Nitrogen input alleviates the priming effect of biochar addition on soil organic carbon decomposition

The combination of biochar and nitrogen (N) addition has been proposed as a potential strategy to mitigate climate change by sequestering carbon (C), while simultaneously boosting crop yields. However, our current knowledge about how biochar and N addition alter mineralization of native soil organic C, which is referred to priming effects (PEs), is largely limited. To address these uncertainties, three C3 biochar (pyrolyzing rice straw at 300, 550, and 800 ℃) and its combination with N fertilizer (urea) were incubated in a C4-derived soils at 25 ℃ in the laboratory. Our results showed that all these 3 types of biochar with different addition rate caused positive priming of native soil organic C decomposition (up to +58.4%), but negative or no priming occurred in biochar bound N treatments. The maximum negative PEs (-14.5%) were observed in 300 ℃ biochar with 1% addition rate bound N (B1300N) treatment. We find a negative correlation between the priming intensity and soil inorganic N content across all treatments. Furthermore, the biochar-induced PEs regulated by microbial biomass, fungi/bacteria ratio, and microbial metabolic efficiency. These findings indicated that eligible biochar used for blending traditional mineral fertilizer has a larger climate-change mitigation potential than biochar and fertilizer alone, while sustain relatively high crop yields.