled across all rings, there were 32 randomly assigned replicates for the plots plant to 1 species (2 replicates per species), 15 for those planted to 4 species, 15 for 9 species, and 12 for 16 species (Reich et al., 2001). This arrangement applies to the “main” experiment which utilizes 296 plots.
There is also a sub experiment within BioCON’s framework in which functional group and species assignments were not completely random; functional group diversity was controlled thereby limiting the choices for species composition. The spatial distribution of plots within the rings was still randomly chosen. See Reich et al., 2004 for a description of design and analysis. The 296 main experiment plots are still utilized in analyses for this part of the study; the species assignments for these plots were necessary to complete the factorial design for functional vs. species diversity analyses. In total there are 371 plots in the BioCON experiment: 296 plots in the main randomly assigned experiment, 63 additional plots for controlling functional group diversity, and 12 bare ground plots, void of any plant species
Beginning in 2007, water treatments were added to 48 of the BioCON 16-species plots.Half of these receive natural rain fall while the other half experience rain removail vie portable rain shelters.The gool of this sub-experiment is to examine how inputs of water, CO2 and N interact to influence soil water availability, soil-plant interactions that influence available N, interactions with the belowground community of decomposers and mutualists, and thus net primary production (NPP) and plant and soil C pools.
1. 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).
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Figure 1. 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. (From Reich et al. 2001.) |
2. At any level of species richness, increasing functional group richness leads to higherbiomass, 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.
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Figure 2. 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. (From Reich et al. PNAS 2004). |
3. 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, unpublished data; 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.
4. Diversity, CO2, and N all influence plant tissue stoichiometry, in particular the C:N ratio (Dijkstra et al. 2005; Reich et al. 2006a; Novotny et al. submitted), which in turn influences the photosynthetic, biomass accumulation, and biogeochemical responses to CO2 and N treatments.
5. Legume N2-fixation increases with elevated CO2 and decreases with increasing soil N, but more so for some species than others (Lee et al. 2003ab, West et al. 2005). The effect of elevated CO2 on Lupinus N2-fixation in mixtures enhances tissue %N and photosynthetic performance of non-fixing neighbors (Lee et al. 2003a, unpublished data).
6. Changes in foliar chemistry caused by CO2, N and competitive gradients (Novotny et al. submitted) influence the incidence and severity of plant disease and insect herbivory (Fig 35; Mitchell et al. 2003, Strengbom and Reich submitted, Strengbom et al. submitted). However, both the nature of the foliar chemical responses and their impacts on disease severity and herbivory are idiosyncratic.
7. Elevated CO2, enriched N, and plant composition and richness influence mycorrhizal and soil decomposer communities (Wolf et al. 2003, Dijkstra et al. 2005, Chung et al. submitted). Additionally, these treatments influence soil C flux, and litter and SOM decomposition, turnover, and mineralization (e.g., Craine et al. 2001bc, Dijkstra et al. 2004, 2005, 2006a; West et al. submitted a), largely reflecting CO2 and N effects on, and species difference in, the chemistry of organic inputs to soils. For example, plant species producing lignin-rich litter increased stabilization of soil C older than 5 years, but only in combination with elevated N inputs (Fig 38), suggesting that N deposition will increase soil C sequestration in those ecosystems where vegetation composition and/or elevated atmospheric CO2 causes high litter lignin inputs to soils.
8. Stoichiometry-dominated relationships between plants, soil microbes and N cycling led to a gradual progressive N limitation of the elevated CO2 fertilization effect (Reich et al. 2006a). This was observed for soil N availability, total plant N pools, and total plant biomass, with soil and plant N dynamics apparently driving the biomass patterns (Fig 6). These results support the idea of N limitation of the CO2 fertilization effect, which has significant implications for the global terrestrial C sink (Hungate et al. 2004).
We propose to continue and expand a wide variety of studies within BioCON that address the five key issues listed above. LTER funds are essential for continuing this research, but it requires substantially more support than LTER can provide. In particular, we will seek to characterize temporal dynamics in plant and ecosystem physiology, community composition, and biotic interactions, including plant-plant interactions, mutualisms, disease, and biogeochemistry, that reflect changes with time in treatment effects on key response variables. Discovering whether there are temporal dynamics to the interactions of plant diversity, CO2 and N and testing hypotheses about the causes and generality of the mechanisms that may drive such interactions are at the core of what makes the BioCON experiment of long-term value.
