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Cedar Creek Ecosystem Science Reserve

Cedar Creek Ecosystem Science Reserve

BioCON: Biodiversity, CO2, and Nitrogen

Experiment 141 Data

Introduction

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 Ecosystem 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 9-species plots. Half of these receive natural rain fall while the other half experience rain removal via portable rain shelters. The goal 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.

Key Results

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).


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 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.


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).

Future Research

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 time because of the progressive N limitation of CO2 fertilization as it continues to unfold over time.

Associated Publications

Adair, Carol; Reich, Peter; Trost, Jared; Hobbie, Sarah; Elevated CO2 stimulates grassland soil respiration by increasing carbon inputs rather than by enhancing soil moisture. 2011. Global Change Biology 17:3546 2011 [Full Text] e141

Adair, E. C.; Reich, P. B.; Hobbie, S. E.; Knops, J. M. H.; Interactive effects of time, CO2, N and diversity on total belowground carbon allocation and ecosystem carbon storage in a grassland community. Ecosystems 12:1037 2009 [Full Text] e141

Ali, Ashehad A.; Medlyn, Belinda E.; Crous, Kristine Y.; Reich, Peter B.; A trait-based ecosystem model suggests that long-term responsiveness to rising atmospheric CO2 concentration is greater in slow-growing than fast-growing plants Functional Ecology 2013, 27, 10111022; doi: 10.1111/1365-2435.12102 2013 [Full Text] 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

Antoninka, Anita; Reich, Peter B.; Johnson, Nancy Collins; Seven years of carbon dioxide enrichment, nitrogen fertilization and plant diversity influence arbuscular mycorrhizal fungi in a grassland ecosystem. New Phytologist 192:200. 2011 [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

Brzostek, Edward R.; Blair, John M.; Dukes, Jeffrey S.; Frey, Serita D.; Hobbie, Sarah E.; Melillo, Jerry M.; Mitchell, Robert J.; Pendall, Elise; Reich, Peter B.; Shaver, Gaius R.; Stefanski, Artur; Tjoelker, Mark G.; Finzi, Adrien C.; The effect of experimental warming and precipitation change on proteolytic enzyme activity: positive feedbacks to nitrogen availability are not universal; Global Change Biol.; 2012; 18, 8, 2617-2625 2012 [Full Text] e141

Chung, H. L.; Reich, P. B.; Ellsworth, D.; "Plant species richness, elevated CO2, and atmospheric N deposition alter soil microbial community composition and function. Global Change Biology 13:980-989" 2007 [Abstract] [Full Text] e141

Clark,C. M., Flynn, D. F. B., Butterfield, B. J.; Reich, P. B.; (2012); Testing the Link between Functional Diversity and Ecosystem Functioning in a Minnesota Grassland Experiment.; PLoS ONE 7(12): e52821.; doi:10.1371/journal.pone.0052821 2012 [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.; Determinants of growing season soil CO2 flux in a Minnesota grassland. Biogeochemistry 59:303-313. 2002 [Full Text] e141

Craine, J. M.; Wedin, D. A.; Reich, P. B.; "The response of soil CO2 flux to changes in atmospheric CO2, nitrogen supply and plant diversity. Global Change Biology 7:947-953." 2001 [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

Crous, K; Reich, Peter; Hunter, M; Ellsworth, D; Maintenance of leaf N controls the photosynthetic CO2 response of grassland species exposed to 9 years of free-air CO2 enrichment. 2010. Global Change Biology 16:2076 2010 [Full Text] e141

Danz, Nicholas P.; Frelich, Lee E.; Reich, Peter B.; Niemi, Gerald J.; Do vegetation boundaries display smooth or abrupt spatial transitions along environmental gradients? Evidence from the prairie-forest biome boundary of historic Minnesota, USA; Journal of Vegetation Science; 2013; 24, 6, 1129-1140; Doi: 10.1111/jvs.12028 2013 [Full Text] e141

Davis, M.; Reich, P. B.; Knoll, J.; Dooley, L.; Hundtoft, M.; Attleson, I.; Elevated atmospheric C02: a nurse plant substitute for oak seedlingsestablishing in old fields. Global Change Biology 13:2308-2316. 2007 [Abstract] [Full Text] e141

De Graaff, Marie-Anne; Van Groenigen, Kees-Jan; Six, Johan; Hungate, Bruce; Van Kessel, Chris; Interactions between plant growth and soil nutrient cycling under elevated CO2: a meta-analysis. Global Change Biology. 12:20772091 2006 [Full Text] e141

Deng, Y.; He, Z.; Xu, M.; Qin, Y.; Van Nostrand, J. D.; Wu, L.; Roe, B. A.; Wiley, G.; Hobbie, S. E.; Reich, P. B.; Zhou, J.; Elevated carbon dioxide alters the structure of soil microbial communities.; Appl Environ Microbiol. 78(8):2991-2995. 2012 [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. 2006 [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

Eisenhauer, N., Dobies, T.; Cesarz, S.; Hobbie, S. E.; Meyer, R. J.; Worm, K.; Reich. P. B.; 2013; Plant diversity effects on soil food webs are stronger than those of elevated CO2 and N deposition in a long-term grassland experiment.; PNAS 110:6889-6894 2013 [Full Text] e141

