Effects of Fire Intensity on Soil Microbial Ecology in a Grassland Ecosystem

In temperate grasslands, periodic or seasonal burning is considered critical for maintaining plant diversity and ecosystems. Under global change scenarios such as warmer and wetter climates and increasing alien invasions, fire is predicted to increase in intensity in many ecosystems. While the effects of fire on many terrestrial habitats (e.g., grassland, forest) have been extensively studied, less attention has been paid to the effects of fire intensity on the underlying soil microbiome. In this study, we used metagenomics, via 16S rRNA amplicon sequencing, coupled with functional assays and thermal profiling, to investigate the effects of increased fire intensity on the short- and medium-term composition and functionality of grassland soil microbiomes. The results indicated that an increase in fire calorific output had a short-term negative effect on soil microbial activity in grassland plots supplemented with plant biomass to simulate increases in fire intensity. In turn, the taxonomic profiling of soil microbial communities revealed that these plots were enriched in fast-growing bacterial taxa 4 weeks after the fire event when compared to plots without biomass supplementation. This suggests that increased fire intensity exerts a medium-term effect on the recovery of grassland soil microbiomes.