This study meta-analyzes the decomposition and priming effects of biochar in soil, using data from 128 observations of biochar-derived CO₂ from 24 studies with stable and radioactive carbon isotopes. The results show that biochar decomposition increases logarithmically with time, with decomposition rates decreasing over time. The mean residence time (MRT) of labile and recalcitrant biochar C pools were estimated to be about 108 days and 556 years, respectively. These results indicate that only a small part of biochar is bioavailable, while the remaining 97% contributes to long-term carbon sequestration in soil. The study also evaluates the priming effect of biochar addition on soil organic matter (SOM) mineralization. Biochar slightly retarded SOM mineralization, with an overall mean of -3.8% (95% CI = -8.1-0.8%). Significant negative priming was observed in studies with short durations, crop-derived biochar, fast pyrolysis, low pyrolysis temperatures, and small application amounts. In contrast, biochar addition to sandy soils strongly stimulated SOM mineralization by 20.8%. This suggests that biochar stimulates microbial activity, especially in soils with low fertility. The study discusses abiotic and biotic processes affecting biochar decomposition, including pyrolysis temperature, soil clay content, and biochar characteristics. It concludes that biochar can persist in soils on a centennial scale and has a positive effect on SOM dynamics and thus on carbon sequestration. The study highlights the importance of biochar as a carbon sink and its potential to mitigate climate change through long-term carbon sequestration in soils. The findings suggest that biochar application can enhance soil carbon storage, improve soil fertility, and reduce greenhouse gas emissions. The study also notes that biochar application can have indirect effects on carbon sequestration by reducing SOM decomposition rates and increasing plant biomass input. Overall, the study provides a comprehensive understanding of biochar stability in soil and its implications for carbon sequestration.This study meta-analyzes the decomposition and priming effects of biochar in soil, using data from 128 observations of biochar-derived CO₂ from 24 studies with stable and radioactive carbon isotopes. The results show that biochar decomposition increases logarithmically with time, with decomposition rates decreasing over time. The mean residence time (MRT) of labile and recalcitrant biochar C pools were estimated to be about 108 days and 556 years, respectively. These results indicate that only a small part of biochar is bioavailable, while the remaining 97% contributes to long-term carbon sequestration in soil. The study also evaluates the priming effect of biochar addition on soil organic matter (SOM) mineralization. Biochar slightly retarded SOM mineralization, with an overall mean of -3.8% (95% CI = -8.1-0.8%). Significant negative priming was observed in studies with short durations, crop-derived biochar, fast pyrolysis, low pyrolysis temperatures, and small application amounts. In contrast, biochar addition to sandy soils strongly stimulated SOM mineralization by 20.8%. This suggests that biochar stimulates microbial activity, especially in soils with low fertility. The study discusses abiotic and biotic processes affecting biochar decomposition, including pyrolysis temperature, soil clay content, and biochar characteristics. It concludes that biochar can persist in soils on a centennial scale and has a positive effect on SOM dynamics and thus on carbon sequestration. The study highlights the importance of biochar as a carbon sink and its potential to mitigate climate change through long-term carbon sequestration in soils. The findings suggest that biochar application can enhance soil carbon storage, improve soil fertility, and reduce greenhouse gas emissions. The study also notes that biochar application can have indirect effects on carbon sequestration by reducing SOM decomposition rates and increasing plant biomass input. Overall, the study provides a comprehensive understanding of biochar stability in soil and its implications for carbon sequestration.