Pyrogenic carbon contribution to tropical savanna soil carbon storage

Savannas are fire-prone ecosystems that contribute substantially to global burned area and fire emissions, but these emissions may be offset by the deposition of fire-derived, recalcitrant pyrogenic carbon (PyC) in soils. However, the magnitude of the PyC contribution to soil organic carbon (SOC) storage in savannas and factors driving its accumulation in soils remain unknown due to a lack of measurements with consistent methods in the literature. To address this knowledge gap, we sampled 253 sites at a regional scale across tropical savannas in Kruger National Park, South Africa, covering broad gradients in fire regimes, grass biomass, rainfall, and soil texture. We demonstrate that across these savannas, pyrogenic carbon contributes, on average, 14.08% (se = 0.36%, n = 253) of total SOC storage in surface soils but can reach as high as 40%. While fire frequency and grass biomass affect soil PyC stock, savannas with higher soil clay content and lower rainfall-conditions that favor PyC preservation-tend to accumulate more PyC in the soil. These results underscore the significant contribution of PyC to SOC and support the idea that fire produced PyC is a key pathway for carbon sequestration in tropical savannas.