Post-fire restoration strategies shape long-term soil biogeochemical recovery and microbial communities in boreal permafrost ecosystems

Abstract

Climate-driven wildfires are intensifying threats to boreal permafrost soils risking their ecological integrity and long-term carbon storage. Restoring post-fire microbial resilience and biogeochemical restoration is therefore critical for global conservation and climate mitigation. We evaluate the long-term effects of contrasting restoration pathways on soil physicochemical properties, enzyme activities, and microbial community composition 37 years after a wildfire in boreal forests of northeast China. Using a randomized complete block design, we compared three active restoration strategies: secondary successional forest (SSF), plantation forest (PF), and agroforestry (AF), against an unburned natural forest (UNF) reference benchmark. Analyses of 72 soil samples included key nutrients, enzyme activities, and metagenomic sequencing. Results showed that AF and SSF maintained soil organic carbon (SOC; 33.3 ± 4.53 and 29.02 ± 4.86 g kg⁻¹, respectively), while PF exhibited substantially lower values (SOC: 18.8 ± 1.26 g kg⁻¹), representing reductions of 43.5% in SOC relative to AF. Acid phosphatase activity, a key indicator of phosphorus cycling, was significantly higher in AF and SSF than in PF. Agroforestry supported the highest bacterial Shannon diversity, while the unburned natural forest (UNF) maintained the highest fungal diversity. Microbial community composition shifted markedly: PF was dominated by Proteobacteria, with Acidobacteria depleted, whereas AF was dominated by Actinobacteriota. We conclude that by enhancing organic matter inputs, microbial diversity, and enzyme-mediated nutrient cycling, AF and SSF outperform PF in restoring soil ecological processes, thereby accelerating long-term ecosystem restoration in permafrost regions.