Purpose

Applying carbon-rich materials, such as those resulting from pyrolysis (biochar) or composting (compost), to the agro-ecosystems has been proven to improve soil organic carbon (SOC) storage and reduce CO₂ emissions. However, it is not clear how earthworms drive changes in soil C sequestration and mineralization under biochar/compost incorporation.

Materials and methods

A 288-day microcosm experiment was conducted to investigate the effects of earthworms on the concentrations of SOC and its fractions, the structural characteristics of SOC and CO₂ emissions following three straw incorporation treatments (maize straw, maize straw compost, and maize straw biochar), and no straw addition was used as the control. Each treatment had two variants: one with earthworms (Eisenia nordenskioldi) and one without earthworms. The elemental analysis, ¹³C NMR spectroscopy, and three-dimensional fluorescence technologies were used to characterize the features of SOC.

Results and discussion

Results indicated that the incorporation of straw, compost, and biochar significantly improved the SOC contents compared with the control. Earthworms did not affect the SOC fractions in the control soil but led to the increase in SOC and humic acid (HA) under compost incorporation. The molecular structures of HA showed features pointing to high degrees of humification and aromaticity, as presented by elemental composition, fluorescence intensities, and ¹³C NMR. The increase of SOC and a slight reduction of CO₂ emission in compost-amended soil could be attributed to the accumulation of more stable HA caused by earthworms. In contrast, earthworm presence decreased the aromaticity of HA in biochar-amended soil, and made its structure more hydrophilic, which was not conducive to C sequestration. In addition, the mineralization of microbial C by earthworms also led to an increased CO₂ emission from biochar-amended soil.

Conclusions

Earthworms weaken the ability of biochar to reduce soil CO₂ emissions but improve the C sequestration capacity of compost-amended soil. This study improves our understanding of the contributions of soil macrofauna on the SOM formation and stabilization after incorporation of different maize straw-derived materials.

中文翻译：

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在掺入不同的玉米秸秆衍生材料后，蚯蚓如何影响土壤有机碳含量和 CO2 排放

目的

将富含碳的材料，例如热解（生物炭）或堆肥（堆肥）产生的材料应用于农业生态系统，已被证明可以改善土壤有机碳 (SOC) 储存并减少 CO ₂排放。然而，在生物炭/堆肥掺入下，蚯蚓如何驱动土壤固碳和矿化的变化尚不清楚。

材料和方法

进行了为期 288 天的微观实验，研究了蚯蚓对3 种秸秆掺入处理（玉米秸秆、玉米秸秆堆肥和玉米秸秆生物炭）后 SOC 及其组分浓度、SOC 和 CO ₂排放的结构特征的影响，并且没有添加秸秆作为对照。每种处理都有两种变体：一种含有蚯蚓（Eisenia nordenskioldi），另一种不含蚯蚓。采用元素分析、¹³ C NMR光谱和三维荧光技术表征SOC的特征。

结果和讨论

结果表明，与对照相比，秸秆、堆肥和生物炭的掺入显着提高了 SOC 含量。蚯蚓不影响对照土壤中的 SOC 分数，但导致堆肥掺入下 SOC 和腐殖酸 (HA) 的增加。HA 的分子结构显示出指向高度腐殖化和芳香性的特征，如元素组成、荧光强度和¹³ C NMR 所示。SOC增加，CO ₂略有减少堆肥改良土壤中的排放可归因于蚯蚓引起的更稳定的 HA 的积累。相比之下，蚯蚓的存在降低了生物炭改良土壤中 HA 的芳香性，使其结构更加亲水，不利于 C 封存。此外，蚯蚓对微生物C的矿化也导致生物炭改良土壤中CO ₂排放量增加。

结论

蚯蚓削弱了生物炭减少土壤CO ₂排放的能力，但提高了堆肥改良土壤的固碳能力。这项研究提高了我们对掺入不同玉米秸秆衍生材料后土壤大型动物对 SOM 形成和稳定的贡献的理解。