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Climatic controls of decomposition drive the global biogeography of forest-tree symbioses

Abstract

The identity of the dominant root-associated microbial symbionts in a forest determines the ability of trees to access limiting nutrients from atmospheric or soil pools1,2, sequester carbon3,4 and withstand the effects of climate change5,6. Characterizing the global distribution of these symbioses and identifying the factors that control this distribution are thus integral to understanding the present and future functioning of forest ecosystems. Here we generate a spatially explicit global map of the symbiotic status of forests, using a database of over 1.1 million forest inventory plots that collectively contain over 28,000 tree species. Our analyses indicate that climate variables—in particular, climatically controlled variation in the rate of decomposition—are the primary drivers of the global distribution of major symbioses. We estimate that ectomycorrhizal trees, which represent only 2% of all plant species7, constitute approximately 60% of tree stems on Earth. Ectomycorrhizal symbiosis dominates forests in which seasonally cold and dry climates inhibit decomposition, and is the predominant form of symbiosis at high latitudes and elevation. By contrast, arbuscular mycorrhizal trees dominate in aseasonal, warm tropical forests, and occur with ectomycorrhizal trees in temperate biomes in which seasonally warm-and-wet climates enhance decomposition. Continental transitions between forests dominated by ectomycorrhizal or arbuscular mycorrhizal trees occur relatively abruptly along climate-driven decomposition gradients; these transitions are probably caused by positive feedback effects between plants and microorganisms. Symbiotic nitrogen fixers—which are insensitive to climatic controls on decomposition (compared with mycorrhizal fungi)—are most abundant in arid biomes with alkaline soils and high maximum temperatures. The climatically driven global symbiosis gradient that we document provides a spatially explicit quantitative understanding of microbial symbioses at the global scale, and demonstrates the critical role of microbial mutualisms in shaping the distribution of plant species.

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Data availability

Information regarding symbiotic guild assignments, model selection (including global rasters of our model projections for ectomycorrhizal, arbuscular mycorrhizal and N-fixer proportion of tree basal area) and analyses is available as Supplementary Data. The GFBi database is available upon written request at https://www.gfbinitiative.org/datarequest. Any other relevant data are available from the corresponding authors upon reasonable request.

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Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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Acknowledgements

This work was made possible by the Global Forest Biodiversity Database, which represents the work of over 200 independent investigators and their public and private funding agencies (see Supplementary Acknowledgements).

Reviewer information

Nature thanks Martin Bidartondo, David Bohan and the other anonymous reviewer(s) for their contribution to the peer review of this work.

Author information

K.G.P. and T.W.C. conceived the study; T.W.C., J.L., P.B.R., G.N., S.d.-M., M.Z., N.P., B.H., X.Z. and C.Z. conceived and organized the GFBi database; K.G.P., B.S.S., G.D.A.W. and M.E.V.N. compiled the symbiosis database; B.S.S. carried out the primary data analysis; M.E.V.N. and D.R. contributed to data compilation and analysis; B.S.S., T.W.C., M.E.V.N. and K.G.P. wrote the initial manuscript; B.S.S., T.W.C., J.L., M.E.V.N., G.D.A.W., P.B.R., G.N., S.d.-M., M.Z., N.P., B.H., X.Z., C.Z. and K.G.P. made substantial revisions to all versions of the manuscript; all other named authors provided forest inventory data and commented on the manuscript.

Competing interests

The authors declare no competing interests.

Correspondence to T. W. Crowther or J. Liang or K. G. Peay.

Supplementary information

  1. Supplementary Information

    This file contains Supplementary Tables 1–8 and Supplementary Figures 1–26.

  2. Reporting Summary

  3. Supplementary Information

    This file contains Supplementary Acknowledgments.

  4. Supplementary Data

    This zip folder contains Supplementary Data files and a guide showing the climatic controls of decomposition drive the global biogeography of forest tree symbioses.

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About this article

Fig. 1: The global distribution of GFBi training data.
Fig. 2: A small number of environmental variables predict the majority of global turnover in forest symbiotic status.
Fig. 3: The distribution of forest symbiotic status across biomes is related to climatic controls over decomposition.
Fig. 4: Global maps of predicted forest-tree symbiotic state.

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