Priming by Black Carbon Increases Rather Than Decreases Non-Pyrogenic Soil Organic Carbon in the Long Term.

Observed increases in the mineralisation rate of labile organic carbon (LOC) in the presence of black carbon (BC) have led to speculation that corresponding decreases in non-pyrogenic (non-BC) soil organic carbon (npSOC) could significantly reduce or negate the C sequestration benefit of BC in soils. The range of potential long-term impacts of priming by BC on npSOC stocks were investigated using a version of the RothC soil carbon model, modified to include priming interactions with BC, and coupled to a crop-production and to a BC production/decomposition model.  Here we show that the potential effect of an increased LOC decomposition-rate on long-term npSOC stocks is negligible, potentially causing no more than 3-4% loss of npSOC over 100 yr if 50% of above-ground crop residues were converted to BC annually. Conversely, if the BC-stimulated enhanced-stabilization of npSOC that has been observed in laboratory trials is extrapolated to the long-term, it would greatly increase npSOC by 30-60%.