Abstract
The universally observed exponential increase in soil-surface CO2 efflux (‘soil respiration’; FS) with increasing temperature has led to speculation that global warming will accelerate soil-organic-carbon (SOC) decomposition1, reduce SOC storage, and drive a positive feedback to future warming2. However, interpreting temperature–FS relationships, and so modelling terrestrial carbon balance in a warmer world, is complicated by the many sources of respired carbon that contribute to FS (ref. 3) and a poor understanding of how temperature influences SOC decomposition rates4. Here we quantified FS, litterfall, bulk SOC and SOC fraction size and turnover, and total below-ground carbon flux (TBCF) across a highly constrained 5.2 °C mean annual temperature (MAT) gradient in tropical montane wet forest5. From these, we determined that: increases in TBCF and litterfall explain >90% of the increase in FS with MAT; bulk SOC and SOC fraction size and turnover rate do not vary with MAT; and increases in TBCF and litterfall do not influence SOC storage or turnover on century to millennial timescales. This gradient study shows that for tropical montane wet forest, long-term and whole-ecosystem warming accelerates below-ground carbon processes with no apparent impact on SOC storage.
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Acknowledgements
We thank M. Long, J. Albano, M. Koontz, R. Mosley, J. Johansen, B. Hwang, K. Kinney and K. Kaneshiro for assistance with data collection, C. Fissore for assembling previously published radiocarbon data, T. Giambelluca for assistance with climate analyses, and D. Binkley, M. Busse, P. Selmants and D. Levinson for reviews of earlier versions of the manuscript. We thank the National Science Foundation (C.M.L. and C.P.G.), the College of Tropical Agriculture and Human Resources at the University of Hawaii at Manoa (C.M.L.), the Pacific Southwest Research Station, USDA Forest Service (C.P.G), and the Carnegie Institution for Science (G.P.A.) for funding to establish the study, collect flux data, and process and analyse soil samples. We thank C. Swanston and K. Heckman of the Northern Research Station, USDA Forest Service for funding, preparation and bulk SOC radiocarbon analyses at Lawrence Livermore National Laboratory; P. Reimer and the 14CHRONO Centre for Climate, the Environment, and Chronology, Queen’s University Belfast for radiocarbon analyses of SOC fractions; the USDA Forest Service, the State of Hawaii Department of Land and Natural Resources, Division of Forestry and Wildlife and the Parker Ranch for access to research plots in the Hawaii Experimental Tropical Forest; the US Fish and Wildlife Service for access to plots in Hakalau Forest National Wildlife Refuge. The Carnegie Airborne Observatory is made possible by the Andrew Mellon Foundation, John D. and Catherine T. MacArthur Foundation, Avatar Alliance Foundation, Grantham Foundation for the Protection of the Environment, Mary Anne Nyburg Baker and G. Leonard Baker Jr., and William R. Hearst III.
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C.M.L. and C.P.G. designed the study and secured funding for flux and stock analyses; C.P.G. secured funding for bulk SOC radiocarbon analyses; S.E.C. secured funding for fraction SOC radiocarbon analyses SRO data collection and analyses; G.P.A. secured funding for LiDAR data collection and analyses; all authors contributed to data interpretation and manuscript preparation; C.M.L. and C.P.G. led collection of flux and stock data; S.E.C. led analysis and interpretation of radiocarbon measurements; S.E.C. led collection, analysis and interpretation of SRO data; G.P.A. led LiDAR-based analyses of forest plots and, with the other authors, plot selection; C.M.L., C.P.G. and S.E.C. drafted figures; C.P.G. wrote the initial draft of the manuscript; all authors discussed and interpreted results, and provided editorial input.
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Giardina, C., Litton, C., Crow, S. et al. Warming-related increases in soil CO2 efflux are explained by increased below-ground carbon flux. Nature Clim Change 4, 822–827 (2014). https://doi.org/10.1038/nclimate2322
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DOI: https://doi.org/10.1038/nclimate2322
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