Impact of Forest Fires on Soil Microbial Substrate Utilization and Dehydrogenase Activity in Different Rock Types and Soil Layers

ABSTRACT This study explored the effects of forest fires on soil microbial activity in forest soils classified by rock origin (igneous, metamorphic, and sedimentary) and stratified by subsoil depth (topsoil, subsoil). Microbial activity, indicated by average well color development (AWCD) and Shannon diversity indices, was higher in undamaged topsoils compared to fire‐damaged ones. In contrast, fire‐damaged subsoils, particularly in metamorphic and sedimentary soils, exhibited increased microbial activity over time due to organic matter decomposition. A significant increase in substrate utilization was observed in undamaged soils across all rock types (* p < 0.05, ** p < 0.01) in topsoil, with sedimentary rock exhibiting the highest microbial diversity based on Shannon indices. The dehydrogenase activity followed a similar pattern, with reduced activity in fire‐damaged topsoil but higher activity in damaged metamorphic and sedimentary subsoils. Principal component analysis (PCA) linked microbial indicators (AWCD, Shannon index) to mineral compositions like orthoclase and hornblende, highlighting the role of soil chemistry in shaping microbial responses to fire. These insights advance the understanding of fire‐induced changes in soil microbial functions across diverse geological contexts.