Soil organic carbon and black carbon storage and dynamics under different fire regimes in temperate mixed-grass savanna

[1] We quantified the effects of repeated, seasonal fires on soil organic carbon (SOC), black carbon (BC), and total N in controls and four fire treatments differing in frequency and season of occurrence in a temperate savanna. The SOC at 0–20 cm depth increased from 2044 g C m⁻² in controls to 2393–2534 g C m⁻² in the three treatments that included summer fire. Similarly, soil total N (0–20 cm) increased from 224 g N m⁻² in the control to 251–255 g N m⁻² in the treatments that included summer fire. However, winter fires had no effect on SOC or total N. Plant species composition coupled with lower δ¹³C of SOC suggested that increased soil C in summer fire treatments was related to shifts in community composition toward greater relative productivity by C₃ species. Lower δ¹⁵N of soil total N in summer fire treatments was consistent with a scenario in which N inputs > N losses. The BC storage was not altered by fire, and comprised 13–17% of SOC in all treatments. Results indicated that fire and its season of occurrence can significantly alter ecosystem processes and the storage of C and N in savanna ecosystems.