Despite the importance of South Africa's Afromontane grasslands for ecosystem services (water supply and biodiversity), soil organic carbon (SOC) research remains limited. These grasslands evolved with fire, and fire exclusion leads to native plant afforestation. This study investigated SOC fractions and origin to understand the impact of fire‐exclusion‐driven afforestation and aspect on SOC storage in Afromontane grasslands. This study in Cathedral Peak Research Catchments, initiated in the 1940s, compared an afforested fire‐excluded site (AF) to a periodically burnt (accidental fires, 2–5 years interval) grassland (PB) within the same catchment (Catchment‐IX). Additionally, it compared a south‐facing periodically burnt grassland (Catchment‐IX) to a north‐facing biennially burnt grassland (Catchment‐VI). Soil samples collected at soil‐depth increments (0–5, 5–10, 10–15, 15–20, 20–30, 30–60 and 60–100 cm) revealed that, within Catchment IX, PB had more topsoil SOC stocks and microbial activity than AF but similar active carbon (C) concentrations. As expected, δ13C values revealed that SOC in PB originates from C4 grasses, whilst it mostly originates from C3 plants in AF. The south‐facing slope (Catchment‐IX) had more SOC stocks, microbial activity and active C compared to the north‐facing slope (Catchment‐VI). Fire‐exclusion‐driven afforestation changed SOC input from roots to litter, thus reducing SOC storage. Cooler south‐facing slopes are better C reservoirs. Afromontane grasslands show greater potential for C sequestration than afforested systems.

中文翻译：

---

南非大教堂峰 Afromontane 草原防火和坡向对土壤碳组分的影响


尽管南非的非洲山地草原对于生态系统服务（供水和生物多样性）非常重要，但土壤有机碳（SOC）研究仍然有限。这些草原是随着火而进化的，排除火会导致本土植物造林。本研究调查了 SOC 分数和来源，以了解防火驱动的造林和方面对 Afromontane 草原 SOC 存储的影响。这项在大教堂峰研究集水区开展的研究于 20 世纪 40 年代启动，将同一集水区 (集水区-IX) 内的绿化防火场地 (AF) 与定期燃烧（意外火灾，间隔 2-5 年）的草地 (PB) 进行了比较。此外，还将朝南的周期性燃烧草地（集水区-IX）与朝北的两年一次燃烧的草地（集水区-VI）进行了比较。以土壤深度增量（0-5、5-10、10-15、15-20、20-30、30-60 和 60-100 厘米）收集的土壤样本显示，在流域 IX 内，PB 具有更多的表土 SOC种群和微生物活性高于 AF，但活性炭 (C) 浓度相似。正如预期的那样，δ13C 值显示 PB 中的 SOC 来源于 C4 禾本科植物，而 AF 中的 SOC 主要来源于 C3 植物。与朝北的斜坡（集水区-VI）相比，朝南的斜坡（集水区-IX）具有更多的有机碳储量、微生物活性和活性碳。防火驱动的造林改变了 SOC 从根部到凋落物的输入，从而减少了 SOC 存储。凉爽的朝南斜坡是更好的碳库。非洲山地草原比植被系统显示出更大的固碳潜力。