Quantifying and isolating stable soil organic carbon using long-term bare fallow experiments

P. Barré, T. Eglin, B. T. Christensen, P. Ciais, S. Houot, T. Kätterer, F. van Oort, P. Peylin, P. R. Poulton, V. Romanenkov, C. Chenu
2010 Biogeosciences  
The stability of soil organic matter (SOM) is a major source of uncertainty in predicting atmospheric CO 2 concentration during the 21st century. Isolating the stable soil carbon (C) from other, more labile, C fractions in soil is of prime importance for calibrating soil C simulation models, and gaining insights into the mechanisms that lead to soil C stability. Long-term experiments with continuous bare fallow (vegetation-free) treatments in which the decay of soil C is monitored for decades
more » ... tored for decades after all inputs of C have stopped, provide a unique opportunity to assess the quantity of stable soil C. We analyzed data from six bare fallow experiments of long-duration (>30 yrs), covering a range of soil types and climate conditions, and sited at Askov (Denmark), Grignon and Versailles (France), Kursk (Russia), Rothamsted (UK), and Ultuna (Sweden). A conceptual three pool model dividing soil C into a labile pool (turnover time of a several years), an intermediate pool (turnover time of a several decades) and a stable pool (turnover time of a several centuries or more) fits well with the long term C decline observed in the bare fallow soils. The estimate of stable C ranged from 2.7 g C kg −1 at Rothamsted to 6.8 g C kg −1 at Grignon. The uncertainty Correspondence to: P. Barré (barre@geologie.ens.fr) associated with estimates of the stable pool was large due to the short duration of the fallow treatments relative to the turnover time of stable soil C. At Versailles, where there is least uncertainty associated with the determination of a stable pool, the soil contains predominantly stable C after 80 years of continuous bare fallow. Such a site represents a unique research platform for characterization of the nature of stable SOM and its vulnerability to global change. the rate at which native SOM decomposes (Johnston et al., 2009). However, soil C dynamics are still discussed from the point of view of their sensitivity to climate and ecosystem productivity changes (Heimann and Reichstein, 2008) . This has lead to a wide range in the global model predictions of future soil C storage (Friedlingstein et al., 2006; Sitch et al.,
doi:10.5194/bg-7-3839-2010 fatcat:yo2mm4m3wveftbk6rchc6cvz5e