Eisenhauer, Nico; Cesarz, Simone; Koller, Robert; Worm, Kally; Reich, Peter B.; Global change belowground: impacts of elevated CO2, nitrogen, and summer drought on soil food webs and biodiversity. Global Change Biology. 18:435447, doi: 10.1111/j.1365-2486.2011.02555.x 2012 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

He, Z; Xu, M; Deng, Y; Kang, S; Kellogg, L; Wu, L; J, Van Nostrand; Hobbie, Sarah; Reich, Peter; Zhou, J; Metagenomic analysis reveals a marked divergence in the structure of belowground microbial communities at elevated CO2. 2010. Ecology letters 13:564 2010 [Full Text] e141

Hillerislambers, J.; Harpole, W. S.; Schnitzer, S.; Tilman, D.; Reich, P. B.; CO2, nitrogen, and diversity differentially affect seed production of prairie plants. Ecology. 90:18101820 2009 [Full Text] 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

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

Lee, T.; Barrott, S.; Reich, P.; Photosynthetic responses of 13 grassland species across 11 years of free-air CO2 enrichment is modest, consistent and independent of N supply. 2011. Global Change Biology 17:2893 2011 [Full Text] e141

Lee, T.; Tjoelker, M. G.; Reich, P. B.; Russelle, M. P.; Contrasting growth responses of an N2-fixing and non-fixing forb to elevated CO2: dependence on soil N supply. Plant and Soil 255:475-486. 2003 [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

Mueller, K. E.; Hobbie, S. E.; Tilman, D. and Reich, P. B. (2013); Effects of plant diversity, N fertilization, and elevated carbon dioxide on grassland soil N cycling in a long-term experiment.; Global Change Biology, 19: 12491261. doi: 10.1111/gcb.12096 2013 [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

Nico Eisenhauer, Tomasz Dobies, Simone Cesarz, Sarah E. Hobbie, Ross J. Meyer, Kally Worm, and Peter B. Reich; Plant diversity effects on soil food webs are stronger than those of elevated CO2 and N deposition in a long-term grassland experiment; PNAS 2013 110 (17) 6889-6894; doi:10.1073/pnas.1217382110 2013 [Full Text] e141

Reich, P.; Elevated CO2 reduces losses of plant diversity caused by nitrogen deposition. Science 326:1399 2009 [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.; Hungate, B.; Luo, Y.; "Carbon-Nitrogen Interactions in Terrestrial Ecosystems in Response to Rising Atmospheric CO2. Annual Review of Ecologyk Evolution, and Systematics 37:611-636." 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.; 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

Reich, Peter B.; Hobbie, Sarah E.; Decade-long soil nitrogen constraint on the CO2 fertilization of plant biomass.; Nature Climate Change 2013 3:278-282 doi:10.1038/nclimate1694 2013 [Full Text] e141

Reid, J. P.; Adair, E. C.; Hobbie, S. E.; Reich, P. B.; Biodiversity, nitrogen deposition and CO2 affect grassland soil carbon cycling but not storage. 2012. Ecosystems 15(4):580-590. 2012 [Full Text] e141

Reid, Joseph Pignatello; Non-equilibrium dynamics of ecosystem processes in a changing world; 2013 ; Ph.D. dissertation; University of Minnesota Digital Conservancy Permanent URL http://hdl.handle.net/11299/159915 2013 [Full Text] e141

Strengbom, J.; Reich, P. B.; Elevated [CO2] and increased N supply reduce leaf disease and related photosynthetic impacts on Solidago rigida. OECOLOGIA 149:519-525. 2006 [Abstract] [Full Text] e141

Strengbom, Joachim; Reich, Peter B.; Elevated [C02] and increased N supply reduce leaf disease and related photosynthetic impacts on Solidago rigida. Oecologia: Global Change Ecology. 149:519-525 2006 [Full Text] e141

Tjoelker, M.; Oleksyn, J.; Lee, T. D.; Reich, P. B.; Direct inhibition of leaf dark respiration by elevated CO2 is minor in 12 grassland species. New Phytologist 150(2):419-424. 2001 [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

Wright, A.; Schnitzer, S.; Dickie, I. A.; Gunderson, A. R.; Pinter, G. A.; Mangan, S. A.; Reich, P. B.; Complex facilitation and competition in a temperate grassland: loss of plant diversity and elevated CO2 have divergent and opposite effects on oak establishment. 2013. Oecologia 171:449-458. DOI 10.1007/s00442-012-2420-y 2013 [Full Text] e141

Xu, Meiying; He, Zhili; Deng, Ye; Wu, Liyou; van Nostrand, Joy D.; Hobbie, Sarah E.; Reich, Peter B.; Zhou, Jizhong; Elevated CO2 influences microbial carbon and nitrogen cycling; BMC Microbiology; Volume 13:124; doi:10.1186/1471-2180-13-124 2013 [Full Text] e141

van Groenigen, Kees-Jan; Six, Johan; Hungate, Bruce A.; de Graaff, Marie-Anne; van Breemen, Nico; van Kessel, Chris; Element interactions limit soil carbon storage. PNAS. 103:6571-6574 2006 [Full Text] e141