Abstract
Severe droughts in the Northern Hemisphere cause a widespread decline of agricultural yield, the reduction of forest carbon uptake, and increased CO2 growth rates in the atmosphere. Plants respond to droughts by partially closing their stomata to limit their evaporative water loss, at the expense of carbon uptake by photosynthesis. This trade-off maximizes their water-use efficiency (WUE), as measured for many individual plants under laboratory conditions and field experiments. Here we analyse the 13C/12C stable isotope ratio in atmospheric CO2 to provide new observational evidence of the impact of droughts on the WUE across areas of millions of square kilometres and spanning one decade of recent climate variability. We find strong and spatially coherent increases in WUE along with widespread reductions of net carbon uptake over the Northern Hemisphere during severe droughts that affected Europe, Russia and the United States in 2001–2011. The impact of those droughts on WUE and carbon uptake by vegetation is substantially larger than simulated by the land-surface schemes of six state-of-the-art climate models. This suggests that drought-induced carbon–climate feedbacks may be too small in these models and improvements to their vegetation dynamics using stable isotope observations can help to improve their drought response.
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Acknowledgements
This work used eddy covariance data acquired by the FLUXNET community. We acknowledge the financial support to the eddy covariance data harmonization provided by CarboEuropeIP, FAO-GTOS-TCO, iLEAPS, Max Planck Institute for Biogeochemistry, National Science Foundation, University of Tuscia, Université Laval and Environment Canada, and US Department of Energy and the database development and technical support from Berkeley Water Center, Lawrence Berkeley National Laboratory, Microsoft Research eScience, Oak Ridge National Laboratory, University of California Berkeley, University of Virginia. Ru-Fyo data were provided by A. Varlagin and J. Kurbatova from the Russian Academy of Sciences. C. Montzka is acknowledged for providing a SoilGrids-ROSETTA-based set of soil-hydraulic properties for the JULES modelling effort. We thank J. C. Lin and B. M. Raczka for their contributions to the CLM4.5 work. We thank S. E. Michel (INSTAAR) for the QA/QC of the δ¹³C data used in this study. C. Rödenbeck is acknowledged for providing additional information on gross ocean exchange. I.R.vdV. was financially supported by the Netherlands Organization for Scientific Research (NWO-VIDI 864.08.012) and by the National Computing Facilities Foundation (NCF project SH-060) for the use of supercomputing facilities. H.F.D. was supported by the US Department of Energy’s Office of Science, Terrestrial Ecosystem Science Program (award no. DE-SC0010624), and by the NASA CMS Project (award no. NNX16AP33G). P.L.V. was supported by the UK Natural Environment Research Council (NERC) funding of the National Centre for Atmospheric Science (NCAS). A.V. and P.L.V. were supported by the NERC project IMPETUS (ref. NE/L010488/1). W.P. and E.vS. received financial support from the European Research Council’s project ASICA (CoG 649087). We thank the NOAA Climate Program Office’s Atmospheric Chemistry, Carbon Cycle, and Climate (AC4) program for support, including that for the collection and analysis of CO2 and δ¹³C observations used in this study. We thank P. R. Rayner for very helpful comments on the manuscript.
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W.P., I.R.vdV. and J.B.M. designed the study. I.R.vdV., K.S., W.P., E.vS., I.T.vdL.-L., P.L.V., A.V., P.C., D.W., M.S., D.Z., H.F.D. and M.K.vdM. built the inverse and forward modelling frameworks. P.P.T., B.V. and J.W.C.W. were responsible for the δ¹³C and CO2 measurement programme. W.P., I.R.vdV. and E.vS. performed the analysis and wrote the main text. All the authors provided input to the final manuscript.
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Peters, W., van der Velde, I.R., van Schaik, E. et al. Increased water-use efficiency and reduced CO2 uptake by plants during droughts at a continental scale. Nature Geosci 11, 744–748 (2018). https://doi.org/10.1038/s41561-018-0212-7
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DOI: https://doi.org/10.1038/s41561-018-0212-7
