LongTerm Prescribed Fire Soil Bacteria

Prescribed fires are common in forest management, yet we lack a clear picture of how prescribed fire intervals impact the soil systems. Here, we present evidence of microbial community and soil chemistry shifts following sixty years of continuous prescribed fire interval manipulation in the Olustee Experimental Forest in Northeastern Florida. We investigated three fire interval treatments (1year, 2 years, and 4 years) in addition to a comparable control treatment without fire in over sixty years. Excluding the O horizon that was absent in the most frequent fire treatments, we sampled three mineral soil horizons (A, E, and B) to elucidate prescribed fire impacts across the soil profile. Our results indicate that only the topmost A horizon was affected by the fire interval manipulations, whereas the deeper E and B horizons were minimally impacted. Richness of both bacterial and fungal communities in recurring fire treatments was higher than and their community composition different from those in the fire exclusion control in the A horizon. Similar to the biotic soil attributes, fire interval treatments altered soil chemistry only in the A horizon: the frequent prescribed burns (one-, two-, four-year fire intervals) had higher total nitrogen, total carbon, phosphorus, and NH4+ than the fire exclusion treatment; the soil chemistry of the deeper E and B horizons did not differ among the treatments. The soil chemistry correlated with the microbial community composition, especially when comparing the more frequent burns to the fire exclusion treatment. Indicator taxon analyses identified fire-responsive bacteria and fungi, such as Ktedonobacteria sp. and an unclassified ascomycete that were abundant in the fire exclusion treatment and the ectomycorrhizal Russula spp. that were most abundant in the annual burn treatment. The different fire intervals also impacted fungal guilds suggesting shifts in community function. The fire exclusion treatment was enriched with ectomycorrhizal, lichenized, and wood saprotrophic fungi, whereas the annual burn treatment was enriched with arbuscular mycorrhizal fungi compared to the other treatments. Given the many roles of microbial communities in soil systems, our results suggest that recurring prescribed fires change the soil microbial communities and their function as well as soil chemistry, although mainly only in the uppermost soil horizon.