Investigating the biochar effects on C-mineralization and sequestration of carbon in soil compared with conventional amendments using the stable isotope (δ13C) approach

Biomass-derived black carbon (biochar) is considered to be an effective tool to mitigate global warming by long-term C-sequestration in soil and to influence C-mineralization via priming effects. However, the underlying mechanism of biochar (BC) priming relative to conventional biowaste (BW) amendments remains uncertain. Here, we used a stable carbon isotope (delta C-13) approach to estimate the possible biochar effects on native soil C-mineralization compared with various BW additions and potential carbon sequestration. The results show that immediately after application, BC suppresses and then increases C-mineralization, causing a loss of 0.14-7.17 mg-CO2-C g(-1)-C compared to the control (0.24-1.86 mg-CO2-C g(-1)-C) over 1-120 days. Negative priming was observed for BC compared to various BW amendments (-10.22 to -23.56 mg-CO2-C g(-1)-soil-C); however, it was trivially positive relative to that of the control (8.64 mg-CO2-C g(-1)-soil-C). Furthermore, according to the residual carbon and delta C-13 signature of postexperimental soil carbon, BC-C significantly increased (P < 0.05) the soil carbon stock by carbon sequestration in soil compared with various biowaste amendments. The results of cumulative CO2-C emissions, relative priming effects, and carbon storage indicate that BC reduces C-mineralization, resulting in greater C-sequestration compared with other BW amendments, and the magnitude of this effect initially increases and then decreases and stabilizes over time, possibly due to the presence of recalcitrant-C (4.92 mg-C g(-1)-soil) in BC, the reduced microbial activity, and the sorption of labile organic carbon (OC) onto BC particles.