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C4 grasses prosper as carbon dioxide eliminates desiccation in warmed semi-arid grassland


Global warming is predicted to induce desiccation in many world regions through increases in evaporative demand1,2,3. Rising CO2 may counter that trend by improving plant water-use efficiency4,5. However, it is not clear how important this CO2-enhanced water use efficiency might be in offsetting warming-induced desiccation because higher CO2 also leads to higher plant biomass, and therefore greater transpirational surface2,6,7. Furthermore, although warming is predicted to favour warm-season, C4 grasses, rising CO2 should favour C3, or cool-season plants8. Here we show in a semi-arid grassland that elevated CO2 can completely reverse the desiccating effects of moderate warming. Although enrichment of air to 600 p.p.m.v. CO2 increased soil water content (SWC), 1.5/3.0 °C day/night warming resulted in desiccation, such that combined CO2 enrichment and warming had no effect on SWC relative to control plots. As predicted, elevated CO2 favoured C3 grasses and enhanced stand productivity, whereas warming favoured C4 grasses. Combined warming and CO2 enrichment stimulated above-ground growth of C4 grasses in 2 of 3 years when soil moisture most limited plant productivity. The results indicate that in a warmer, CO2-enriched world, both SWC and productivity in semi-arid grasslands may be higher than previously expected.

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Figure 1: Responses of SWC to CO 2 and warming.
Figure 2: Plant biomass responses to CO 2 and warming.
Figure 3: Response of biomass enhancement ratio to soil matric potential.
Figure 4: Percentage changes in ETref for a grass surface as affected by temperature and changes in rc.


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We thank D. Smith for installation and operation of the PHACE experiment, E. Hardy for assistance in installation, A. Eden and C. Brooks for data collection and analysis, F. Miglietta for advice and help on installation of the FACE system, and R. Seager, A. Leakey, B. Cook and G. Wang for comments on the manuscript. The work was supported by the US Department of Agriculture-Agricultural Research Service Climate Change, Soils & Emissions Program, the US Department of Agriculture-Cooperative State Research, Education, and Extension Service Soil Processes Program (grant no. 2008-35107-18655), the US Department of Energy’s Office of Science (Biological and Environmental Research) through the Western Regional Center of the National Institute for Climatic Change Research at Northern Arizona University, and the National Science Foundation (DEB no. 1021559). Mention of commercial products is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the USDA.

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Authors and Affiliations



J.A.M., E.P., D.M.B., B.A.K., D.G.W. and M.W. conceived the study. J.A.M., D.R.L., E.P., D.M.B., Y.C., D.G.W., J.H.-W. and F.A.D. performed the experiment. B.A.K. designed the warming system and conducted the evapotranspiration analysis. J.A.M. wrote the paper and the remaining authors contributed to the writing. Statistical analyses using SAS/STAT software, version 9.2, Proc GLIMMIX were performed by M.W. and J.A.M. The regression analyses using JMP software were performed by D.M.B. and J.A.M. Figures were developed by D.R.L.

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Correspondence to Jack A. Morgan.

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Supplementary information

Supplementary Information

This file comprises 3 appendices: I Experimental Methods and System Performance; II Soil Water Content and III Global Change Treatments and Plant Responses. The file also contains Supplementary Figures 1-5 with legends, Supplementary Tables 1-2 and additional references. (PDF 613 kb)

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Morgan, J., LeCain, D., Pendall, E. et al. C4 grasses prosper as carbon dioxide eliminates desiccation in warmed semi-arid grassland. Nature 476, 202–205 (2011).

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