We will address the role of plant functional (i.e., ecophysiological) diversity in influencing the responses of species in mixtures and monocultures, using a developing plant trait data base in conjunction with the suite of measures mentioned above. We are also using a mechanistic ecosystem model (G’Day, McMurtrie et al. 2000, Corbeels et al. 2005, Pepper et al. 2005) (currently adapted for BioCON as part of ongoing collaboration with R. McMurtrie and B. Medlyn) to assess whether trait-driven differences in photosynthesis, canopy dynamics, and biogeochemistry lead to predicted biomass accumulation patterns that match the observed timebcourse of the progressive N limitation of CO2 fertilization as it continues to unfold over time.
Adair, E. C., P. B. Reich,* S. E. Hobbie*, and J. M. H. Knops. In press. Interactive effects of time, CO2, N and diversity on total belowground carbon allocation and ecosystem carbon storage in a grassland community. Ecosystems 2009 e141
Antonika, A.; Wolf, J.; Bowker, M.; Classen, A. T.; Johnson, N. C.; Linking above- and belowground responses to global change at community and ecosystem scales. Global Change Biology 15:914-929, 2009 2009 [Abstract] [Full Text] e141
Bassirirad, H.; Constable, J. V. H.; Lussenhop, J.; Kimball, B. A.; Norby, R. J.; Oechel, W. C.; Reich, P. B.; Schlesinger, W. H.; Zitzer, S.; Sehtiya, H. L.; Salim, S.; Widespread foliage 15N depletion under elevated CO2: inferences for the nitrogen cycle. Global Change Biology 9:1-9. 2003 [Full Text] e141
Craine, J. M.; Reich, P. B.; Elevated CO2 and nitrogen supply alter leaf longevity of grassland species. New Phytologist 150:397-403. 2001 [Full Text] e141
Craine, J. M.; Reich, P. B.; Tilman, D.; Ellsworth, D.; Fargione, J.; Knops, J.; Naeem, S.; The role of plant species in biomass production and response to elevated CO2 and N. Ecology Letters 6:623-630. 2003 [Full Text] e141
Craine, J. M.; Wedin, D. A.; Reich, P. B.; Grassland species effects on soil CO2 flux track the effects of elevated CO2 and nitrogen. New Phytologist 150:425-434. 2001 [Full Text] e141
Dijkstra, F. A.; Hobbie, S. E.; Knops, J. M. H.; Reich, P. B.; Nitrogen deposition and plant species interact to influence soil carbon stabilization. Ecology Letters 7:1192-1198. 2004 [Full Text] e141
Dijkstra, F. A.; Hobbie, S. E.; Reich, P. B.; Knops, J. M. H.; "Divergent effects of elevated CO2, N fertilization, and plant diversity on soil C and N dynamics in a grassland field experiment. Plant and Soil 272:41-52." 2005 [Full Text] e141
Dijkstra, F. A.; Hobbie, S. E.; Reich, P. B.; Soil processes affected by sixteen grassland species grown under different environmental conditions. Soil Science Society of America Journal 70:770-777. 2005 [Abstract] [Full Text] e141
Dijkstra, F.A.; West, J.B.; Hobbie, S.E.; Reich, P.B.; Trost, J.; Plant diversity, CO2, and N influence inorganic and organic n leaching in grasslands. ECOLOGY 88:490-500. 2007 [Abstract] [Full Text] e141
Ellsworth, D. S.; Reich, P. B.; Naumburg, E. S.; Koch, G. W.; Kubiske, M.; Smith, S.; "Photosynthesis, carboxylation and leaf nitrogen responses of 16 species to elevated pCO2 across four free-air CO2 enrichment experiments in forest, grassland and desert. Global Change Biology 10:2121-2138." 2004 [Full Text] e141
HilleRisLambers, J., W.S. Harpole, S. Schnitzer, D. Tilman and P.B. Reich, "CO2, nitrogen and diversity differentially affect seed production of prairie grasses", Ecology, p. , vol. Accepted 2008 e141
Knops, J.M.H.; Koenig, W.D.; Carmen, W.J.; Negative correlation does not imply a tradeoff between growth and reproduction in California oaks. PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 104:16982-16985. 2007 [Abstract] [Full Text] e141
