Increase in Recalcitrant Carbon: a Positive Balance between Stabilization and Priming Effect

Abstract:

Recalcitrant carbon (C) stored in soils plays a critical role in regulating climate change because of its huge amount and relatively low turnover rate. Positive priming effect by increased labile C inputs could lead to more recalcitrant C release to the atmosphere. However, the stabilization of the newly added labile C has received much less attention. As a result, the quantitative balance between the stabilization and priming and consequently changes in recalcitrant C are still unclear. In this study, incubation data of different soils (i.e., forest, grassland, cropland, and vertisol) with isotope-labeled labile substrate additions were collected. An alternative version of the Introductory Carbon Balance Model (ICBM) with stabilization and positive priming effect was used to simulate the C dynamics during the incubation and then run forward for ten years. The results showed that at the end of incubation, an equivalent of 5.45 – 26.1% of added C was primed from the original SOM for the four soils. Meanwhile, 40.9 – 70.7% of added C was stabilized, leading to a net increase in recalcitrant C by an equivalent of 18.0 – 50.0% of added C. After running model for ten years, the recalcitrant C was greater with than without initial labile C addition by an equivalent of 33.0, 2.01, 21.6, and 0.62% of added C for the forest, grassland, cropland and vertisol, respectively. Our results suggest that stabilization overcompensates the C loss induced by positive priming effect, indicating that stimulated labile C input under CO₂ enrichment may increase the recalcitrant C storage in soils, and consequently dampen the further increase in atmospheric CO₂ concentrations and climate change. The results also suggest that both stabilization and positive priming effect may vary among ecosystems and with the type and amount of added substrates. To better quantify the net change in recalcitrant C and thus long-term soil C storage, comprehensive studies on the effects of soil type, added substrate type and amount on stabilization and priming effect are critically needed.