Short term effects of fire on assembly rules and β-diversity of soil bacteria in Mediterranean soils

Fires are common in Mediterranean soils and constitute an important driver of their evolution; however, their effects on the assembly rules of soil bacteria received limited attention. We reanalyzed the data from Aponte et al. (2022), retrieved from the NCBI database, to investigate fire-induced short term effects on R-diversity, abundance ranking, and the co-occurrence patterns among bacterial OTUs under the pyrodiversity-biodiversity hypothesis. Higher richness and abundance of bacterial OTUs were recorded in the burnt compared to the unburnt areas. Although a-diversity was unaffected, beta-diversity based on Bray Curtis similarity index decreased by fire. The beta-ratio analyzing the two components of beta-diversity (nestedness and turnover) was >0.5 in unburnt and <0.5 in burnt area, denoting the predominance of stochastic and deterministic regulation, respectively. The Zero- Sum Model showed the best fit to the abundance data of the local communities followed by the deterministic Zipf-Mandelbrot model. Fire increased the dispersion between the local communities, while taxa niche diversification was less strict compared to the unburnt soils. Fire disconnected the co-occurrence bacterial network, but networks in both burnt and unburnt areas exhibited modular architecture with Small-World properties and increased robustness to broadly distributed disturbances. However, fire increased the vulnerability of bacterial network to targeted disturbances. The robustness to widespread disturbances such as fire was likely related to the long evolutionary history of organisms inhabiting the Mediterranean soils.