A test of the hierarchical model of litter decomposition

Abstract

Our basic understanding of plant litter decomposition informs the assumptions underlying widely applied soil biogeochemical models, including those embedded in Earth system models. Confidence in projected carbon cycle–climate feedbacks therefore depends on accurate knowledge about the controls regulating the rate at which plant biomass is decomposed into products such as CO2. Here we test underlying assumptions of the dominant conceptual model of litter decomposition. The model posits that a primary control on the rate of decomposition at regional to global scales is climate (temperature and moisture), with the controlling effects of decomposers negligible at such broad spatial scales. Using a regional-scale litter decomposition experiment at six sites spanning from northern Sweden to southern France—and capturing both within and among site variation in putative controls—we find that contrary to predictions from the hierarchical model, decomposer (microbial) biomass strongly regulates decomposition at regional scales. Furthermore, the size of the microbial biomass dictates the absolute change in decomposition rates with changing climate variables. Our findings suggest the need for revision of the hierarchical model, with decomposers acting as both local- and broad-scale controls on litter decomposition rates, necessitating their explicit consideration in global biogeochemical models.

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Fig. 1: Study design and site characteristics.
Fig. 2: Competing assumptions for how decomposer communities affect relationships between climate and decomposition rates at regional to global scales.
Fig. 3: Measured variation in decomposition rates and controlling variables within and among sites.
Fig. 4: Estimated effects of temperature and moisture controls on decomposition rates.
Fig. 5: Estimated effects of controls on decomposition rates.

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Acknowledgements

We thank R. Pas and M. Hundscheid for lab assistance, and the Röbäcksdalen field station staff for providing land and logistic support at the Umeå site. Research was supported by grants to M.A.B. from the US National Science Foundation (DEB-1457614), The Royal Netherlands Academy of Arts and Sciences (Visiting Professors Programme), and the Netherlands Production Ecology & Resource Conservation Programme for Visiting Scientists. G.F.V. was supported by an NWO-VENI from the Netherlands Organisation for Scientific Research (863.14.013). M.M.-F. and W.H.v.d.P. were supported by a European Research Council grant (ERC-Adv 260-55290), and G.T.F. by grant EC2CO-Multivers. We thank the Bradford lab group for comments on an earlier version of the manuscript.

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M.A.B. and G.F.V. designed the study, co-wrote the manuscript, constructed litterbags and carried out the lab analyses. All authors established, maintained and collected data from the field sites. M.A.B., G.F.V., D.S.M. and S.A.W. analysed data. All authors contributed to data interpretation and writing of the paper.

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Correspondence to Mark A. Bradford.

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Bradford, M.A., Veen, G.F.(., Bonis, A. et al. A test of the hierarchical model of litter decomposition. Nat Ecol Evol 1, 1836–1845 (2017). https://doi.org/10.1038/s41559-017-0367-4

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