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Contrasting responses of woody and grassland ecosystems to increased CO2 as water supply varies

Nature Ecology & Evolution volume 6, pages 315–323 (2022)Cite this article

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Abstract

Experiments show that elevated atmospheric CO2 (eCO2) often enhances plant photosynthesis and productivity, yet this effect varies substantially and may be climate sensitive. Understanding if, where and how water supply regulates CO2 enhancement is critical for projecting terrestrial responses to increasing atmospheric CO2 and climate change. Here, using data from 14 long-term ecosystem-scale CO2 experiments, we show that the eCO2 enhancement of annual aboveground net primary productivity is sensitive to annual precipitation and that this sensitivity differs between woody and grassland ecosystems. During wetter years, CO2 enhancement increases in woody ecosystems but declines in grass-dominated systems. Consistent with this difference, woody ecosystems can increase leaf area index in wetter years more effectively under eCO2 than can grassland ecosystems. Overall, and across different precipitation regimes, woody systems had markedly stronger CO2 enhancement (24%) than grasslands (13%). We developed an empirical relationship to quantify aboveground net primary productivity enhancement on the basis of changes in leaf area index, providing a new approach for evaluating eCO2 impacts on the productivity of terrestrial ecosystems.

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Fig. 1: Relationships between eCO2 enhancement of ANPP and iPPT.
Fig. 2: Mean responses of EAPPAV to MAP across multiple ecosystems.
Fig. 3: The relationship between EAPP and ELAI.

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Data availability

Data collated and used for analyses, figures and tables of this study are available for access (https://doi.org/10.2737/RDS-2021-0093). The processed data underlying Figs. 1–3 and Extended Data Figs. 1–4 are available in the Source Data files. Full description of the original datasets is provided in Supplementary Tables 1–4. Source data are provided with this paper.

References

  1. Keenan, T. F. et al. Recent pause in the growth rate of atmospheric CO2 due to enhanced terrestrial carbon uptake. Nat. Commun. 7, 13428 (2016).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  2. Fatichi, S. et al. Partitioning direct and indirect effects reveals the response of water-limited ecosystems to elevated CO2. Proc. Natl Acad. Sci. USA 113, 12757–12762 (2016).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  3. Smith, W. K. et al. Large divergence of satellite and Earth system model estimates of global terrestrial CO2 fertilization. Nat. Clim. Change 6, 306–310 (2016).

    Article  Google Scholar 

  4. Schimel, D., Stephens, B. B. & Fisher, J. B. Effect of increasing CO2 on the terrestrial carbon cycle. Proc. Natl Acad. Sci. USA 112, 436–441 (2015).

    Article  CAS  PubMed  Google Scholar 

  5. Norby, R. J. et al. Forest response to elevated CO2 is conserved across a broad range of productivity. Proc. Natl Acad. Sci. USA 102, 18052–18056 (2005).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  6. Mooney, H. A., Drake, B. G., Luxmoore, R. J., Oechel, W. C. & Pitelka, L. F. Predicting ecosystem responses to elevated CO2 concentrations. Bioscience 41, 96–104 (1991).

    Article  Google Scholar 

  7. Leakey, A. D. B. et al. Elevated CO2 effects on plant carbon, nitrogen, and water relations: six important lessons from FACE. J. Exp. Bot. 60, 2859–2876 (2009).

    Article  CAS  PubMed  Google Scholar 

  8. Jackson, R. B., Sala, O. E., Field, C. B. & Mooney, H. A. CO2 alters water use, carbon gain, and yield for the dominant species in a natural grassland. Oecologia 98, 257–262 (1994).

    Article  CAS  PubMed  Google Scholar 

  9. Morgan, J. A. et al. Water relations in grassland and desert ecosystems exposed to elevated atmospheric CO2. Oecologia 140, 11–25 (2004).

    Article  CAS  PubMed  Google Scholar 

  10. Keenan, T. F. et al. Increase in forest water-use efficiency as atmospheric carbon dioxide concentrations rise. Nature 499, 324–327 (2013).

    Article  CAS  PubMed  Google Scholar 

  11. Donohue, R. J., Roderick, M. L., McVicar, T. R. & Farquhar, G. D. Impact of CO2 fertilization on maximum foliage cover across the globe’s warm, arid environments. Geophys. Res. Lett. 40, 3031–3035 (2013).

    Article  CAS  Google Scholar 

  12. Poulter, B. et al. Contribution of semi-arid ecosystems to interannual variability of the global carbon cycle. Nature 509, 600–603 (2014).