Lau, J. A.; Tiffin, P.; Elevated carbon dioxide concentrations indirectly affect plant fitness by altering plant tolerance to herbivory. Oecologia 161:401-410. 2009 [Abstract] [Full Text] e141
Lau, J.; Shaw, R.; Reich, P.; Tiffin, P.; Elevated atmospheric CO2 has little effect on the evolution of ecologically important traits in Arabidopsis thaliana. New Phytologist. 2007 e141
Lau, J.; Strengbom, J.; Stone, L.; Reich, P.; Tiffin, P.; Global environmental changes alter plant-enemy interactions via effects on plant traits. Ecology. 2007 e141
Lee, T. D.; Reich, P. B.; Tjoelker, M. G.; Legume presence increases photosynthesis and N concentrations of co-occurring non-fixers but does not modulate their responsiveness to carbon dioxide enrichment. Oecologia 137:22-31. 2003 [Full Text] e141
Lee, T. D.; Tjoelker, M. G.; Ellsworth, D. S.; Reich, P. B.; Leaf gas exchange responses of 13 prairie grassland species to elevated CO2 and increased nitrogen supply. New Phytologist 150(2):405-418. 2001 [Full Text] e141
Mitchell, C.; Reich, P. B.; Assessing environmental changes in grasslands. Science 299:1844 2003 [Full Text] e141
Mitchell, C.; Reich, P. B.; Tilman, D.; Groth, J. V.; "Effects of elevated CO2, nitrogen deposition, and decreased species diversity on foliar fungal plant disease. Global Change Biology 9:438-451" 2003 [Full Text] e141
Naeem, S.; Disentangling the impacts of functional and taxonomic diversity on ecosystem functioning in synthetic-community experiments. Ecology 83:2925-2935. 2002 [Full Text] e141
Reich, P.; Hobbie, S.E.; Lee, T.; Ellsworth, D.S.; West, J.B.; Tilman, D.; Knops, J.M.H.; Naeem, S.; Trost, J.; Nitrogen limitation constrains sustainability of ecosystem response to CO2. NATURE 440:922-925. 2006 [Abstract] [Full Text] e141
Reich, P.; Knops, J.; Tilman, D.; Craine, J.; Ellsworth, D.; Tjoelker, M.; Lee, T.; Wedin, D.; Naeem, S.; Bahauddin, D.; Hendrey, G.; Jose, S.; Wrage, K.; Goth, J.; Bengston, W.; Plant diversity enhances ecosystem responses to elevated CO2 and nitrogen deposition. Nature 410:809-812. 2001 [Full Text] e141
Reich, P.; Knops, J.; Tilman, D.; Craine, J.; Ellsworth, D.; Tjoelker, M.; Lee, T.; Wedin, D.; Naeem, S.; Bahauddin, D.; Hendrey, G.; Jose, S.; Wrage, K.; Goth, J.; Bengston, W.; Plant diversity enhances ecosystem responses to elevated CO2 and nitrogen deposition. Nature 410:809-812. 2001 [Full Text] e141
Reich, P.; Tilman, D.; Craine, J.; Ellsworth, D.; Tjoelker, M. G.; Knops, J.; Wedin, D.; Naeem, S.; Bahauddin, D.; Goth, J.; Bengtson, W.; Lee, T. D.; "Do species and functional groups differ in acquisition and use of C, N and water under varying atmospheric CO2 and N availability regimes? A field test with 16 grassland species. New Phytologist 150:435-448." 2001 [Full Text] e141
Reich, P.; Tilman, D.; Naeem, S.; Ellsworth, D.; Knops, J.; Craine, J.; Wedin, D.; Trost, J.; Species and functional group diversity independently influence biomass accumulation and its response to CO2 and N. Proceedings of the National Academy of Sciences 101:10101-10106 ?? 2004 [Full Text] e141
West, J.; Hobbie, S.E.; Reich, P.B.; "Effects of plant species diversity, atmospheric [CO2], and N addition on gross rates of inorganic N release from soil organic matter. GLOBAL CHANGE BIOLOGY 12:1400-1408." 2006 [Abstract] [Full Text] e141
Wolf, J.; Johnson, N. C.; Rowland, D. L.; Reich, P. B.; Elevated CO2 and plant species richness impact arbuscular mycorrhizal fungal spore communities. New Phytologist 157:579-588. 2003 [Full Text] e141
