Soil carbon persistence governed by plant input and mineral protection: evidence from soil radiocarbon

Abstract:

Elucidating the processes underlying the persistence of soil organic matter (SOM) over decadal to millennial timescales is the prerequisite for accurately projecting the soil carbon feedback to climate change. Though multiple abiotic processes (i.e., climatic stabilization, mineral-organic association and selective preservation) have been proposed to explain the persistence of SOM, the role of biotic process (i.e., plant carbon input) and its interplay with these abiotic processes in different soil layers have not been evaluated over broad geographic scale. Here, based on the multiple-layer soil radiocarbon (△¹⁴C), molecular SOM composition and clay mineral measurements across the Tibetan Plateau and a global-scale △¹⁴C synthesis, we explored the relative importance of plant carbon input in relation to climatic stabilization, mineral protection and selective preservation in regulating SOM persistence. Partial correlation analysis and structure equation modelling consistently revealed that the key process underlying soil △¹⁴C variations was strongly depth-dependent on the Tibetan Plateau. Plant carbon input was the major process that positively drove the △¹⁴C variations in topsoil, whereas mineral protection by iron-aluminum oxides and cations exerted a more important role in the subsoil. The predominant roles of plant carbon input and organo-mineral association in governing surface and deep soil carbon persistence were further confirmed by the global-scale synthesis. These findings provide a continentally evidence for the destabilization of soil organic matter by plant carbon input, and highlight the need to consider depth-associated plant-soil-mineral interactions in Earth system models to improve the predictions of long-term soil carbon dynamics.