Interactive carbon priming, microbial response and biochar persistence in a Vertisol with varied inputs of biochar and labile organic matter

There has been great interest in biochar application to soil for long-term carbon (C) sequestration. However, the interactive priming of organic C mineralization, including shifts in microbial community structure and the persistence of biochar in a clayey soil amended with biochar and labile organic matter (LOM) over a relatively long period (i.e. years) remain poorly understood. A 2-year incubation study was carried out with δ 13 C-depleted biochars produced from Eucalyptus saligna Sm. wood biomass at 450 and 550°C. Each of the biochars (at 2%, w/w) in combination with LOM, such as sugarcane residue at input rates of 0, 1, 2 or 4% w/w, were mixed with a C 4 -dominated Vertisol. The interactive effect of biochar and LOM on the structure of the microbial community was analysed by terminal restriction fragment length polymorphism (T-RFLP). Our results showed that at the small LOM rates (0 and 1%), there was a positive priming effect of biochar on organic C in soil (i.e. native soil organic C (SOC) + LOM-C)), which shifted to being negative when the LOM input was increased to 2 or 4%. Over the 2 years, mineralization of C from the 450°C biochar (1.2–1.7%) was significantly greater than that for 550°C biochar (0.6–1.0%), and the positively primed mineralization of biochar-C by LOM was enhanced by the increasing rates of LOM input. The negative priming of native SOC + LOM-C mineralization by biochar was greater at large than small inputs of LOM, which would have been facilitated by greater shifting in fungal communities, while enhancing biochar-C mineralization and possibly soil aggregation. In conclusion, over the long term, the amount of LOM stabilized by biochar was greater than that of positively primed biochar-C mineralization by LOM, in particular at the large LOM input. Biochar can persist in soil on a centennial scale and decreases the turnover of native SOC + LOM-C over the long term, whereas LOM input can shift microbial communities, favouring LOM stabilization in the biochar-amended Vertisol. Highlights: Do C priming, biochar persistence and microbial response change 2 years after biochar–LOM inputs? Examined interactive C priming (stable-C isotope), microbial community structure and biochar MRT. Priming of SOC ± LOM-C by biochar and vice-versa increased with LOM inputs. Biochar–LOM interaction (2-year) shifted microorganisms, favouring LOM-C stabilization in a Vertisol.