[Effect of Fire-deposited Charcoal on Soil Organic Carbon Pools and Associated Enzyme Activities in a Recently Harvested Pinus massoniana Plantation Subjected to Broadcast Burning]

Charcoal is a carbonaceous particulate matter with a highly aromatic structure produced by incomplete combustion, and it can cause persistent long-term effects on soil ecological functions. In this study, we determined soil organic carbon pools and associated enzyme activities following five years of different charcoal treatments[charcoal removal (B₀), charcoal retained in situ (B₁), and the addition of charcoal removed from B₀(B₂)] and the unburnt control (UB) in a recently harvested Pinus massoniana plantation subjected to broadcast burning. The results showed that dissolved organic carbon (DOC), microbial biomass carbon (MBC), coarse and fine particulate organic carbon (CPOC and FPOC), and recalcitrant carbon (RC) contents were significantly lower in B₁ than those in UB soil (P<0.05). The MBC and FPOC contents of B₂ soil were comparable to those of UB soil, which were significantly higher than those of B₀ soil (P<0.001). There was no difference in MBC/TC between the B₂ and UB soils, whereas MBC/TC was significantly lower in B₀ than in UB soil (P<0.05). β-glucosidase and peroxidase activities of B₀, B₁, and B₂ soils were significantly lower than that of UB soil (P<0.01), and polyphenol oxidase activity was significantly lower in B₀ and B₂ soils than in UB soil (P<0.01). No significant difference in soil TC, DOC, readily oxidized carbon (ROC), CPOC, and RC content as well as associated enzyme activities was observed among the charcoal treatments (P>0.05). Redundancy analysis showed that sucrose and polyphenol oxidase were the key drivers influencing soil organic carbon fractions, accounting for 16.3% and 12.7% of the total variance, respectively. Overall, our findings indicated that fire-deposited charcoal played a positive role in enhancing soil microbial biomass carbon recovery, soil organic carbon accumulation, and stability, highlighting the importance of charcoal in the management of subtropical plantations in the future.