Natural fire-derived charcoal resembles high-temperature biochar in regulating soil CO2 emissions from a subtropical plantation soil

Char is a carbon (C)-rich pyrogenic material generated either during natural fire events (natural charcoal) or through the thermochemical conversion of plant biomass (engineered biochar). However, whether these two types of char have comparable effects on soil CO 2 emissions remains unclear. In this study, we conducted a 30-day incubation experiment to compare the effects of charcoal produced from Pinus massoniana bark during broadcast burning and engineered biochars produced from the same feedstock at 300, 500, and 900 °C (B300, B500, and B900) on soil CO 2 emissions, physicochemical properties, and bacterial diversity and composition. The addition of B300 significantly increased soil CO 2 emissions ( p < 0.05), whereas B500, B900, and charcoal had no significant effects. B300 addition markedly increased the relative abundances of Proteobacteria and Cyanobacteria while decreasing those of Acidobacteriota, Chloroflexi, and Verrucomicrobiota ( p < 0.001). Mixed-effects models accounting for treatment variation showed that soil pH was negatively associated with cumulative CO 2 emissions, whereas Proteobacteria exhibited a positive association. Random forest analysis identified Proteobacteria and Acidobacteriota as potential predictors of cumulative CO 2 emissions, although these relationships require further validation. In contrast, natural fire-derived charcoal caused minimal changes in bacterial community composition. Overall, our findings demonstrate that high-temperature biochars (>500 °C) exhibit similar effects on soil CO 2 emissions and bacterial community to natural charcoal in subtropical plantation soils, highlighting their potential as functional analogues of fire-derived charcoal.