Scotland is continuing to afforest land in order to combat climate change, but the long-term capacity for carbon sequestration in forest soils is still uncertain. Here we present measurements that provide comparative estimates of soil organic carbon in grassland and forestry sites at steady state. We develop a new approach to interpret these values based on simulation of organic carbon turnover in soils that are accumulating carbon and use this to determine losses due to management operations associated with afforestation of grassland and deforestation/reforestation of forest stands. Soil organic carbon stock changes were studied in a >120 year-old Scots pine chronosequence and adjacent grassland sites on podzolic soils. Significant carbon accumulation was measured in the top organic soil horizons with forest age, while no changes were noted in the deeper mineral soil horizons. The simulations with the RothC-26.3 model revealed that pine forests on sandy soils could lose a significant amount of soil organic carbon through management operations. The lowest modeled stocks of soil organic carbon were not in the young sites (0–25 years old), but at 43 years since reforestation. Using measured data from our study site, the simulations of grassland afforestation suggested that accumulation of organic carbon under forest occurs mainly in the organic horizons, while the deeper sandy mineral soil horizons are likely to become depleted in organic carbon compared to grasslands. Our simulations suggest that afforestation of grasslands would increase overall soil carbon stocks but may deplete the more stable carbon pools in the deeper mineral horizons of the podzols.

中文翻译：

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使用建模解释森林土壤有机碳测量变化的新方法；苏格兰灰化土壤上 200 年松树年代序列的案例

苏格兰正在继续造林土地以应对气候变化，但森林土壤长期固碳能力仍不确定。在这里，我们提出了一些测量值，这些测量值提供了草原和林业场地在稳定状态下土壤有机碳的比较估计。我们开发了一种新方法来解释这些值，基于模拟积累碳的土壤中的有机碳周转率，并使用它来确定由于与草地造林和森林砍伐/重新造林相关的管理操作造成的损失。在 120 年历史的苏格兰松树年序和邻近的灰化土壤上的草地地点研究了土壤有机碳库的变化。随着森林年龄的增长，在顶层有机土壤层中测量到显着的碳积累，而在更深的矿质土壤层中没有发现任何变化。RothC-26.3 模型的模拟表明，沙质土壤上的松林可能会通过管理操作损失大量的土壤有机碳。土壤有机碳的最低模拟储量不在年轻的地点（0-25 岁），而是在重新造林后 43 年。使用来自我们研究地点的测量数据，草地造林模拟表明，森林下有机碳的积累主要发生在有机层，而与草原相比，更深的沙质矿质土壤层可能会耗尽有机碳。我们的模拟表明，草地植树造林会增加土壤总碳储量，但可能会耗尽灰化土更深矿物层中更稳定的碳库。