Medium-term response of soil bacterial communities to two post-fire management strategies after a large wildfire

Post-fire management strategies, such as straw mulching (SM) and cutting plus lopping (CpL), are applied to reduce erosion and promote ecosystem recovery. However, their medium-term effects on soil bacterial communities remain poorly understood. This study addresses this gap by analysing bacterial community responses 3-4 years after fire under SM and CpL treatments. We hypothesized that (i) post-fire management affects bacterial communities, with effects declining over time, and (ii) the magnitude and direction of these effects depend on the type of post-fire treatment. Soil samples were collected from treated, untreated burned, and unburned plots. Bacterial diversity and composition were characterised using 16S rRNA gene sequencing. Alpha diversity metrics (rarefied richness, Shannon's diversity, Simpson's dominance) showed no significant differences, although dominance was significantly higher in CpL plots in the third year (p = 0.046). Beta diversity, assessed by PCA, revealed significant changes in the fourth year between SM and untreated burned plots (p = 0.012), whereas CpL plots were significantly different in both years (p = 0.011 and p = 0.014). In both treatments, functional trends indicated that anaerobic decomposers increased during the third post-treatment year, while nitrifying and nitrogen-fixing bacteria increased during the fourth year. These results demonstrate that post-fire treatments shape the composition and functional trajectories of soil bacterial communities. Cutting plus lopping has a stronger influence on bacterial community composition than straw mulching over medium-term timescales. In general, the microbial responses should be considered when planning post-fire ground cover treatments to support soil restoration and reduce erosion.