Disentangling residence time and temperature sensitivity of microbial decomposition in a global soil carbon model

[摘要] Recent studies have identified the first-order representation of microbialdecomposition as a major source of uncertainty in simulations andprojections of the terrestrial carbon balance. Here, we use a reducedcomplexity model representative of current state-of-the-art models of soilorganic carbon decomposition. We undertake a systematic sensitivity analysisto disentangle the effect of the time-invariant baseline residence time(k) and the sensitivity of microbial decomposition to temperature (Q₁₀) onsoil carbon dynamics at regional and global scales. Our simulations producea range in total soil carbon at equilibrium of ~ 592 to 2745 Pg C, which is similarto the ~ 561 to 2938 Pg C range inpre-industrial soil carbon in models used in the fifth phase of the CoupledModel Intercomparison Project (CMIP5). This range depends primarily on the value ofk, although the impact of Q₁₀ is not trivial at regional scales. Asclimate changes through the historical period, and into the future, k isprimarily responsible for the magnitude of the response in soil carbon,whereas Q₁₀ determines whether the soil remains a sink, or becomes asource in the future mostly by its effect on mid-latitude carbon balance.If we restrict our simulations to those simulating total soil carbon stocksconsistent with observations of current stocks, the projected range in totalsoil carbon change is reduced by 42% for the historical simulations and45% for the future projections. However, while this observation-basedselection dismisses outliers, it does not increase confidence in the futuresign of the soil carbon feedback. We conclude that despite this result,future estimates of soil carbon and how soil carbon responds to climatechange should be more constrained by available data sets of carbon stocks.

[学科分类] 地球化学与岩石