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, persistent pyrogenic carbon (PyC) in soils. While some estimates of PyC contributions to soil organic carbon (SOC) storage in savanna exist, factors driving its accumulation in soils remain largely 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 storage in tropical savannas and highlight the environmental factors associated with its accumulation across regional scales, providing an empirical basis for understanding fire’s role in the tropical savanna carbon cycle.热带稀树草原是一类易受火灾干扰的生态系统，其对全球火烧面积与火灾排放的贡献显著，但此类火灾排放可被火成因持久性热解碳（pyrogenic carbon, PyC）在土壤中的沉积所抵消。尽管已有部分研究估算了热带稀树草原中热解碳对土壤有机碳（soil organic carbon, SOC）储量的贡献，但由于现有文献中缺乏采用统一方法开展的测量工作，驱动热解碳在土壤中累积的相关因素仍在很大程度上尚不明确。为填补这一认知空白，我们在南非克鲁格国家公园的热带稀树草原区域范围内布设了253个采样点，采样覆盖了火灾制度、草本生物量、降雨量以及土壤质地的广泛梯度。本研究表明，在该区域的热带稀树草原中，热解碳平均占表层土壤总有机碳储量的14.08%（标准误=0.36%，样本量n=253），最高可达40%。尽管火灾频率与草本生物量会对土壤热解碳储量产生影响，但土壤黏粒含量更高、降雨量更低的稀树草原——这类环境更利于热解碳的保存——往往会在土壤中累积更多的热解碳。本研究结果证实了热解碳对热带稀树草原土壤有机碳储量的重要贡献，同时明确了区域尺度上与其累积相关的环境因素，为理解火灾在热带稀树草原碳循环中的作用提供了实证依据。