Abstract. Substantial input of exogenous organic matter (EOM) may be required to offset the projected decline in soil organic carbon (SOC) stocks in croplands caused by global warming. However, information on the effectivity of EOM application dose in preserving SOC stocks is surprisingly limited. Therefore, we set up a 90-day incubation experiment with large soil volumes (sandy loam and silt loam) to compare the mineralization of EOM (¹³C-labelled ryegrass) and SOC as a function of three EOM application doses (0.5, 1.5, and 5 g dry matter kg^-1 soil). In the sandy loam soil, the percentage of mineralized EOM was not affected by EOM dose, while SOC mineralization increased proportionally with increasing EOM dose (+49.6 mg C per g EOM). In the silt loam soil, the percentage of mineralized EOM decreased somewhat with increasing dose, while SOC mineralization increased at a higher rate than in the sandy loam soil (+117.2 mg C per g EOM). In both textured soils, increasing EOM dose possibly supplied energy for microbial growth and enzyme production, which in turn stimulated mineralization of native SOC (i.e. co-metabolism). Higher soil macroporosity at higher EOM doses in the silt loam soil could have contributed to sustaining aerobic conditions (indicated by soil Eh) and promoting SOC priming as shown by positive relationships between pore neck size classes 43–60, 60–100 and >300 μm and SOC priming, suggesting a new mechanism for understanding SOC priming. In sum, this experiment and our previous research suggest that EOM mineralization is mostly independent of EOM dose, but EOM dose modulates mineralization of native SOC. These findings tentatively indicate that using larger EOM doses could help preserve more of added EOM-C in silt loam soils, but longer-term confirmation in the field will firstly be required before we could draw any conclusion for soil C management.

中文翻译：

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土壤有机碳矿化受外源有机质施用剂量控制

摘要。可能需要大量外源有机物（EOM）输入来抵消全球变暖造成的农田土壤有机碳（SOC）储量预计下降。然而，有关 EOM 应用剂量在保存 SOC 库存方面的有效性的信息却非常有限。^{因此，我们在大土壤体积（沙壤土和淤泥壤土）中进行了为期 90 天的培养实验，以比较 EOM（ 13} C 标记的黑麦草）和 SOC的矿化与三种 EOM 施用剂量（0.5、1.5、和 5 g 干物质 kg ^-1土壤）。在沙壤土中，矿化 EOM 的百分比不受 EOM 剂量的影响，而 SOC 矿化随着 EOM 剂量的增加而成比例增加（+49.6 mg C/g EOM）。在粉砂壤土中，矿化 EOM 的百分比随着剂量的增加而有所下降，而 SOC 矿化的增加速度高于砂壤土（+117.2 mg C/g EOM）。在两种纹理土壤中，增加 EOM 剂量可能为微生物生长和酶产生提供能量，从而刺激天然 SOC 的矿化（即共代谢）。粉质壤土中较高 EOM 剂量下较高的土壤大孔隙率可能有助于维持有氧条件（由土壤 Eh 表示）并促进 SOC 启动，如孔颈尺寸等级 43-60、60-100 和 >300 μm 之间的正相关关系所示和 SOC 启动，提出了一种理解 SOC 启动的新机制。总之，本实验和我们之前的研究表明，EOM 矿化基本上与 EOM 剂量无关，但 EOM 剂量调节天然 SOC 的矿化。这些发现初步表明，使用较大的 EOM 剂量有助于在淤泥壤土中保留更多添加的 EOM-C，但在我们对土壤 C 管理得出任何结论之前，首先需要在现场进行长期确认。