Understanding soil organic matter (SOM) stability and carbon storage under long-term intensive land management systems is vital for estimating the C sequestration potentials of agricultural lands. Available methods currently used for measuring the stability of SOM, such as radiocarbon dating, are expensive. However, a cost-effective and reliable stable isotope-based model was developed for grasslands which utilizes the C/N ratio and δN of soils to determine the stability of SOM. We applied this model to test for the first time its usefulness for evaluating SOM stability in the top and subsoils of a subtropical paddy field cultivated for 37 years. We also compared paddy soil's SOM stability and carbon storage under different fertilizer treatments. Treatments evaluated were a control (CK), inorganic fertilizer (NPK), NPK+cattle manure (NPKM), and NPK+rice straw (NPKS). Results showed that the C/N ratios and δN signatures of POM and mOM proved effective in predicting SOM stability as predicted by the model. SOM stability increased with depth across the treatments, especially in NPKM and NPKS in the deeper soil layer compared to CK and NPK. Introducing δ13 C as an indicator further strengthened the model, revealing higher δ13 C accumulation in the subsoils, indicating higher C sequestration. Further insights showed that unlike in the CK treatment, the use of NPKM and NPKS significantly increased SOC accumulation by increasing the proportion of mineral-protected organic matter (mOM) compared to the microbial-accessible particulate organic matter (POM). The abundance of mOM associated with a lower rate of decomposition in the paddy fields and the incorporation of higher 13 C in the subsoils under NPKM and NPKS were key factors that enhanced the long-term increase in organic C and SOM stability. Thus, the stable isotope-based model proved a reliable proxy for estimating SOM stability in paddy fields.

中文翻译：

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使用基于碳和氮稳定同位素的模型评估耕作稻田土壤中的长期有机碳动态和有机质稳定性

了解长期集约化土地管理系统下土壤有机质（SOM）的稳定性和碳储存对于估算农田的碳固存潜力至关重要。目前用于测量 SOM 稳定性的可用方法（例如放射性碳测年）价格昂贵。然而，针对草原开发了一种经济有效且可靠的基于稳定同位素的模型，该模型利用土壤的 C/N 比和 δN 来确定 SOM 的稳定性。我们首次应用该模型来测试其在评估耕种了 37 年的亚热带稻田表层和底土中 SOM 稳定性的有效性。我们还比较了不同施肥处理下水稻土的有机质稳定性和碳储量。评估的处理包括对照（CK）、无机肥（NPK）、NPK+牛粪（NPKM）和NPK+稻草（NPKS）。结果表明，POM 和 mOM 的 C/N 比和 δN 特征证明可以有效预测模型预测的 SOM 稳定性。与 CK 和 NPK 相比，SOM 稳定性随着处理深度的增加而增加，尤其是在更深土层的 NPKM 和 NPKS 中。引入 δ13 C 作为指标进一步强化了模型，揭示了地下土中更高的 δ13 C 积累，表明更高的碳封存。进一步的研究表明，与 CK 处理不同，NPKM 和 NPKS 的使用通过增加矿物质保护的有机物 (mOM) 与微生物可接触的颗粒有机物 (POM) 的比例，显着增加了 SOC 积累。稻田中 mOM 的丰度与较低的分解速率相关，以及 NPKM 和 NPKS 下底土中较高 13 C 的结合是增强有机 C 和 SOM 稳定性长期增加的关键因素。因此，基于稳定同位素的模型被证明是估算稻田 SOM 稳定性的可靠代理。