    Article  CAS  PubMed  Google Scholar 

  13. Ahlström, A. et al. The dominant role of semi-arid ecosystems in the trend and variability of the land CO2 sink. Science 348, 895–899 (2015).

    Article  PubMed  Google Scholar 

  14. Karnosky, D. F. et al. Tropospheric O3 moderates responses of temperate hardwood forests to elevated CO2: a synthesis of molecular to ecosystem results from the Aspen FACE project. Funct. Ecol. 17, 289–304 (2003).

    Article  Google Scholar 

  15. Norby, R. J. & Zak, D. R. Ecological lessons from free-air CO2 enrichment (FACE) experiments. Annu. Rev. Ecol. Syst. 42, 181–203 (2011).

    Article  Google Scholar 

  16. Nowak, R. S., Ellsworth, D. S. & Smith, S. D. Functional responses of plants to elevated atmospheric CO2— do photosynthetic and productivity data from FACE experiments support early predictions? N. Phytol. 162, 253–280 (2004).

    Article  Google Scholar 

  17. Ainsworth, E. A. & Long, S. P. What have we learned from fifteen years of free air carbon dioxide enrichment (FACE)? A meta-analytic review of the responses of photosynthesis, canopy properties and plant production to rising CO2. N. Phytol. 165, 351–372 (2004).

    Article  Google Scholar 

  18. 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. N. Phytol. 150, 405–418 (2001).

    Article  CAS  Google Scholar 

  19. Warren, J. M. et al. Ecohydrological impact of reduced stomatal conductance in forests exposed to elevated CO2. Ecohydrology 4, 196–210 (2011).

    Article  Google Scholar 

  20. Morgan, J. A. et al. CO2 enhances productivity, alters species composition, and reduces digestibility of shortgrass steppe vegetation. Ecol. Appl. 14, 208–219 (2004).

    Article  Google Scholar 

  21. Dukes, J. S. et al. Responses of grassland production to single and multiple global environmental changes. PLoS Biol. 3, 1829–1839 (2005).

    Article  CAS  Google Scholar 

  22. Hovenden, M. J., Newton, P. C. D. & Wills, K. E. Seasonal not annual rainfall determines grassland biomass response to carbon dioxide. Nature 511, 583–586 (2014).

    Article  CAS  PubMed  Google Scholar 

  23. Reich, P. B., Hobbie, S. E. & Lee, T. D. Plant growth enhancement by elevated CO2 eliminated by joint water and nitrogen limitation. Nat. Geosci. 7, 920–924 (2014).

    Article  CAS  Google Scholar 

  24. Hebeisen, T. et al. Growth response of Trifolium repens L. and Lolium perenne L. as monocultures and bi-species mixture to free air CO2 enrichment and management. Glob. Change Biol. 3, 149–160 (1997).

    Article  Google Scholar 

  25. Prentice, I. C., Dong, N., Gleason, S. M., Maire, V. & Wright, I. J. Balancing the cost of carbon gain and water transport: testing a new theoretical framework for plant functional ecology. Ecol. Lett. 17, 82–91 (2014).

    Article  PubMed  Google Scholar 

  26. Ellsworth, D. S. et al. Elevated CO2 does not increase eucalypt forest productivity on a low-phosphorus soil. Nat. Clim. Change 7, 279–282 (2017).

    Article  CAS  Google Scholar 

  27. Ponce Campos, G. E. et al. Ecosystem resilience despite large-scale altered hydroclimatic conditions. Nature 494, 350–352 (2014).

    Google Scholar 

  28. Oren, R., Ewers, B. E., Todd, P., Phillips, N. & Katul, G. Water balance delineates the soil layer in which moisture affects canopy conductance. Ecol. Appl. 8, 990–1002 (1998).

    Article  Google Scholar 

  29. Stanton, N. L. The underground in grasslands. Annu. Rev. Ecol. Syst. 19, 573–589 (1988).

    Article  Google Scholar 

  30. Owensby, C. E., Ham, J. M., Knapp, A. K. & Auen, L. M. Biomass production and species composition change in a tallgrass prairie ecosystem after long-term exposure to elevated atmospheric CO2. Glob. Change Biol. 5, 497–506 (1999).

    Article  Google Scholar 

  31. McCarthy, H. R. et al. Temporal dynamics and spatial variability in the enhancement of canopy leaf area under elevated atmospheric CO2. Glob. Change Biol. 13, 2479–2497 (2007).

