Abstract The increase of carbon (C) in the pedoderm (0–50 mm soil layer) improves ecosystem functioning and stability. This study evaluated quantitative and qualitative C responses to grazing intensity in the pedoderm of grassland and savanna ecosystems. These ecosystems differ in terms of soil properties, climate, vegetation quality and livestock density. Three commercial farms were chosen from each ecosystem. Each farm exhibited two grazing intensities (heavy and light grazing) by livestock which induced poor and good forage quality, respectively. Vegetation quality changes were observed along a gradient of grazing pressure, with respect to the distance from the water point. Soil samples of the pedoderm were taken in each of the two zones to analyse the effects of grazing on soil quality parameters. Soil samples were analyzed for soil organic carbon (SOC), soil inorganic carbon (SIC), labile and humic C fractions. The SOC structure was determined with 13C NMR spectroscopy. Indices of the extent of SOC decomposition were calculated. Grazing pressure per se did not influence soil C fractions. However, clayey grassland soils in the cool-moist climate exhibited more resilience to C losses than sandy savanna soils under hot-dry climatic conditions. Thus, comparisons between the two ecosystems showed that on average, all C fractions were 35–97% higher in the clayey moist-cool grassland ecosystem compared to the sandy dry-hot savanna ecosystem, regardless of the grazing pressure. A decline in O-alkyl C (7%) with concomitant increase in recalcitrant alkyl C (6%) in the grassland ecosystem, indicated that constant animal trampling induced SOC decomposition, and loss of labile C fractions in the heavily grazed zones. Molecular composition of SOC in the savanna ecosystem was more influenced by plant functional types, thus C allocation patterns, than decomposition.

中文翻译：

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南非半干旱和干旱商业农场土壤碳动态的跨牧场比较

摘要 土壤表层（0-50 毫米土壤层）中碳 (C) 的增加改善了生态系统的功能和稳定性。本研究评估了草地和稀树草原生态系统的土壤中对放牧强度的定量和定性碳响应。这些生态系统在土壤特性、气候、植被质量和牲畜密度方面各不相同。从每个生态系统中选择了三个商业农场。每个农场的牲畜表现出两种放牧强度（重放牧和轻放牧），分别导致草料质量差和好。沿放牧压力梯度观察到植被质量的变化，与水点的距离有关。在两个区域中的每一个区域都采集了足皮的土壤样本，以分析放牧对土壤质量参数的影响。分析土壤样品的土壤有机碳 (SOC)、土壤无机碳 (SIC)、不稳定和腐殖质 C 部分。SOC 结构由 13C NMR 光谱确定。计算了 SOC 分解程度的指标。放牧压力本身不影响土壤碳含量。然而，在干热气候条件下，凉爽潮湿气候下的粘土质草地土壤比沙质稀树草原土壤表现出更大的碳损失恢复能力。因此，两个生态系统之间的比较表明，与沙质干热热带稀树草原生态系统相比，无论放牧压力如何，粘土湿凉草原生态系统中的所有 C 分数平均高 35-97%。O-烷基 C (7%) 下降，同时草原生态系统中顽固的烷基 C (6%) 增加，表明持续的动物践踏会导致 SOC 分解，以及重度放牧区不稳定 C 部分的损失。热带稀树草原生态系统中 SOC 的分子组成受植物功能类型的影响更大，因此 C 分配模式，而不是分解。