Biochar built soil carbon over a decade by stabilizing rhizodeposits


Biochar can increase the stable C content of soil. However, studies on the longer-term role of plant–soil–biochar interactions and the consequent changes to native soil organic carbon (SOC) are lacking. Periodic 13CO2 pulse labelling of ryegrass was used to monitor belowground C allocation, SOC priming, and stabilization of root-derived C for a 15-month period—commencing 8.2 years after biochar (Eucalyptus saligna, 550 °C) was amended into a subtropical ferralsol. We found that field-aged biochar enhanced the belowground recovery of new root-derived C (13C) by 20%, and facilitated negative rhizosphere priming (it slowed SOC mineralization by 5.5%, that is, 46 g CO2-C m−2 yr−1). Retention of root-derived 13C in the stable organo-mineral fraction (<53 μm) was also increased (6%, P < 0.05). Through synchrotron-based spectroscopic analysis of bulk soil, field-aged biochar and microaggregates (<250 μm), we demonstrate that biochar accelerates the formation of microaggregates via organo-mineral interactions, resulting in the stabilization and accumulation of SOC in a rhodic ferralsol.

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Figure 1: Proposed mechanisms for positive rhizosphere priming of soil organic carbon (SOC) counteracted by biochar-induced negative priming and stabilization of rhizodeposits (new C) in a ferralsol after 9.5 years.
Figure 2: Change in rhizosphere priming of soil organic carbon (SOC) between 8.2 and 9.5 years post biochar addition.
Figure 3: Change in total soil C stocks and root biomass C in the unamended control and field-aged biochar-amended plots.
Figure 4: Spectroscopic analysis of bulk planted soils in the unamended control and field-aged biochar-amended plots.


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The authors thank the Australian Government, Department of Agriculture and Water Resources for supporting the National Biochar Initiatives (2009–2012, 2012–2014) which co-funded this research. We are particularly grateful to P. Slavich, as one of the key founders of this long-term field experiment, for providing insightful comments on the initial draft. Part of this research was undertaken on the soft X-ray spectroscopy beamline at the Australian Synchrotron, Victoria, Australia (grant number AS151_SXR_9599). We thank the chief beamline scientist, B. Cowie, for his technical support on the soft X-ray analysis. We also appreciate the technical support from S. Petty and J. Rust for maintaining this field experiment over the past decade, and laboratory support from N. Morris. We also thank C. Achete from INMETRO, Brazil and B. Gong from the University of New South Wales, Australia, for performing XPS analysis of biochars and soils, respectively. We acknowledge the intellectual contribution from S. Donne for discussions on the potential mechanisms of biochar-induced stabilization of rhizodeposits. We also thank Y. Fang for giving advice and reviewing 13C calculations.

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Z.W. drafted and wrote the manuscript, carried out experimental design, setup and conducted experiments, data collection and analysis; L.V.Z. and B.P.S. wrote the manuscript, aided in experimental design and provided critical revision of the article; E.T. aided in experimental design, data collection and analysis, and provided critical revision of the article; S.J. and M.T.R. collected and analysed data, and provided critical revision of the article; L.M.M. wrote the manuscript, and provided critical revision of the article; T.J.R. and S.W.L.K. provided critical revision of the article; S.M. and D.C. analysed data and provided critical revision of the article; J.R.A. analysed data; B.S.A. and A.C. provided critical revision of the article. All authors provided final approval of the revision to be published.

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Correspondence to Lukas Van Zwieten.

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(Han) Weng, Z., Van Zwieten, L., Singh, B. et al. Biochar built soil carbon over a decade by stabilizing rhizodeposits. Nature Clim Change 7, 371–376 (2017).

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