Abstract

Wildfires reshape soil microbial functions that sustain nutrient cycling and carbon storage in managed forest landscapes. Recovery was slower in plantation soils with low pH and high exchangeable Al content. The central hypothesis predicted a longer persistence of post-fire acidity and exchangeable Al in burned Pinus radiata plantations than in burned Nothofagus stands. A 0, 4, 6, 12, and 22 yr fire chronosequence tested this prediction in volcanic Andisols. Acidity was measured as water pH, and Al availability was measured as KCl-exchangeable Al. Along the pH-Al gradient, Shannon diversity, hydrolytic enzyme activity, and MicroRespTM substrate-use breadth were predicted to be lower where pH remained low and exchangeable Al remained high. Bray-Curtis distance from paired unburned controls was predicted to be larger under the same chemical conditions. Soil chemistry, extracellular enzymes, full-length 16S rRNA profiles, and MicroRespTM assays were used to quantify taxonomic and functional recovery. The burned pine soils ranged from pH 4.6 at 0 yr to pH 6.1 at 6 yr. Olsen P in native unburned soils increased from 4.0 to 13.7 mg kg-1 during the first 6 yr. Native soils reached higher beta-glucosidase and acid phosphatase activity during the first decade. Pine soils reached early polyphenol oxidase and peroxidase peaks and delayed aminopeptidase and cellulolytic activities. The MicroRespTM profiles matched the enzyme portfolios. Native soils respired more carbohydrates and organic acids, whereas pine soils respired more amino acids. The functional separation between burned and unburned plots narrowed by 22 yr, whereas native soils retained a broader substrate breadth. Models associated native activity with pH and exchangeable Al and associated plantation activity with total C and Olsen P. These results define stand-specific recovery pathways and identify pH and exchangeable Al as candidate management targets for post-fire recovery in plantations on volcanic Andisols.