    Article  Google Scholar 

  32. McCathy, H. R., Oren, R., Finzi, A. C. & Jonsen, K. H. Canopy leaf area constrains CO2-induced enhancement of productivity and partitioning among aboveground carbon pools. Proc. Natl Acad. Sci. USA 103, 19356–19361 (2006).

    Article  Google Scholar 

  33. Tor-ngern, P. et al. Increases in atmospheric CO2 have little influence on transpiration of a temperate forest canopy. N. Phytol. 205, 518–525 (2015).

    Article  CAS  Google Scholar 

  34. Naumburg, E. et al. Photosynthetic responses of Mojave Desert shrubs to free air CO2 enrichment are greatest during wet years. Glob. Change Biol. 9, 276–285 (2003).

    Article  Google Scholar 

  35. Housman, D. C. et al. Increases in desert shrub productivity under elevated carbon dioxide vary with water availability. Ecosystems 9, 374–385 (2006).

    Article  Google Scholar 

  36. Warren, J. M., Norby, R. J. & Wullschleger, S. D. Elevated CO2 enhances leaf senescence during extreme drought in a temperate forest. Tree Physiol. 31, 117–130 (2011).

    Article  PubMed  Google Scholar 

  37. Ellsworth, D. S. et al. Elevated CO2 affects photosynthetic responses in canopy pine and subcanopy deciduous trees over 10 years: a synthesis from Duke Face. Glob. Change Biol. 18, 223–242 (2012).

    Article  Google Scholar 

  38. Mueller, K. E. et al. Impacts of warming and elevated CO2 on a semi-arid grassland are non-additive, shift with precipitation, and reverse over time. Ecol. Lett. 19, 956–966 (2016).

    Article  CAS  PubMed  Google Scholar 

  39. Morgan, J. A., Milchunas, D. G., LeCain, D. R., West, M. & Mosier, A. R. Carbon dioxide enrichment alters plant community structure and accelerates shrub growth in the shortgrass steppe. Proc. Natl Acad. Sci. USA 104, 14724–14729 (2007).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  40. Farquhar, G. D. et al. A biochemical model of photosynthetic CO2 assimilation in leaves of C3 species. Planta 149, 78–90 (1980).

    Article  CAS  PubMed  Google Scholar 

  41. De Graaff, M. A., Van Groenigen, K. J., Six, J., Hungate, B. & Van Kessel, C. Interactions between plant growth and soil nutrient cycling under elevated CO2: a meta-analysis. Glob. Change Biol. 12, 2077–2091 (2006).

    Article  Google Scholar 

  42. Jiang, M. et al. The fate of carbon in a mature forest under carbon dioxide enrichment. Nature 580, 227–231 (2020).

    Article  CAS  PubMed  Google Scholar 

  43. Bader, M. K. F. et al. Central European hardwood trees in a high-CO2 future: synthesis of an 8-year forest canopy CO2 enrichment project. J. Ecol. 101, 1509–1519 (2013).

    Article  CAS  Google Scholar 

  44. Klein, T. et al. Growth and carbon relations of mature Picea abies trees under 5 years of free-air CO2 enrichment. J. Ecol. 104, 1720–1733 (2016).

    Article  CAS  Google Scholar 

  45. McCarthy, M. C. & Enquist, B. J. Consistency between an allometric approach and optimal partitioning theory in global patterns of plant biomass allocation. Funct. Ecol. 21, 713–720 (2007).

    Article  Google Scholar 

  46. Palmroth, S. et al. Aboveground sink strength in forests controls the allocation of carbon below ground and its CO2-induced enhancement. Proc. Natl Acad. Sci. USA 103, 19362–19367 (2006).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  47. Wolf, A., Field, C. B. & Berry, J. A. Allometric growth and allocation in forests: a perspective from FLUXNET. Ecol. Appl. 21, 1546–1556 (2011).

    Article  PubMed  Google Scholar 

  48. Hovenden, M. J. et al. Globally consistent influences of seasonal precipitation limit grassland biomass response to elevated CO2. Nat. Plants 5, 167–173 (2019).

    Article  CAS  PubMed  Google Scholar 

  49. Graven, H. D. et al. Enhanced seasonal exchange of CO2 by northern ecosystems since 1960. Science 341, 1085–1089 (2013).

    Article  CAS  PubMed  Google Scholar 

  50. Phillips, O. L. et al. Increasing dominance of large lianas in Amazonian forests. Nature 418, 770–774 (2002).

    Article  CAS  PubMed  Google Scholar 

  51. Zotz, G., Cueni, N. & Körner, C. In situ growth stimulation of a temperate zone liana (Hedera helix) in elevated CO2. Funct. Ecol. 20, 763–769 (2006).

