Abstract
As one of the most durable legacies of fire, charcoal plays a key role in long-term soil carbon (C) storage due to its long residence time. However, few attempts have been made to investigate the impact of naturally deposited charcoal on soil organic C (SOC) stability in fire-affected forests in a long-term field trial. In this study, we used a field-based charcoal manipulation experiment to assess the input of charcoal on post-fire SOC stability in a subtropical plantation forest. The experimental design included four treatments: removal of all visible charcoal (C0), charcoal retained in-situ (C1), addition of charcoal removed from C0 plots to separate plots (C2), and an unburnt control (UB). Seven years after treatment implementation, soil samples were collected from 0 to 10 and 10–20 cm depth to measure soil organic C fractions, microbial biomass C (MBC), C pool management index (CPMI), aggregate stability and the distribution of organic C within aggregate size classes. Our results showed that charcoal had no significant effect on dissolved organic C (DOC) at either depth. However, charcoal significantly influenced MBC, CPMI, and the distribution of SOC in small aggregate fractions (<0.05 mm) in a depth-dependent manner. At the 0–10 cm depth, CPMI and the allocation of SOC to small aggregates were significantly higher in C2 and UB soils than in C0 (p < 0.05), whereas no differences were observed at the 10–20 cm depth. In contrast, MBC was significantly higher in C2 and UB than in C0 soils only at the 10–20 cm depth (p < 0.05). Despite the persistence of negative effects from the initial burning event, our findings suggest that fire-derived charcoal can enhance SOC stability by promoting microbial assimilation and facilitating SOC allocation to more stable aggregate fractions with longer turnover times. Taken together, these findings suggest that charcoal deposited during fire contributes to soil C stabilization in subtropical forest plantations subjected to broadcast burning.
•Negative impact of broadcast burning on SOC persists seven years later.•Charcoal enhances post-fire recovery of soil MBC and the MBC/SOC ratio.•Charcoal increases the allocation of organic C in finer soil fractions.•Charcoal enhances post-fire recovery of C pool management index.•Charcoal plays a positive role in post-fire soil C stabilization.