Abstract Afforestation contributes to soil organic carbon (SOC) sequestration and the restoration of degraded soil. However, the changes in SOC stock following afforestation on sloping land are poorly understood. Here we conduct a quantitative review that synthesizes 239 observations from 31 studies to evaluate the effects of slope gradients on the changes in SOC stock in three soil layers (0–20 cm, 20–40 cm and 40–60 cm) following afforestation, considering previous land cover (cropland and grassland) and tree type (broadleaf and conifer). In the topsoil layer, slope gradient has a significant effect on the changes in SOC stock: slope gradient positively relates to SOC stock change and significantly predicts the SOC stock change after controlling for temperature, precipitation, stand age, and initial SOC stock. Soil gradient explains 12.5% of the variance. We find a significant decrease in SOC stock after the afforestation of gentle slopes with a gradient lower than 10% but a significant increase in SOC stock on slopes with a gradient higher than 30%. Afforestation on sloping cropland results in an increase in SOC stock, especially in the upper soil, while afforestation on grassland results in an increase in SOC stocks only on very steep slopes (gradient >60%). Tree type has a limited effect on changes in SOC after afforestation on sloping land. However, conifers show a greater SOC sequestration potential in deeper soils and on steep slopes with a gradient higher than 60%, while broadleaf trees sequester more SOC in topsoil and on slopes with a gradient of 30–60%. The present study suggests that to increase SOC sequestration, priority should be given to afforestation with conifers on steep cropland.

中文翻译：

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造林改变坡地土壤有机碳储量：先前土地覆盖和树木类型的作用

摘要 植树造林有助于土壤有机碳（SOC）固存和退化土壤的恢复。然而，人们对坡地植树造林后 SOC 储量的变化知之甚少。在这里，我们进行了一项定量审查，综合了 31 项研究的 239 项观察结果，以评估坡度梯度对造林后三个土壤层（0-20 厘米、20-40 厘米和 40-60 厘米）SOC 储量变化的影响，考虑到以前的土地覆盖（农田和草地）和树木类型（阔叶树和针叶树）。在表土层，坡度梯度对 SOC 储量的变化有显着影响：坡度梯度与 SOC 储量变化呈正相关，在控制温度、降水、林龄和初始 SOC 储量后显着预测 SOC 储量变化。土壤梯度解释 12。5% 的方差。我们发现坡度低于 10% 的缓坡植树造林后 SOC 储量显着减少，但坡度高于 30% 的坡度上的 SOC 储量显着增加。在倾斜农田上植树造林导致 SOC 储量增加，特别是在上层土壤中，而草地植树造林仅在非常陡峭的斜坡（梯度 >60%）上导致 SOC 储量增加。树种对坡地植树造林后SOC变化的影响有限。然而，针叶树在较深的土壤和坡度高于 60% 的陡坡上表现出更大的 SOC 封存潜力，而阔叶树在表土和坡度为 30-60% 的坡度上封存更多的 SOC。本研究表明，为了增加 SOC 封存，