Fire-deposited charcoal enhances soil microbial biomass in a recently harvested subtropical plantation forest

Charcoal, a byproduct of biomass burning, is widely and heterogeneously distributed in fire-affected ecosystems. However, few field studies have been conducted to evaluate the effects of fire-deposited charcoal on the post-fire soil quality. In this study, we aimed to investigate whether charcoal generated during post timber harvest broadcast burning influenced the recovery of individual soil properties and overall soil quality in subtropical forest plantations. Broadcast burning was conducted on experimental Pinus massoniana plantation timber harvest sites in southern China. Surface soils (0-10 cm) were collected in plots established on the burnt sites five years after the disturbance event. Plots were established immediately after burning with three different levels of charcoal input (C0, removal of all visible charcoal; C1, charcoal retained in-situ; C2, charcoal removed from C0 added to C2) and an unburnt control (UB). Thirty-two soil indicators representing soil physical, chemical, and biological properties were determined. The results showed that 11 indicators exhibited significant differences among the treatments, with significantly lower SOM, microbial biomass carbon (MBC), peroxidase (POD) and leucine aminopeptidase (LAP) activities for the C0 and C1 plots than the UB plots (P < 0.05), while no significant difference was observed between the UB and C2 plot (P > 0.05). The soil available N, P and exchangeable nutrient contents were not significantly different among the treatments (P > 0.05). Our results indicate that SOM and microbial attributes did not recover five years after the disturbance event and that charcoal appeared to play a positive role in the post-fire soil restoration. Whether the accelerated recovery of soil restoration induced by charcoal might contribute to higher forest productivity needs to be testified in combination with plant growth and performance analysis in the future.