2.4. Carbon mineralization source and priming effects
100 μl gas samples were withdrawn from the incubated soils and
soil-biochar mixture vials to the sample bridge for δ13C analysis using
Precon-IRMS (Delta V Thermo Finnigan). The amount of biochar mineralized
(CB) from biochar-amended soil was calculated as:
CB ¼
CT δT
13CO2−δS
13CO2
δB
13CO2−δS
13CO2
ð1Þ
where CT is the total C mineralized from the biochar-amended soil,
δT
13CO2 is the δT
13C value of the CO2-C evolved from the biochar-amended
soils, δS
13CO2 is the δT
13C value of CO2-C evolved from the control soil, and
δS
13CO2 is the initial δT
13C value of the biochar. The amount of the soil-C
mineralized (CS,B) from the biochar-amended soil and the priming effects
(PE) induced by the biochar on mineralization of the native organic
carbon in the soils were calculated as:
CS;B ¼ CT−CB ð2Þ
PE ¼ CS;B−CS ð3Þ
where CS is the amount of CO2-C evolved from the control soil, CT is the
total C mineralized from the biochar-amended soil, CB is the amount of C
mineralized from biochar. The positive priming effect means accelerating
of SOC mineralization by biochar. In contrast, negative priming effect
means the suppression of SOC mineralization by biochar.
Cumulative biochar degradation was calculated. Furthermore, to
eliminate the impact of soil SOC content on biochar degradation, the
mineralization rate of biochar as per unit native SOC were used to
describe the degradation of biochar in different soils.