Biological nitrogen fixation dynamics during ecosystem recovery in longleaf pine savannas
Tierney, Julie Anne
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Biological nitrogen fixation (BNF) can alleviate nitrogen (N) deficiencies that inhibit ecosystem recovery, yet how BNF achieves this under frequent fire disturbance is unclear. We investigated BNF’s capacity to provide N to restored longleaf pine savannas, how it is organized and regulated over time, and how it responds to fire. We conducted this study in 54 1-ha plots of longleaf pine across gradients of stand age and fire frequency at two sites in the southeastern US. We determined BNF by three functional groups of N-fixers (legumes, soil crusts, and asymbiotic bacteria), and quantified components of the N cycle. We found that BNF was maintained over time, and fire enhanced BNF from legumes. Despite this, BNF was insufficient to balance N losses from fire. Unexpectedly, differences between the two sites described the most variation in BNF, highlighting that landscape-level drivers can have dramatic influences on BNF.