Building and protecting soil organic carbon (SOC) are critical to agricultural productivity, soil health, and climate change mitigation. We aim to understand how mechanisms at the organo-mineral interfaces influence SOC persistence in three contrasting soils (Luvisol, Vertisol, and Calcisol) under long-term free air CO₂ enrichment conditions. A continuous wheat-field pea-canola rotation was maintained. For the first time, we provided evidence to a novel notion that persistent SOC is molecularly simple even under elevated CO₂ conditions. We found that the elevated CO₂ condition did not change the total SOC content or C forms compared with the soils under ambient CO₂ as identified by synchrotron-based soft X-ray analyses. Furthermore, synchrotron-based infrared microspectroscopy confirmed a two-dimensional microscale distribution of similar and less diverse C forms in intact microaggregates under long-term elevated CO₂ conditions. Strong correlations between the distribution of C forms and O–H groups of clays can explain the steady state of the total SOC content. However, the correlations between C forms and clay minerals were weakened in the coarse-textured Calcisol under long-term elevated CO₂. Our findings suggested that we should emphasize identifying management practices that increase the physical protection of SOC instead of increasing complexity of C. Such information is valuable in developing more accurate C prediction models under elevated CO₂ conditions and shift our thinking in developing management practices for maintaining and building SOC for better soil fertility and future environmental sustainability.

中文翻译：

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揭示长期二氧化碳浓度升高下土壤有机碳如何在精细尺度上表现：一项为期 8 年的自由空气二氧化碳富集研究


建立和保护土壤有机碳 (SOC) 对于农业生产力、土壤健康和减缓气候变化至关重要。我们的目的是了解在长期自由空气 CO ₂ 富集条件下，有机矿物界面的机制如何影响三种对比土壤（Luvisol、Vertisol 和 Calcisol）中 SOC 的持久性。麦田豌豆-油菜籽的连续轮作得以维持。我们第一次为一个新概念提供了证据，即即使在 CO ₂ 升高的条件下，持久 SOC 在分子上也是简单的。我们发现，与基于同步加速器的软 X 射线分析确定的环境 CO ₂ 下的土壤相比，升高的 CO ₂ 条件并没有改变总 SOC 含量或 C 形态。此外，基于同步加速器的红外显微光谱证实了在长期升高的 CO ₂ 条件下完整微聚集体中相似且多样性较低的 C 形式的二维微尺度分布。粘土的 C 形式和 O-H 基团分布之间的强相关性可以解释总 SOC 含量的稳态。然而，在长期升高的CO ₂ 下，粗质地钙溶胶中C 形态与粘土矿物之间的相关性减弱。我们的研究结果表明，我们应该强调确定增加 SOC 物理保护的管理实践，而不是增加 C 的复杂性。这些信息对于在 CO ₂ 升高的条件下开发更准确的 C 预测模型并转变我们的思维非常有价值开发维护和建设 SOC 的管理实践，以提高土壤肥力和未来环境的可持续性。