Straw return as a common and effective management can improve soil carbon (C) sequestration and structure by forming aggregates and aggregate associated C. Quantifying soil aggregation and aggregate associated C is key to predicting soil organic C dynamics using testable models. The relative quantity of C stabilized in soil aggregate is an indicator that can reveal the conversion efficiency of added straw to organic C in aggregate. Straw size is known to alter litter decomposition, but how straw size impacts the dynamics of soil aggregate formation and the relative quantity of C stabilized in soil aggregate after litter addition is not well understood. We conducted an 80-day laboratory incubation with wheat straw addition of two different sizes (1–2 mm and <0.25 mm) to artificial soils of two textures (3 % clay and 7 % clay). The objectives were to examine 1) whether straw size significantly modified litter decomposition and the relative quantity of C stabilized in soil aggregates over time, and 2) what soil physical and biochemical factors determined soil aggregation and the formation of aggregate-associated C over time, such as straw size, soil texture, or enzyme activity. We found that both litter decomposition and the relative quantity of C stabilized in soil aggregates were higher in the treatment with small straw addition than those with large straw addition, but they were not significantly different between two soils with 3 % vs. 7 % clay content. This was due to increased enzyme activities caused by small straw addition, which could enhance dissolved organic C generation and stimulate microbial decomposition. Additionally, the mass proportion of macroaggregate (>2 mm) increased with time while the mass proportion of microaggregate (0.25–2 mm) decreased, suggesting that microaggregate combined to form macroaggregate (>2 mm) in the late stage of incubation (after day 17). Moreover, the relative quantity of C stabilized in microaggregate (<0.053 mm) increased linearly with dissolved organic C, whereas the relative quantity of C stabilized in macroaggregate (>2 mm) increased with the aromaticity of dissolved organic matter as measured by specific ultraviolet absorbance at 254 nm. Together, our findings suggest that straw size remarkably modifies litter decomposition and the relative quantity of C stabilized in soil aggregates by changing the quantity and quality of dissolved organic C at different decomposition stages, whereas small difference in soil clay content has no effects.

中文翻译：

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随着时间的推移，少量秸秆的添加可增强秸秆分解并稳定土壤团聚体中的碳

秸秆还田作为一种常见且有效的管理方法，可以通过形成团聚体和团聚体相关碳来改善土壤碳 (C) 固存和结构。量化土壤团聚体和团聚体相关碳是使用可测试模型预测土壤有机碳动态的关键。土壤团聚体中稳定碳的相对量是反映添加秸秆向团聚体中有机碳转化效率的指标。众所周知，秸秆大小会改变凋落物分解，但秸秆大小如何影响土壤团聚体形成的动态以及添加凋落物后土壤团聚体中稳定的碳的相对数量尚不清楚。我们进行了 80 天的实验室孵化，将两种不同尺寸（1-2 毫米和 <0.25 毫米）的麦秆添加到两种质地（3% 粘土和 7% 粘土）的人造土壤中。目的是检查 1) 秸秆大小是否显着改变凋落物分解以及土壤团聚体中碳的相对数量随着时间的推移而稳定，以及 2) 哪些土壤物理和生化因素决定了土壤团聚以及随着时间的推移团聚体相关碳的形成，例如秸秆大小、土壤质地或酶活性。我们发现，少量秸秆添加处理的凋落物分解和土壤团聚体中稳定的碳相对量均高于大量秸秆添加处理，但在粘土含量为 3% 和 7% 的两种土壤之间没有显着差异。 。这是由于少量秸秆添加导致酶活性增加，可以增强溶解性有机碳的生成并刺激微生物分解。此外，随着时间的推移，大团聚体（>2 mm）的质量比例增加，而微团聚体（0.25-2 mm）的质量比例下降，这表明微团聚体在孵化后期（一天后）结合形成大团聚体（>2 mm）。 17）。此外，微团聚体（<0.053 mm）中稳定的 C 相对量随溶解有机 C 线性增加，而大团聚体（> 2 mm）中稳定的 C 相对量随溶解有机物的芳香度（通过比紫外吸光度测量）增加而增加。 254 nm。总之，我们的研究结果表明，秸秆大小通过改变不同分解阶段溶解有机碳的数量和质量，显着改变凋落物分解和土壤团聚体中稳定的碳的相对数量，而土壤粘土含量的微小差异则没有影响。