Agricultural practices that promote the formation of soil organic matter (SOM) are considered important climate change mitigation strategies by increasing resilience to climate shocks and promoting soil carbon sequestration. Efforts to increase root production and depth distribution through planting deep rooted crops and selective crop breeding have been identified as a promising strategy to achieve these goals. However, we lack a complete understanding of how the decomposition of roots in the deep soil (e.g., below 30 cm), contributes to SOM formation and stabilization. Here using unique soil-biomass microcosms in the field to trace 13C enriched root litter to a depth of 90 cm, we show that as decomposition dynamics change with depth, so do the SOM formation pathways. At our study site, root residues decomposed faster in the top 0–30 cm, achieving 97 % mass loss by 13 months of incubation compared to 77 % and 81 % in the 30–60 and 60–90 cm depths, respectively. Litter derived carbon (LDC) was preferentially recovered as stable mineral associated organic matter (MAOM), primarily within aggregates, with 67 % more in the 0–30 cm than in the 60–90 cm depth. At depth, root residues decomposed slower and accumulated as the less stable particulate organic matter (POM) within macroaggregates with 145 % more LDC recovered in light POM in the 60–90 cm depth than the 0–30 cm depth. We found that bulk SOM measurements were too coarse to elucidate the likely fate of newly incorporated litter in the soil, but our detailed fractionation demonstrated the relative contribution of new root inputs to functionally different SOM pools, MAOM and POM, and allowed us to interpret the role of microaggregates in these dynamics in new detail, particularly microaggregates within macroaggregates (i.e., occluded microaggregates). Our results highlight the importance of balancing the trade-off between MAOM and POM formation when considering strategies to enhance both carbon sequestration and soil health in agroecosystems. If POM is critical for aggregate formation and microaggregates play an important role in MAOM formation, efforts to increase soil carbon sequestration need to focus on both fractions and on supporting overall soil structure.

中文翻译：

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深度对土壤中根系碳稳定机制的介导影响：MAOM 和 POM 途径之间的权衡


促进土壤有机质 （SOM） 形成的农业实践被认为是重要的气候变化缓解策略，可以提高对气候冲击的抵御能力并促进土壤碳封存。通过种植深根作物和选择性作物育种来增加根系产量和深度分布的努力已被确定为实现这些目标的有前途的策略。然而，我们对深层土壤（例如，30 厘米以下）中根系的分解如何促进 SOM 的形成和稳定缺乏完整的了解。在这里，使用田间独特的土壤生物量微观世界将富含 13C 的根凋落物追踪到 90 厘米的深度，我们表明，随着分解动力学随深度的变化，SOM 的形成途径也会发生变化。在我们的研究地点，根残基在顶部 0-30 厘米处分解得更快，在孵育 13 个月时质量损失了 97%，而在 30-60 厘米和 60-90 厘米深度中，质量损失分别为 77% 和 81%。凋落物衍生碳 （LDC） 优先作为稳定矿物伴生有机物 （MAOM） 回收，主要在聚集体中，0-30 cm 深度比 60-90 cm 深度多 67%。在深处，根残基分解较慢，并在大团聚体中积累为不稳定的颗粒有机物 （POM），在 60-90 cm 深度的轻型 POM 中回收的 LDC 比 0-30 cm 深度高 145%。 我们发现，大量 SOM 测量太粗糙，无法阐明土壤中新掺入的凋落物的可能命运，但我们的详细分馏证明了新根输入对功能不同的 SOM 池 MAOM 和 POM 的相对贡献，并使我们能够以新的细节解释微团聚体在这些动态中的作用。 特别是大聚集体中的微聚集体（即封闭的微聚集体）。我们的结果强调了在考虑加强农业生态系统碳封存和土壤健康的策略时，平衡 MAOM 和 POM 形成之间权衡的重要性。如果 POM 对团聚体的形成至关重要，并且微团聚体在 MAOM 的形成中起着重要作用，那么增加土壤碳封存的努力需要集中在组分和支持整体土壤结构上。