Fire has been an integral evolutionary force shaping and maintaining grassy biomes, such as the Afromontane grasslands of South Africa. Afromontane grasslands represent a large carbon reservoir, but it is uncertain how fire affects their long-term C storage. We investigated the effect of fire regime on soil organic C and N (SOC; SON) in a long-term (39-year) burning experiment in the Maloti-Drakensberg Park, South Africa. We compared SOC and SON sampled in 2004 and 2019 from six treatments differing in fire frequency (annual, biennial, five-year, infrequent) and season (spring, autumn). Average SOC increased significantly between 2004 and 2019. Average SON increased slightly, resulting in a significant increase in C:N ratio, indicating that soil organic matter is becoming less N-eutrophic. Importantly, burning annually in spring increased SOC and SON. This unexpected response is attributed to the aluandic (acidic, high organic matter) properties of Drakensberg soils. Burning in autumn did not increase SOC and SON. The lowest C stocks were observed in infrequently burnt plots. Average C sequestration across all fire treatments was 0.30 Mg ha⁻¹ y⁻¹. The observed increase in SOC under frequent fires is contrary to many findings from other studies in grassy ecosystems and notably driven by fire season.

火一直是塑造和维持草地生物群落的不可或缺的进化力量，例如南非的非洲山地草原。非洲山地草原代表了一个巨大的碳储库，但尚不确定火灾如何影响它们的长期碳储存。我们在南非马洛蒂-德拉肯斯堡公园的一项长期（39 年）燃烧实验中调查了火势对土壤有机碳和氮（SOC；SON）的影响。我们比较了 2004 年和 2019 年从火灾频率（一年一次、两年一次、五年一次、不频繁）和季节（春季、秋季）不同的六种处理中采样的 SOC 和 SON。2004 年至 2019 年平均 SOC 显着增加。平均 SON 略有增加，导致 C:N 比显着增加，表明土壤有机质正变得不那么富营养化。重要的，每年春季燃烧会增加 SOC 和 SON。这种意想不到的反应归因于德拉肯斯堡土壤的 aluandic（酸性、高有机质）特性。秋季燃烧并没有增加 SOC 和 SON。在不经常烧毁的地块中观察到最低的 C 库存。所有火灾处理的平均碳封存量为 0.30 Mg ha^-1是^-1。在频繁火灾下观察到的 SOC 增加与其他草地生态系统研究的许多发现相反，尤其是受火灾季节的驱动。