Increased mean annual temperatures coupled with management strategies of US national forests have produced conditions conducive to widespread bark beetle induced forest mortality. This study focused specifically on the spruce beetle (Dendroctonus rufipennis) and its host, Engelmann spruce (Picea engelmanii). Upon tree death, the soil environment undergoes changes with respect to soil water and nutrient availability. The large one-time input of nitrogen (N)-rich needles has been shown to effect nutrient cycling by microbes. However, information regarding the effects of beetle kill on belowground microbial communities is limited. The objective of this study was to investigate dynamics of microbial community structure and function as well as changes to the soil environment following beetle kill using a chronosequence approach, in Southeastern Wyoming. In order to address these objectives, high throughput Illumina sequencing of the soil fungal and bacterial communities coupled with analysis of extracellular enzyme activity were utilized to describe belowground microbial dynamics following spruce beetle infestation.
Results/Conclusions
Our study demonstrated increased gravimetric water content as well as higher pH in dead stands as compared to healthy and infested stands. In addition to the changes in edaphic parameters, we observed increased extracellular enzymatic activity and turnover of the fungal community in dead compared with live stands, demonstrated by lower proportional abundances of ectomycorrhizal fungi (ECM) as well as a relative increase in saprotrophic taxa. The bacterial community also changed over time as infestation progressed, with higher levels of pathogenic taxa present in dead stands. Our findings show the soil environment to be dramatically affected by bark beetle infestation; as demonstrated by increased microbial activity and community turnover, both of which potentially affect forest stand regeneration as well as carbon and nutrient cycling following disturbance.