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

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 δ 13 C of SOC suggested that increased soil C in summer fire treatments was related to shifts in community composition toward greater relative productivity by C 3 species. Lower δ 15 N 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.