Prescribed Burns Drive Lasting Changes in Soil Nitrogen Cycling and Microbial Function

Abstract

Fire can be a major pulse disturbance to soil microbial communities. Yet regular burning is a natural and essential process that maintains biodiversity and the unique attributes of rare and imperiled fire-dependent ecosystems. Most studies of fire effects on soil microbial communities typically focus on short-term (<1 year) responses following a single fire event. Here we examined the longer-term effects of repeated prescribed fire at the Albany Pine Bush--a fire-dependent, inland pitch pine (Pinus rigida) barren ecosystem of the northeastern US. We observed that this long-term fire management (i.e., a fire interval of approximately every 5 to 13 years over the past 30 years) has led to substantial depletion of soil nitrogen, specifically nitrate. However, we found no lasting shifts in the higher-level taxonomic composition of soil prokaryotic communities. Instead, metagenomic analysis revealed significant changes in the nitrogen-cycling functional potential, specifically, decreased dissimilatory nitrate reduction and denitrification potential in repeatedly burned soils. Collectively, these data suggest fire-induced geochemical changes persist under repeated burning, potentially driving substantial shifts in soil microbial functional diversity. Our study reveals strain-level changes that would be missed when examining only higher-level taxonomic patterns. Where fire is repeatedly applied, fire-induced shifts in soil microbial communities can persist well beyond a few weeks after burning--challenging prevailing views of short-lived belowground effects of prescribed burns.