Priming, stabilization and temperature sensitivity of native SOC is controlled by microbial responses and physicochemical properties of biochar

Biochars generally result in short-term positive priming of native soil organic carbon (SOC), but longer-term carbon (C) stabilization, and these effects can be altered by global warming. However, uncertainty remains about the mechanisms associated with these priming effects, temperature sensitivity of native SOC, and microbial responses to biochars of differing properties. To address these knowledge gaps, rice straw biochars (produced at 300 and 800 °C at 2% w/w application rate), and their labile (water extracted) fraction and recalcitrant (chemically oxidized) fraction (obtained from the equivalent weight of biochar) were incubated in a C4 dominated soil at 15, 25, and 35 °C. Our results showed that 300 °C biochar and its recalcitrant fraction resulted in an increased SOC mineralization due to positive priming across the incubation thermosequence. This was likely linked to an observed increase in the abundance of K-strategists (fungi and Actinobacteria). The biochar produced at 800 °C and its recalcitrant fraction resulted in the stabilization of native SOC (i.e., negative priming) at all temperatures, likely due to the adsorptive protection of native SOC by the large surface area. The water extractable C from both biochars generally induced SOC stabilization across the thermosequence, which could be attributed to microbial shifts to r-strategists preferentially utilizing labile C components in biochar. Both biochars increased SOC stabilization with warming from 15 to 25 °C, supporting the role of biochar application in soil C sequestration in cooler regions. The lower SOC stabilization by biochars with temperature increases from 25 to 35 °C was correlated with the biochar-induced increases in fungal growth (K-strategist) under warming. The low-temperature biochar increased the abundance of aromatic C decomposers and concomitantly lowered the Q10 and activation energy (Ea) of native SOC. The findings from this study highlight that the low- and high-temperature biochars can result in various changes in native SOC mineralization, as well as temperature sensitivity, mainly by microbial population alterations and physicochemical interactions. •300 °C biochar and its recalcitrant fraction caused SOC loss at 15, 25 and 35 °C.•The SOC loss by 300 °C biochar was likely due to increased fungi and Actinobacteria.•800 °C biochar and its recalcitrant fraction stabilized SOC at 15, 25 and 35 °C.•Water extracts of biochar stabilized SOC, likely due to C substrate swi