土壤有机质 (SOM) 通常被分成可操作的物理部分，例如颗粒有机物 (POM) 和矿物相关有机物 (MAOM)，以提高我们对 SOM 持久性的理解。虽然通常假设 POM 和 MAOM 具有不同的生物地球化学特征，但 POM 和 MAOM 的组成以及与异质土壤中总 SOM 分解的关系在何处以及为何存在差异仍未得到解决。我们分析了 156 个土壤样品中 POM 和 MAOM 的元素、同位素和化学成分，包括漫反射红外傅里叶变换 (DRIFT) 光谱，这些土壤样品来自 20 个国家生态观测站网络 (NEON) 站点，这些站点跨越北部不同的生态系统（苔原到热带）美国。我们对 POM (53–2000 μm) 和 MAOM (< 53 μm) 化学分散后。C/N 值，δ13 C 和 C-H（脂肪族）/CO 的 DRIFT 光谱在不同土壤中的 POM 和 MAOM 组分中是相关的，并且通常相似；C C（芳香族）/C的漂移光谱O 在分数之间通常相似但不相关。一个普遍的假设认为 MAOM 以微生物来源的 OM 为主，但我们的研究结果表明，植物来源的 OM 也可以对 MAOM 做出重大贡献，特别是在年降水量 > 1200 mm 的湿森林中（MAOM C/N > 15）。多项统计分析表明，MAOM 的 C 数量和化学成分可以像 POM 的测量一样有效地预测 18 个月孵化期间土壤 C 的分解。因此，POM 和 MAOM 都可能在几个月的时间尺度上对分解做出重大贡献，这可能是因为 POM 和 MAOM 的特征通常是相关的和/或 MAOM 的大池大小可以弥补其相对于 POM 的较低分解率。此外，我们发现土壤地球化学成分（如淤泥和粘土、钙、草酸盐可提取的铁和铝）以及气候和生态系统类型，可以部分预测 POM 和 MAOM 之间的数量和组成差异。总体而言，土壤中 POM 和 MAOM 之间的相对耦合与去耦是基于地球化学可预测的，这些相似/差异提供了对不同生态系统中植物源性 MAOM 来源变化的洞察。MAOM 对短期土壤碳分解的重要性可能被低估了。这些相似性/差异提供了深入了解不同生态系统中植物源性 MAOM 来源的变化。MAOM 对短期土壤碳分解的重要性可能被低估了。这些相似性/差异提供了深入了解不同生态系统中植物源性 MAOM 来源的变化。MAOM 对短期土壤碳分解的重要性可能被低估了。

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Soil organic matter (SOM) has often been separated into operational physical fractions, such as particulate organic matter (POM) and mineral-associated organic matter (MAOM), to improve our understanding of SOM persistence. While it is generally assumed that POM and MAOM have distinct biogeochemical characteristics, it remains unresolved where and why POM and MAOM differ in their composition and relationships to total SOM decomposition among heterogenous soils. We analyzed elemental, isotopic, and chemical composition, including diffuse reflectance infrared Fourier transform (DRIFT) spectra, of POM and MAOM in 156 soil samples collected from 20 National Ecological Observatory Network (NEON) sites spanning diverse ecosystems (tundra to tropics) across North America. We used a classic size separation method for POM (53–2000 μm) and MAOM (1200 mm annual precipitation (with MAOM C/N > 15). Multiple statistical analyses showed that C quantity and chemical composition of MAOM could as effectively predict soil C decomposition during an 18-month incubation as measures of POM. Thus, POM and MAOM both likely contributed significantly to decomposition over timescales of months, possibly because characteristics of POM and MAOM were often related and/or a large pool size of MAOM could compensate for its lower decomposition rate relative to POM. Further, we found that soil geochemical composition (such as silt and clay, calcium, oxalate-extractable iron and aluminum), along with climate and ecosystem type, could partly predict differences in quantity and composition between POM and MAOM. Overall, relative coupling vs. decoupling between POM and MAOM among soils was predictable based on geochemistry, and these similarities/differences provide insight into variation in the plant-derived sources of MAOM across diverse ecosystems. The importance of MAOM to short-term soil C decomposition has probably been underappreciated.