Abstract:

Rare earth tailings soil is barren and deficient in carbon and nitrogen, severely restricting ecological restoration. This study explored the effects of adding active and inactivated microalgae on soil carbon and nitrogen sequestration and aggregate structures. Chlorella pyrenoidosa and nitrogen-fixing Anabaena azotica were selected, and three groups of experiments (active, inactivated, and control) were set up. A total of 20 mL of the algal solution was added weekly for 105 days. The chlorophyll content on the soil surface was measured on days 15, 45, and 105, and the soil carbon, nitrogen, and aggregate indicators were determined on day 105. The results showed that: 1) Active microalgae increased the soil organic carbon (SOC) and total nitrogen (TN) contents by 151% and 512% compared with the control, respectively, while the inactivated treatment increased them by 171% and 385%, respectively. The TN content in the active group was significantly 26.2% higher than that in the inactivated group, whereas the SOC content in the inactivated group was 7.80% higher than that in the active group. 2) The net increases of SOC and TN in the active treatment reached 1.476 g·kg⁻¹ and 0.564 g·kg⁻¹, accounting for 32.4% and 79.0% of the total amounts, respectively; those in the inactivated treatment were 1.832 g·kg⁻¹ and 0.415 g·kg⁻¹, accounting for 37.3% and 73.5%, respectively. 3) The inactivated treatment increased coarse particulate organic carbon (CPOC) by 111% compared with the control, whereas the active treatment significantly increased fine particulate organic carbon (FPOC) and mineral-associated organic carbon (MAOC) by 124% and 153%, respectively. Both treatments increased the total particulate nitrogen by 533% and 396% compared with in that the control. 4) On day 105, the surface soil chlorophyll contents in the active and inactivated treatments increased by 142% and 106% compared to the initial levels, respectively. 5) The addition of microalgae significantly reduced the proportion of silt and clay particles. The active and inactivated treatments increased the mean weight diameter (MWD) of aggregates by 10.3% and 18.3%, respectively, and the geometric mean diameter (GMD) in the active group increased by 10.8%. This study indicates that active and inactivated microalgae synergistically improve carbon and nitrogen sequestration efficiency through photosynthetic carbon fixation and biological nitrogen fixation, promote the formation of aggregates, and provide a new approach for the ecological restoration of tailings. This study clarifies the impact of microalgae restoration on carbon and nitrogen transformation, providing a theoretical foundation for optimizing soil improvement technologies.

Key words: microalgae, rare earth tailings, carbon and nitrogen sequestration, aggregates, ecological restoration

摘要： 稀土尾矿砂土壤贫瘠、碳氮匮乏，严重制约生态修复。通过添加活性、灭活微藻探究其对土壤碳氮固持及团聚体结构的改良效应。选用小球藻（Chlorella pyrenoidosa）、固氮鱼腥藻（Anabaena azotica），设置活性、灭活及对照3组试验，每周添加20 mL藻液，共持续105 d，分别于第15、45、105天测定土表叶绿素含量，于第105天测定土壤碳氮、团聚体指标。结果表明，1）与对照相比，活性微藻使总有机碳（SOC）和总氮（TN）含量分别提高151%和512%，灭活处理组分别提升171%和385%，活性组TN显著高于灭活组26.2%，灭活组SOC较活性组高7.80%。2）活性处理组SOC和TN分别净增1.476、0.564 g·kg⁻¹，占总量32.4%、79.0%；灭活处理则分别为1.832、0.415 g·kg⁻¹，占比37.3%、73.5%。3）灭活处理粗颗粒态有机碳（CPOC）较对照增加111%，活性处理组细颗粒态（FPOC）和矿物结合态有机碳（MAOC）分别显著提升124%和153%。两处理组颗粒态总氮分别较对照提高533%和396%。4）第105天时活性与灭活处理表土叶绿素含量分别较初始增长142%和106%。5）微藻添加显著降低粉黏粒比例，活性与灭活处理使团聚体平均质量直径（MWD）分别增加10.3%和18.3%，活性组几何平均直径（GMD）提升10.8%。活性和灭活微藻通过光合固碳与生物固氮协同提升碳氮固持效率，促进团聚体形成、研究结果可为尾矿砂生态修复提供新途径。

关键词: 微藻, 稀土尾矿砂, 碳氮固持, 团聚体, 生态修复