This study investigated the change in soil organic carbon (SOC), soil labile carbon (C), soil total nitrogen (N), particulate organic carbon (POC), mineralizable soil C (Min-C) in soil aggregate fractions, and soil particles size at 0–30 cm soil depth of the semi-steppe rangelands in Central Iran (Sheida and Khargosh regions). The study used a fully randomized design with four land uses in the rangelands including covered with rainfed wheat (CR0), abandoned rangelands (ARs) for 5–15 years (AR15), abandoned rangeland for 16–40 years (AR40), and permanently uncultivated rangelands (UR) as the reference sites that were replicated three times (n = 3) with at most 2 km distance from each other in an area of 25 ha. For each treatment, the soil samples were randomly obtained at 0–30 cm soil depth in three replicated plots of 2 × 2 m using a core size of 7 cm in diameter. The samples were mixed to take a composite soil sample (12 soil samples in each region) in June 2018. The results indicated that soil POC is the most sensitive fraction for the identification of shifts in the total SOC after the cultivation cessation because by increasing the abandoned land and the cessation of cropland activities, the POC has also increased. In conclusion, after the cessation of rainfed cropping and the recovery of natural vegetation, the increases in soil microorganism activity can result in a higher nutrient cycling in the degraded rangeland ecosystems.

中文翻译：

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农业废弃对土壤有机碳的影响：以伊朗中部半草原牧场为例

本研究调查了土壤团聚体组分中土壤有机碳 (SOC)、土壤不稳定碳 (C)、土壤总氮 (N)、颗粒有机碳 (POC)、可矿化土壤碳 (Min-C) 和土壤颗粒中的变化伊朗中部（Sheida 和 Khargosh 地区）半草原牧场 0-30 cm 土壤深度的大小。该研究采用完全随机设计，牧场有四种土地用途，包括覆盖雨育小麦 (CR0)、废弃牧场 (ARs) 5-15 年 (AR15)、废弃牧场 16-40 年 (AR40) 和永久未开垦的牧场（UR）作为参考站点，重复了 3 次（n = 3) 在 25 公顷的区域内，彼此之间的距离最多为 2 公里。对于每种处理，使用直径为 7 cm 的核心尺寸在三个 2 × 2 m 的重复地块中随机获取 0-30 cm 土壤深度的土壤样品。于 2018 年 6 月将样品混合制成复合土壤样品（每个区域 12 个土壤样品）。结果表明，土壤 POC 是识别停耕后总 SOC 变化最敏感的部分，因为通过增加废弃土地和停止耕地活动，POC 也有所增加。总之，在雨养作物停止和自然植被恢复后，土壤微生物活性的增加可导致退化牧场生态系统中更高的养分循环。