    Article  Google Scholar 

  52. Smith, S. D. et al. Elevated CO2 increases productivity and invasive species success in an arid ecosystems. Nature 408, 79–81 (2000).

    Article  CAS  PubMed  Google Scholar 

  53. Saintilan, N. & Rogers, K. Woody plant encroachment of grasslands: a comparison of terrestrial and wetland settings. N. Phytol. 205, 1062–1070 (2015).

    Article  Google Scholar 

  54. Pan, Y. et al. A large and persistent carbon sink in the world’s forests. Science 333, 988–003 (2011).

    Article  CAS  PubMed  Google Scholar 

  55. Hubau, W. et al. Asynchronous carbon sink saturation in African and Amazonian tropical forests. Nature 579, 80–87 (2020).

    Article  CAS  PubMed  Google Scholar 

  56. Flato G. et al. in Climate Change 2013: The Physical Science Basis (eds Stocker, T. F. et al.) 741–866 (Cambridge Univ. Press, 2013).

  57. https://www.cedarcreek.umn.edu/research/experiments/e141

  58. https://facedata.ornl.gov/ornl/

  59. Hymus, G. J. et al. Effects of elevated atmospheric CO2 on net ecosystem CO2 exchange of a scrub-oak ecosystem. Glob. Change Biol. 9, 1802–1812 (2003).

    Article  Google Scholar 

  60. Riley, R. D., Lambert, P. C. & Abo-Zaid, G. Meta-analysis of individual participant data: rationale, conduct, and reporting. Br. Med. J. 340, c221 (2010).

    Article  Google Scholar 

  61. Millar, R. B. & Anderson, M. J. Remedies for pseudo-replication. Fish. Res. 70, 397–407 (2004).

    Article  Google Scholar 

  62. Cashman, K. D. et al. Improved dietary guidelines for vitamin D: application of individual participant data (IPD)-level meta-regression analyses. Nutrients 9, 469 (2017).

    Article  PubMed Central  Google Scholar 

Download references

Acknowledgements

The authors acknowledge the FACE experiments, scientists’ investigations and publications that provide data for this study. Y.P. acknowledges the support of Bullard Fellowship at Harvard University. O.L.P acknowledges support from the Royal Society and the European Research Council ERC (AdG grant 291585). R.S.N. and R.J.N acknowledge support from the US Department of Energy, Office of Science, Biological and Environmental Research Office. R.O. acknowledges support from Jane and Aatos Erkko 375th Anniversary Fund through the University of Helsinki. The contribution of P.B.R. was supported by the US NSF Biological Integration Institutes grant DBI-2021898. The lead author is grateful to J. Morgan and J. Nösberger for valuable comments and insights contributed to earlier drafts of the manuscript. This study was originally inspired by a synthesis study published in 2004 by Nowak et al.16.

Author information

Authors and Affiliations

  1. USDA Forest Service, Northern Research Station, Durham, NH, USA

    Yude Pan & David Y. Hollinger

  2. The Woods Institute for the Environment and at the Precourt Institute for Energy, Stanford University, Stanford, CA, USA

    Robert B. Jackson

  3. University of Leeds, School of Geography, Leeds, UK

    Oliver L. Phillips

  4. Department of Natural Resources and Environmental Science, University of Nevada, Reno, NV, USA

    Robert S. Nowak

  5. Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN, USA

    Richard J. Norby

  6. Nicholas School of the Environment and Pratt School of Engineering, Duke University, Durham, NC, USA

    Ram Oren

  7. Department of Forest Science, University of Helsinki, Helsinki, Finland

    Ram Oren

  8. Department of Forest Resources, University of Minnesota, St Paul, MN, USA

    Peter B. Reich

  9. Institute for Global Change Biology and School for the Environment and Sustainability, University of Michigan, Ann Arbor, MI, USA

    Peter B. Reich

  10. Western Sydney University, Penrith, New South Wales, Australia

    Peter B. Reich

  11. ETH Zurich, Institute of Agricultural Science, Zurich, Switzerland

    Andreas Lüscher

  12. Agroscope, Forage Production and Grassland Systems, Zurich, Switzerland

    Andreas Lüscher

  13. Biological, Geological and Environmental Sciences, Cleveland State University, Cleveland, OH, USA

    Kevin E. Mueller

  14. Department of Agronomy, Throckmorton Plant Sciences Center, Kansas State University, Manhattan, KS, USA

    Clenton Owensby

  15. Woodwell Climate Research Center, Falmouth, MA, USA

    Richard Birdsey

  16. Department of Plant and Soil Sciences, University of Delaware, Newark, DE, USA

    John Hom

  17. Center for Ecosystem Science and Society, Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ, USA

    Yiqi Luo

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  1. Yude Pan
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Contributions

