Nutrient availability and microbial traits constrained by soil texture modulate the impact of forest fire on gross nitrogen mineralization

Wildfire is a primary disturbance of forests and has been expected to influence soil nitrogen (N) transformation. However, the effect of fire on soil gross N mineralization is still under debate. This study used the 15N dilution and Miseq sequencing techniques to examine the impact of fire history on soil nutrient availability, microbial traits, and gross N mineralization rates at five forest sites. Results showed that fire had both positive and negative effects on soil gross N mineralization, depending on sampling sites. Fire promoted gross N mineralization rates by 41–49% in fine-textured soils by increasing dissolved organic C and N concentrations, microbial abundances, and microbial interactions (connectance of microbial co-occurrence networks) in soil. In contrast, fire decreased the rates by 24–44% in coarse-textured soils by reducing the above measurements. The results suggest that the effect of fire on soil gross N mineralization is regulated by soil texture. This study provides insights into the complex mechanisms of how fire affects soil gross N mineralization in forest ecosystems.