negative relationship between the IC/TC and the soil pH values was observed
(Fig. 1b). All biochar-amended soils showed higher IC/TC ratios
compared to the control in the acidic soils (with the highest IC/TC
ratio 61.5%, 32.5%, and 11.9% for S1, S2, and S3, respectively at early
stage of the incubation). In addition, the highest mineralization rate of
biochar appeared on the first day for soils S1 and S2, following an
order of 700BC N 500BC N 300BC. Moreover, the mineralization of
700BC on the first day in soils S1 and S2 were almost the same, occupying
65% and 59% of the total CO2 emission. The transient peak of degradation
rate from biochar in soils S1 and S2 on the first day with 500BC
and 700BC followed by a sharp decline indicated that a faster abiotic release
of carbonates from biochar with lower pH (Fig. S2). The effect of
abiotic release of carbonates in biochar for acid soils only occurs sharply
in the early stage of incubation, based on the content of carbonates in
biochar. Although more carbonates in the biochar generated at higher
temperature, CO2 release from inorganic carbon was observed to be
higher in 500BC than 700BC in acidic soils, mainly due to the higher
soil pH induced by 700BC.