Abstract:

Soil iron reduction under anaerobic conditions is closely related to carbon cycle, however, the relationship between dissimilar iron reduction and carbon mineralization in paddy soil is still insufficiently understood. In this experiment, the paddy soil in Mengjin, Henan Province in the middle and lower reaches of the Yellow River was selected as the study object, and the soil was divided into 50.0, 100, 200, and 400 mg, respectively. Magnetite (Fe₃O₄) powder was added to 3.00 g paddy soil, and constant temperature anaerobic mud culture experiment was set up. During the culture experiment, the changes of CO₂ and CH₄ emissions in the extractable Fe(Ⅱ), water-soluble organic carbon (WSOC), water-soluble inorganic carbon (WSIC), and the form of iron oxide in the soil were dynamically monitored. The results showed that exogenous addition of Fe₃O₄ could significantly increase the soil iron reduction potential by 0.88-4.53 mg•kg⁻¹, but had no significant effect on the maximum iron reduction rate and iron reduction rate constant. The addition of Fe₃O₄ significantly increased the content of WSIC (88.4 mg•kg⁻¹), decreased the content of WSOC (62.7 mg•kg⁻¹), and weakened the decomposition of soil organic carbon by microorganisms and the risk of CO₂ expulsion. Increasing Fe₃O₄ supplemental level had no significant effect on the cumulative CO₂ emissions, but significantly inhibited the cumulative soil CH₄ emissions, with a decreasing value between 11.1-76.3 mg•kg⁻¹ and a maximum decrease of 56.3%, indicating that exogenous Fe₃O₄ supplementation reduced the risk of soil carbon mineralization. After the end of the culture, the cumulative emissions of CO₂ and CH₄ of the mineralized products showed a significant increasing trend, and the highest value reached 174%, indicating that CH₄ emission was significantly inhibited with the increase of exogenous Fe₃O₄ addition during the culture cycle, while the distribution of liquid phase mineralized products was significantly increased with the increase of exogenous Fe₃O₄ addition, with the maximum increase of 15%, indicating that the anaerobic culture was foreign. The correlation analysis showed that the free iron oxide (Fe_d) of soil Fe reduction potential was significantly and negatively correlated with the cumulative emission of CH₄ and the emission rate of CH₄, indicating that the alienated iron reduction enhanced by exogenous Fe₃O₄ supplementation significantly inhibited the mineralization of soil organic carbon. The results are of great significance for further understanding the mechanism of dissimilated iron reduction and its coupled carbon conversion in rice soil.

Key words: paddy soil, dissimilatory iron reduction, Fe₃O₄, carbon mineralization

摘要：

厌氧条件下土壤铁还原与碳循环紧密相关，然而针对稻田土壤中异化铁还原与碳矿化关系的认识尚有不足。采用黄河中下游地区河南孟津稻田土壤为研究对象，分别将50.0、100、200、400 mg磁铁矿（Fe₃O₄）粉末添加至3.00 g稻田土壤，设置恒温厌氧泥浆培养实验，期间动态监测土壤0.5 mol•L⁻¹ HCl可提取态Fe(Ⅱ)、水溶性有机碳（WSOC）、水溶性无机碳（WSIC）、铁氧化物形态、CO₂和CH₄排放的变化。结果表明，外源添加Fe₃O₄可显著提高土壤铁还原潜势，增幅为0.883－4.53 mg•kg⁻¹，但对最大铁还原速率和铁还原速率常数无显著影响；添加Fe₃O₄显著提高了WSIC含量，增加值达88.4 mg•kg⁻¹，降低了WSOC含量，降低值为62.7 mg•kg⁻¹，减弱微生物对土壤有机碳分解作用及CO₂的外排风险；提高Fe₃O₄添加量对CO₂累积排放量无显著影响，但显著抑制了土壤CH₄的累积排放量，降低值介于11.1－76.3 mg•kg⁻¹，降幅最高达56.3%，表明外源添加Fe₃O₄降低了土壤碳矿化风险；培养结束后矿化产物CO₂与CH₄累积排放量占比呈现显著增长趋势，最高值可达174%，表明培养周期内CH₄排放随外源Fe₃O₄添加量增加而被显著抑制，液相矿化产物分配占比则随外源Fe₃O₄添加量增加显著增加，增幅最大达15%，表明厌氧培养中外源Fe₃O₄添加可显著抑制温室气体排放。相关分析显示，土壤Fe还原潜势、游离态铁氧化物（Fe_d）与CH₄累积排放量和CH₄排放速率均呈现出极显著负相关关系，表明外源添加Fe₃O₄增强的异化铁还原显著抑制了土壤有机碳的矿化。研究结果对进一步理解水稻土壤异化铁还原及其耦合的碳转化机理具有重要意义。

关键词: 稻田土壤, 异化铁还原, Fe₃O₄, 土壤碳矿化, 温室气体, 土壤有机碳