Y.P. assembled and analysed the data and wrote the manuscript; R.B.J., D.Y.H., O.L.P. and R.S.N. provided concepts and substantial editing of the manuscript; R.J.N., R.O., P.B.R., A.L., K.E.M. and C.O. were the major investigators for the eCO2 experiments, providing the data, insightful comments and editing; R.B., J.H. and Y.L. edited and provided comments on the manuscript.

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Correspondence to Yude Pan.

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Extended data

Extended Data Fig. 1 Responses of C3 and C4 grasses to eCO2.

(a) EAPP responses of C3 and C4 grasses to annual precipitation (iPPT); (b) the Z-score analysis for C3 grasses, and a linear regression; and (c) the Z-scores analysis for C4 grasses; there is not an obvious relationship between EAPP and iPPT.

Source data

Extended Data Fig. 2 Sensitivity of ANPP enhancement to annual precipitation (slopes of the linear functions (Supplementary Table 5).

(a) Across woody and across (b) grassland ecosystems. A positive slope means EAPP increasing with increasing iPPT at a given site; a negative slope EAPP decreasing with increasing iPPT. Error bars are the standard errors (SEs) for slopes and MAP, respectively. The symbol ‘*’ is used for sites with a linear regression at *p = 0.1. Arrows show MAP levels when slopes approach zero in woody and grassland ecosystems.

Source data

Extended Data Fig. 3 Mean ANPP enhancements affected by eCO2 levels.

(a) Mean values of EAPP for all sampling years and all sites (EAPPAVE) of woody (solid symbols) and grassland (open symbols) ecosystems; EAPP responses to iPPT are not significantly different between woody and grassland ecosystems (t-test: p = 0.055); (b) EAPPAVE of woody and grassland ecosystems after adjusting higher eCO2 concentrations used in experiments to 550 ppm based on the Farquhar model (Extended Data Fig. 4); EAPP responses to iPPT are significantly different between woody and grassland ecosystems (t-test: p = 0.011). Error bars represent standard deviations (SDs).

Source data

Extended Data Fig. 4 Effects of CO2 levels on canopy photosynthetic rates illustrated by the Farquhar model.

Y-axis shows the impact (scalar) of intercellular CO2 levels on canopy photosynthesis rates, given an assumption of optimal intercellular CO2 level being close to the atmospheric level. Relatively higher CO2 concentrations were used in 6 enrichment experiments (600–720 ppm) compared to the CO2 concentration (~550 ppm) used in forest ecosystems.

Source data

Supplementary information

Supplementary Information

Supplementary Discussion, Tables 1–9 and Figs. 1–3.

Reporting Summary

Source data

Source Data Fig. 1

Experimental years, annual precipitation, aboveground NPP CO2 enhancement ratios (EAPP) derived from 14 CO2 experiments of woody and grassland ecosystems, Z scores of EAPP and annual precipitations of experimental data.

Source Data Fig. 2

Mean annual precipitation and mean ecosystem EAPP of experimental sites.

Source Data Fig. 3

The enhancement ratios of leaf area index (ELAI) and enhancement ratios of aboveground NPP (EAPP) from experimental sites.

Source Data Extended Data Fig. 1

Annual precipitation and CO2 enhancement ratios (EAPP) of C3 and C4 plants; Z scores of annual precipitation, Z scores of EAPP of C3 and C4 plants, respectively.

Source Data Extended Data Fig. 2

Mean site annual precipitation (MAP) and slopes of linear functions of CO2 enhancement ratios.

Source Data Extended Data Fig. 3

Annual precipitation, aboveground NPP enhancement ratios (EAPP) under different CO2 levels used in the experimental sites; annual precipitation and EAPP after adjusting CO2 levels to 550 ppm.

Source Data Extended Data Fig. 4

Results of Farquhar models and values for adjusting CO2 levels.

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Pan, Y., Jackson, R.B., Hollinger, D.Y. et al. Contrasting responses of woody and grassland ecosystems to increased CO2 as water supply varies. Nat Ecol Evol 6, 315–323 (2022). https://doi.org/10.1038/s41559-021-01642-6

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