Soil nutrient availability and stoichiometry shape microbial community composition 2 years after wildfire

Introduction The response of soil microbial communities to fire-induced changes in nutrients is a key determinant of post-fire ecosystem dynamics. In Pinus sylvestris forests, we investigated how bacterial and fungal communities are shaped by nutrient availability and soil stoichiometric relationships 2 years after wildfire across a gradient of fire severity. Methods We analyzed soils from unburned, low-severity, and high-severity fire conditions. Soil carbon fractions, including total, organic, inorganic, and pyrogenic carbon, nitrogen, available phosphorus, and stoichiometric ratios (C:N, C:P, and N:P) were quantified. Bacterial and fungal communities were characterized using 16S rRNA gene and ITS amplicon sequencing, respectively. Results Available phosphorus and nutrient stoichiometric ratios were key drivers of microbial community composition 2 years after fire. Fungal taxa associated with nutrient concentrations or ratios showed balanced responses, with similar proportions of fungal communities being positively and negatively affected. In contrast, several prokaryotic taxa showed positive associations with post-fire nutrient conditions and appeared to benefit from them, including Microbacteriaceae, Geodermatophilaceae, and Sphingomonadaceae. Discussion The identification of specific microbial families linked to nutrient availability highlights their potential as indicators of soil recovery. These findings demonstrate the importance of soil stoichiometric relationships in shaping microbial communities in post-fire ecosystems and contribute to a better understanding of soil recovery processes by linking nutrient dynamics with microbial changes after fire.