FPC Updates

Understanding soil microbial responses to wildfires is critical for climate adaptation and ecosystem recovery. This study spans the Chilean Coastal Cordillera, from the Atacama Desert (arid) to a temperate forest, a fire-prone climatic gradient. We hypothesized that soil texture and porosity determine the resilience of microbial reac­ tivation and enzyme activity following a wildfire. This study examined the impact of short-term (20 min) heating at 300, 600, or 900 ◦C on enzyme activity (β-glucosidase, urease, peroxidase, and phosphatases), microbial biomass, and reactive oxygen species in four Chilean soils: arid, semi-arid, Mediterranean, and temperate. Furnace heating simulated near-surface wildfire exposure and was contextualized with a 1-D conduction model that yielded temperature–time profiles and cumulative thermal load (degree-hours). Responses scaled with thermal load, with higher exposure increasing soil organic matter (SOM) loss, reducing Vmax and biomass, and raising H2O2. After heating, the soils were cooled and incubated for 48 h under sterile conditions to isolate residual activity and early reactivation. At 900 ◦C, SOM retention was higher in temperate clay-rich soils (0.68%) than in arid sandy soils (0.02%). Within 48 h of heating at 300–600 ◦C, microbial biomass recovered to ~70% in temperate soils but remained <10% in arid soils. At 900 ◦C, the thermal load ranged from ~336 to ~1368 kJ across soils. Hydrogen peroxide concentration peaked at 3.5 μmol g- 1 in semi-arid soils, indicating elevated oxidative stress. Peroxidase retained ~90% of its catalytic efficiency at 300 ◦C in temperate soils, whereas β-glucosidase activity in arid soil dropped below 10% after heating at 900 ◦C. These findings confirm that higher porosity and SOM buffer the impact of heat, accelerate microbial reactivation, and mitigate oxidative stress. After accounting for initial soil C, N, and pH, texture effects persisted, reinforcing the need for targeted interventions in coarse-textured low-OM soils.

Carolina Merino:

carolina.merino@ufrontera.cl

Merino C, Jofré I, Stock S, Nájera F, Matus F, Kuzyakov Y, Aburto F, Dörner J, Rubilar R, Dippol MA. 2026. Return of soil function: texture and thermal load drive post-fire microbial reactivation. Applied Soil Ecology. 219: 106819. DOI: https://doi.org/10.1016/j.apsoil.2026.106819

• Simulated heating

• Soil enzyme activity

• Soil texture

• Microbial biomass

• Reactive oxygen species (ROS

• Post-fire recovery depends on heat dose and thermal load predicts SOM loss.

• In 48 h, clay-rich temperate soils regain ∼70% biomass; arid sands <10%.

• Porosity protects and clays buffer heat, keep enzymes active, speed reactivation.

• In arid sands oxidants surge and functions crash; at 900 °C signals are residual.