Vegetation modulates Earth’s water, energy and carbon cycles. How its functions might change in the future largely depends on how it copes with droughts1,2,3,4. There is evidence that, in places and times of drought, vegetation shifts water uptake to deeper soil5,6,7 and rock8,9 moisture as well as groundwater10,11,12. Here we differentiate and assess plant use of four types of water sources: precipitation in the current month (source 1), past precipitation stored in deeper unsaturated soils and/or rocks (source 2), past precipitation stored in groundwater (source 3, locally recharged) and groundwater from precipitation fallen on uplands via river–groundwater convergence toward lowlands (source 4, remotely recharged). We examine global and seasonal patterns and drivers in plant uptake of the four sources using inverse modelling and isotope-based estimates. We find that (1), globally and annually, 70% of plant transpiration relies on source 1, 18% relies on source 2, only 1% relies on source 3 and 10% relies on source 4; (2) regionally and seasonally, source 1 is only 19% in semi-arid, 32% in Mediterranean and 17% in winter-dry tropics in the driest months; and (3) at landscape scales, source 2, taken up by deep roots in the deep vadose zone, is critical in uplands in dry months, but source 4 is up to 47% in valleys where riparian forests and desert oases are found. Because the four sources originate from different places and times, move at different spatiotemporal scales and respond with different sensitivity to climate and anthropogenic forces, understanding the space and time origins of plant water sources can inform ecosystem management and Earth system models on the critical hydrological pathways linking precipitation to vegetation.
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All model input data are generated by government and research agencies and are in the public domain. Links to download these data are provided in Supplementary Table 2. Modelled monthly transpiration and source contributions (sources 1, 2, 3 and 4) for each continent and month can be downloaded at the following public repository via ftp: http://thredds-gfnl.usc.es/thredds/catalog/DATA_TRANSPSOURCES/catalog.html. The isotope compilation can also be found in an Excel spreadsheet at the above ftp site.
Our model code, written in Fortran, was uploaded to GitHub: https://github.com/gmiguez/MMF-HYDROMODEL.
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This work was supported by grants from the European Commission Seventh Framework Programme (EartH2Observe 603608) to G.M.-M. and grants from the US National Science Foundation (NSF-EAR-825813 and AGS-1852707) to Y.F. All computation was performed at CESGA (Centro de Supercomputación de Galicia) Supercomputer Center at the Universidade de Santiago de Compostela in Galicia, Spain. We thank FLUXNET and the GRDC and their contributors worldwide for providing ET and river flow observations for model validations.
The authors declare no competing interests.
Peer review information Nature thanks Adrià Barbeta, Timothy Brodribb, Youri Rothfuss, Ruud Van der Ent and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Extended data figures and tables
(a) Source-2 and (b) Source-3+4 (undistinguished isotopically) during dry periods (best sampled). Where species are sampled at the same location (dots overlapping), the highest is displayed on the top.
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Miguez-Macho, G., Fan, Y. Spatiotemporal origin of soil water taken up by vegetation. Nature 598, 624–628 (2021). https://doi.org/10.1038/s41586-021-03958-6