PS 12-106 - Low-intensity fire alters litter and soil bacterial communities in a fire-managed pine savanna ecosystem

Background/Question/Methods

In fire-affected ecosystems, bacterial communities fulfill important functions related to fuel decomposition and nutrient cycling that should affect future fire regimes and ecosystem management. Yet, these bacterial communities are studied almost exclusively in ecosystems affected by high intensity wildfires. Lower fire intensities and more frequent fires should have nuanced effects on bacterial communities and their ecosystem functions.

We used 16S rDNA sequencing to study the compositional responses of the litter and soil bacterial communities in burnt and unburnt patches that were near and away from dominant longleaf pine trees, following a recent low intensity prescribed fire in an old-growth pine savanna system with a long history of patchy, recurrent, low intensity fire.

Results/Conclusions

We found that bacterial communities clearly separated by different substrate and fire treatment combinations. These community shifts were driven primarily by changes in the relative abundances of a subset of more rare, less abundant influential bacterial families. Both substrate and fire effects were significant toward affecting bacterial family abundances both individually and in tandem, with substrate explaining more variation than fire effects.

Plant communities and soil variables did not strongly affect bacterial communities. Rather, the ecosystem’s fire history and its diverse substrate heterogeneity, altered further by recurrent, low intensity fires, likely enabled proliferation or hindrance of influential families to drive larger bacterial community variation.

This work identifies strong associations of influential families with specific substrate*fire treatments, and emphasizes the importance of continuing fire management that generates the substrate heterogeneity to which influential families respond. Changes in bacterial communities and influential families may have important effects on ecosystem functions that affect future fire regimes and ecosystem management.