Résumé
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 a parts per thousand 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.