Subtropical giant podzol chronosequence reveals that soil carbon stabilisation is not governed by litter quality
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The magnitude of the carbon flux between soil and atmosphere has prompted efforts to better understand the controls over the fate of carbon in plant litter that re-enters the atmosphere as carbon dioxide or is sequestered as soil organic carbon (SOC). It remains unresolved if the long-term fate of litter carbon is driven by biochemical properties of litter or by soil properties that reduce the ability of soil organisms to decompose litter-derived carbon. The prominent role that reactive soil minerals play in stabilising SOC have hindered investigation into the single role of litter quality on long-term SOC stability. Here we investigated the independent effects of litter quality on soil carbon stabilisation across a 460,000 year sand dune chronosequence characterised by a pronounced nutrient and litter quality gradient with minimum presence of interfering soil minerals. Using a steady state turnover model to interpret radiocarbon activity in soils collected ≈40 years apart, we show that the turnover time of SOC in the A horizon averaged 22 years (ranging from 16 to 27 years) across the chronosequence. This finding strongly contrasts other chronosequences where SOC turnover rates range from 60 to 726 years in concert with changing abundance and composition of soil minerals. Our study demonstrates that the long-term stability of SOC in surface horizons may be largely determined by interaction with soil minerals and that litter quality per se does not govern carbon stabilisation.
KeywordsSoil carbon Turnover Litter quality Chronosequence Soil nutrients Radiocarbon
We thank Shelby Fangrath, Stéphane Guillou and Mark Bonner for assistance in the field, Justin McCoombes for assistance with laboratory work, and Thomas Orton helping with statistical analysis. We thank Jeff Baldock and two anonymous reviewers for their constructive comments on the draft manuscript. The authors are grateful for the financial assistance from the Australian Institute Nuclear of Nuclear Science and Engineering Ltd. (AINSE) that enabled Δ14C analysis on the Accelerator Mass Spectrometer.
Conflict of interest
The authors declare that they have no conflict of interest.
The study was partly funded by an AINSE Grant (12/038) to SS and ARJ.
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