Wildfire Impacts on Soil Microbiomes: Potential for Disruptions to Nitrogen-Cycling Bacteria

Abstract

Wildfires have become increasingly common across the United States in recent decades, with significant implications for ecosystem health and sustainability. The viability and metabolic activity of soil bacteria are key for maintaining global nitrogen-cycling processes and are likely to be impacted as burn severity continues to increase. To this end, wildfire-affected soils were studied to examine the impact on nitrogen-cycling bacteria in soils affected by low, moderate, and high wildfire severities. This objective was achieved by characterizing soil bacterial communities in control (i.e., unburned) and burned soils collected one year following the Woolsey wildfire (Los Angeles and Ventura Counties, CA, USA) using Illumina MiSeq 16S sequencing and profiling nitrogen-cycling gene expression using quantitative reverse transcription polymerase chain reaction (qRT-PCR). Six families and 17 genera were significantly (Spearman r_s > |0.4|; p < 0.05) negatively associated with wildfire severity, and three families and six genera were significantly positively associated with wildfire severity. Many of these taxa contain species that are known to be critical contributors to maintaining global nitrogen cycles. NosZ and NirS nitrifying genes had significantly lower transcription rates in high-severity samples compared with control and low/moderate-severity samples. Collectively, these results suggest that high-severity wildfires significantly negatively alter the community structures and functions of nitrogen-cycling bacteria, which may have significant ramifications for ecosystem recovery in postwildfire landscapes.