Letter | Published:

Water balance creates a threshold in soil pH at the global scale

Nature volume 540, pages 567569 (22 December 2016) | Download Citation

Abstract

Soil pH regulates the capacity of soils to store and supply nutrients, and thus contributes substantially to controlling productivity in terrestrial ecosystems1. However, soil pH is not an independent regulator of soil fertility—rather, it is ultimately controlled by environmental forcing. In particular, small changes in water balance cause a steep transition from alkaline to acid soils across natural climate gradients2,3. Although the processes governing this threshold in soil pH are well understood, the threshold has not been quantified at the global scale, where the influence of climate may be confounded by the effects of topography and mineralogy. Here we evaluate the global relationship between water balance and soil pH by extracting a spatially random sample (n = 20,000) from an extensive compilation of 60,291 soil pH measurements. We show that there is an abrupt transition from alkaline to acid soil pH that occurs at the point where mean annual precipitation begins to exceed mean annual potential evapotranspiration. We evaluate deviations from this global pattern, showing that they may result from seasonality, climate history, erosion and mineralogy. These results demonstrate that climate creates a nonlinear pattern in soil solution chemistry at the global scale; they also reveal conditions under which soils maintain pH out of equilibrium with modern climate.

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Acknowledgements

We thank P. Vitousek, S. Fendorf, X. Feng and C. Kouba for guidance and comments. Soil data were provided by multiple contributing organizations (Extended Data Table 1). Funding for E.W.S. was provided by a Graduate Research Fellowship from the United States National Science Foundation.

Author information

Author notes

    • J. E. Johnson

    Present address: Department of Global Ecology, Carnegie Institution for Science, Stanford, California, USA.

Affiliations

  1. Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, California, USA

    • E. W. Slessarev
    •  & J. P. Schimel
  2. Department of Environmental Science, Policy and Management, University of California, Berkeley, California, USA

    • Y. Lin
  3. Department of Geography, University of California, Santa Barbara, California, USA

    • N. L. Bingham
    •  & O. A. Chadwick
  4. Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona, USA

    • J. E. Johnson
  5. School of Atmospheric Sciences, Sun Yat-Sen University, Guangzhou, Guangdong, China

    • Y. Dai

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Contributions

Research was conceived by E.W.S., O.A.C., Y.L., N.L.B., J.P.S. and J.E.J. Data aggregation and processing tasks were shared by E.W.S., Y.L. and Y.D. Statistical analysis and chemical calculations were performed by E.W.S. The manuscript was written by E.W.S. with input from all authors.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to E. W. Slessarev.

Reviewer Information Nature thanks R. Merckx, S. Porder and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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https://doi.org/10.1038/nature20139

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