Effects of biochar on carbon mineralization of coastal wetland soils in the Yellow River Delta, China

• Effects of biochar on SOC mineralization in a coastal wetland soil was studied.
• Peanut shell biochar addition to the soil enhanced carbon sequestration.
• Biochar addition facilitated the formation of carbonates.
• Biochar addition decreased microbial biomass carbon and microbial quotient.

Biochar (BC) application for improving soil quality and carbon sequestration has generated great interest for scientists and policy makers. BC can influence soil organic carbon (SOC) mineralization through priming effects. Positive, negative or no priming effects on C mineralization has been observed following BC additions to soils. However, uncertainty still remains about the influence of biochar on SOC mineralization in the coastal wetland soils of the Yellow River Delta, China. Therefore, a five months of incubation experiment using the coastal wetland soil was conducted to investigate the effects of adding BC produced from peanut shell at 350 °C on SOC mineralization at the rates of 0% (0%BC), 0.1% (0.1%BC), 1% (1%BC) and 3% (3%BC) (w/w). BC addition increased the cumulative CO2 emissions, indicating that the cumulative SOC mineralization was enhanced in the coastal soil by BC application. However, the increased C mineralized only accounted for 1.71%, 0.32% and 0.17% of the BC-C added in the 0.1%BC, 1%BC and 3%BC treatments, respectively. Moreover, the experimental values of SOC mineralization was much lower than that of the theoretical values in both 1%BC and 3%BC treatments, indicating that a negative priming effect occurred. This may be explained by two reasons: (1) the conversion process of SOC to dissolved inorganic C (DIC) was accelerated by BC addition, which was confirmed by SEM image; (2) the amounts of available C substrate and microorganisms decreased via the sorption of labile organic C (LOC) and microorganisms onto BC. These results suggest that BC application will enhance soil C storage in the salinized wetland soils.