Observation-constrained prediction of the response of whole soil profile carbon to warming across the globe

Mr Zhongkui Luo1

1CSIRO Agriculture and Food, Canberra, Australia

The response of global soil organic carbon (SOC) stock to warming regulates carbon cycle-climate feedbacks. Although SOC in topsoils above 0.3 m has been comprehensively studied, the response of SOC in the whole soil profile to warming has never been explicitly quantified at the global scale. Here we combine mechanistic soil profile carbon models constrained by global observational databases with machine learning techniques to predict the response of whole soil profile SOC (down to 2 m) to warming across the globe at 1 km resolution. The results demonstrate that the negative effect of warming on SOC extends to deeper soil layers over the world. Under 2° warming assuming no carbon input change, the model predicts a 6% (equivalent to 123.6 Pg C) decrease in global SOC stock in the 0–2 m soil layer, to which the 0–0.2, 0.2–1 and 1–2 m soil layers contribute 23.5%, 38.1% and 38.4%, respectively. To offset this decrease, a 6.8% increase of carbon input is required. Furthermore, we find that downward movement of SOC along the soil profile and the priming of old carbon decomposition by new carbon can increase the resilience of SOC to warming. Under a scenario of no priming effect and downward movement, the predicted decrease of SOC stock under 2° warming without carbon input change is increased to 17.6%, while the carbon input required to offset this larger SOC decrease is shifted up to 21.6%. This study provides the first estimation of whole soil profile SOC change under warming across the globe, and suggests that the priming effect and downward movement of SOC moderate the sensitivity of SOC stock to warming although additional carbon input is a prerequisite to offset the negative effect of warming on SOC stock.

Biography: Bio to come

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