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Long-term multiple global change interactions amplify belowground carbon allocation

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Abstract

The strength and stability of the terrestrial carbon (C) sink depend critically on total belowground C allocation (TBCA), yet its long-term response to several co-occurring global change drivers remains largely unknown. Here, using an 11-year multifactor grassland experiment, we examined the individual and interactive effects of +2.5 °C warming, summer rainfall reduction, CO2 enrichment and nitrogen addition on the TBCA. Warming and CO2 enrichment increased TBCA by 17% and 16%, respectively, and these gains interacted with other drivers. The effects of CO2 enrichment were amplified under drought, the effects of warming strengthened with nitrogen addition, and the interaction between CO2 enrichment and nitrogen addition on TBCA strengthened over time from additive to synergistic. Moreover, TBCA was positively linked to soil respiration, C stock and plant nitrogen uptake. Together, TBCA responses to global change drivers are non-additive and shift over time, and elevated CO2 and warming promote soil C gains synergistically when nitrogen availability is high.

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Fig. 1: Conceptual diagram illustrating how four climate drivers influence TBCA in grasslands.
Fig. 2: TBCA in relation to CO2 enrichment, warming, drought and N addition.
Fig. 3: TBCA in relation to aboveground biomass C stock, root biomass C stock, total productivity and AB/RB.
Fig. 4: SEM depicting the effects of environmental change drivers on TBCA.
Fig. 5: TBCA in relation to soil respiration, soil C stock and plant N uptake.

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Data availability

All data supporting the findings of this study are available via figshare at https://doi.org/10.6084/m9.figshare.31321399 (ref. 48).

Code availability

All code used to generate the results and figures in this study are available via figshare at https://doi.org/10.6084/m9.figshare.31321399 (ref. 48).

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Funding

X.C. acknowledges support from the National Key R&D Program of China (2024YFF1309000), the National Natural Science Foundation of China (32401546) and the National Natural Science Foundation of China’s Excellent Young Scientists Fund (overseas). P.B.R. was supported by the US National Science Foundation’s ASCEND Biology Integration Institute (NSF-DBI-2021898) and by grants from the US National Science Foundation Long-Term Ecological Research Program since 1982 (including DEB-2425352 and DEB-1831944).

Author information

Authors and Affiliations

  1. State Key Laboratory for Development and Utilization of Forest Food Resources, Zhejiang A&F University, Hangzhou, China

    Xinli Chen 
    (陈信力)

  2. College of Grassland Science, Inner Mongolia Agricultural University, Hohhot, China

    Xinli Chen 
    (陈信力) & Han Y. H. Chen

  3. Institute for Global Change Biology, and School for Environment and Sustainability, University of Michigan, Ann Arbor, MI, USA

    Xinli Chen 
    (陈信力), Han Y. H. Chen, Katherine S. Rocci, Liting Zheng 
    (郑丽婷) & Peter B. Reich

  4. Key Laboratory of Carbon Sequestration and Emission Reduction in Agriculture and Forestry of Zhejiang Province, Zhejiang A&F University, Hangzhou, China

    Xinli Chen 
    (陈信力)

  5. Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO, USA

    Katherine S. Rocci

  6. Department of Forest Resources, University of Minnesota, St Paul, MN, USA

    Kally Worm & Peter B. Reich

  7. Hawkesbury Institute for the Environment, Western Sydney University, Penrith, New South Wales, Australia

    Peter B. Reich

Authors

  1. Xinli Chen 
    (陈信力)

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Contributions

P.B.R. designed the TeRaCON experiment and, along with K.W., was responsible for its implementation. X.C. and P.B.R. were responsible for the conception and design of this particular study project. P.B.R. planned and K.W. orchestrated all measurements. X.C. and K.W. compiled other data. X.C. analysed the data and wrote the first draft of the paper. X.C., K.S.R., H.Y.H.C., L.Z. and P.B.R. contributed to the review and editing of the paper. P.B.R. supervised the work. All authors approved the final article.

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Correspondence to
Peter B. Reich.

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Nature Climate Change thanks Baig Abdullah Al Shoumik, Jian Song and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.

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Extended data

Extended Data Fig. 1 Three-way interaction effect of CO2 enrichment, N addition and experimental year on belowground C stocks change rate (n = 48 plots; three plots per treatment combination).

Points show model-estimated means; error bars indicate 95% confidence intervals. The difference between groups was significant if 95% CIs of their coefficients did not overlap the other’s mean. The Namb and Nenrich represent ambient N and added N, while Camb and Cenrich represent ambient and elevated CO2. Experimental year was analyzed as a continuous variable but illustrated here based on the meaningful three levels of breakpoints (2012, 2017, 2022). The significance (P) is reported for each term tested, with P values calculated using a two-sided F test.

Extended Data Fig. 2 Total belowground C allocation (TBCA) in relation to root biomass C stock and aboveground biomass C stock when considered together.

a) root biomass C stock; b) aboveground biomass C stock. The black line and grey shaded areas represent the fitted regression and its bootstrapped 95% confidence intervals. The significance (P) is reported for each term tested, with P values calculated using a two-sided F test.

Extended Data Fig. 3 Total belowground C allocation (TBCA) in relation to community functional composition.

a) community-weighted mean of plant height (CWMHeight); b) community-weighted mean of leaf N content (CWMLeafN); c) community-weighted mean of root N content (CWMRootN). Black line shows the fitted mean relationship; grey shaded band indicates the 95% confidence interval around the fitted mean. The significance (P) is reported for each term tested, with P values calculated using a two-sided F test.

Extended Data Fig. 4 Total belowground C allocation (TBCA) in relation to soil carbon stock at different soil depths.

a) 0 – 20 cm; b) 20 – 40 cm; c) 40 – 60 cm. Black line shows the fitted mean relationship; grey shaded band indicates the 95% confidence interval around the fitted mean. The significance (P) is reported for each term tested, with P values calculated using a two-sided F test.

Extended Data Fig. 5 Total belowground C allocation (TBCA) in relation to soil N mineralization processes.

a) net soil N mineralization; b) net soil ammonification; c) net soil nitrification. Black line shows the fitted mean relationship; grey shaded band indicates the 95% confidence interval around the fitted mean. The significance (P) is reported for each term tested, with P values calculated using a two-sided F test.

Extended Data Fig. 6 Two-way interaction effect of warming and total belowground C allocation (TBCA) on net soil N mineralization.

Black and grey lines show the fitted mean relationship for each warming treatment, and grey shaded bands indicate the 95% confidence interval around the fitted mean. The significance (P) is reported for each term tested, with P values calculated using a two-sided F test. The Tamb and Telv represent ambient temperature and elevated temperature.

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Chen, X., Chen, H.Y.H., Rocci, K.S. et al. Long-term multiple global change interactions amplify belowground carbon allocation.
Nat. Clim. Chang. (2026). https://doi.org/10.1038/s41558-026-02678-x

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