南湖新闻网讯（通讯员 彭珏）近日，我校资源与环境学院水土保持课题组在长期耕作下黑土团聚体孔隙结构和稳定性演变特征研究中取得新进展，相关成果以“Aggregate pore structure, stability characteristics, and biochemical properties induced by different cultivation durations in the Mollisol region of Northeast China”为题发表在Soil & Tillage Research上。
图1 长期耕作导致黑土团聚体孔隙结构变化和土壤退化机制示意图
常年强烈的机械化耕作使东北黑土有机碳和养分储量、总孔隙度和渗透能力均急剧降低，导致土壤质量退化，土地生产力显著下降。团聚体的数量、大小分布、周转速度及稳定性能够较好地反映土壤的结构状况，但其包涵的信息有限，尤其忽略了团聚体内部孔隙特征的差异，难以区分和判别各类土壤团聚体性状与特征，同时，从土壤孔隙结构角度联合土壤质量退化的研究仍需深入。基于此，课题组以我国东北农田黑土为研究对象，探讨黑土团聚体结构和稳定性对长期耕作的响应规律，构建土壤结构指数（SSI），旨在更优地阐明东北黑土土壤结构特征对耕地质量退化的响应机制。
图2 不同耕作年限黑土团聚体孔隙三维结构示意图
结果表明，随着耕作时间增加，团聚体平均质量直径逐渐降低，土壤有机碳、全氮和微生物生物量碳含量显著下降。黑土团聚体孔隙主要集中分布在团聚体中部区域，四周呈零散分布。总孔隙度和孔隙数量大体上随耕作时间的增加而减小。孔隙形态和孔径分布以细长型孔隙和> 100µm孔隙为主。与存在以大孔隙为中心发育的连通孔隙群的林地团聚体相比，耕地团聚体内部孔隙结构更为致密，出现更多的孤立小孔隙，孔隙多呈散点分布，表现出较差的连通性，这是由耕作过程中孔隙与孔隙之间的“通路”被人为破坏所致。根据综合各类结构性参数构建的SSI结果发现，开垦20年以上耕地的SSI普遍较低（大部分在0.4以下），且随耕作时间的增大而降低。由此，长期耕作导致土壤团聚体孔隙网络结构“简单化”、总孔隙度和连通性降低是土壤退化的重要原因。该研究对我国东北农田黑土质量退化特征机制提供了重要见解。
我校博士研究生彭珏为论文第一作者，王军光副教授为通讯作者。我校蔡崇法教授、中国科学院地理科学与资源研究所方海燕研究员、北京师范大学刘刚老师在实验设计和野外采样给予了指导。该研究得到了国家重点研发计划（2021YFD1500703）和国家自然科学基金（42177317）等项目的支持。
审核人 王军光
【英文摘要】
Long-term cultivation tends to cause thinning and even partial disappearance of Mollisols, which largely limits the sustainable development of agriculture. Cultivation duration greatly affects soil pore structure and biochemical properties of Mollisols. This study aims to elucidate the response of aggregate pore structure, stability, and biochemical properties of soil during degradation under long-term cultivation in Mollisols. The study involved four croplands with different cultivation durations (20, 40, 60, and 100 years; designated as AL20, AL40, AL60, and AL100, respectively) and one undisturbed forest land (FR). Samples were collected from three soil depths (0–20, 20–40, and 40–60 cm). Pore structure and biochemical properties were analyzed by X-ray Computed Tomography (CT) and standard method. As a result, the aggregate stability and biochemical properties of soil showed different degrees of degradation with the extension of cultivation duration. The mean weight diameter, soil organic carbon, total nitrogen, and microbial biomass carbon followed the order of AL20 > FR > AL40 > AL60 > AL100, while the soil bulk density exhibited an opposite trend. FR and AL20 showed significant differences from other sites (P < 0.05). The CT results revealed that total porosity and pore number approximately decreased with cultivation duration, with their maximum appearing in FR and minimum occurring in AL100. The pore shape and pore size of aggregates were dominated by elongated pores (> 65%) and porosity > 100 µm, respectively, both of which declined with increasing cultivation duration. Similarly, the fractal dimension and connectivity were the highest in FR. These results demonstrated that the pore structure of soil aggregates tended to be "simplified" with increasing cultivation duration. Soil structure index, which varied significantly with cultivation duration, was used to comprehensively evaluate the soil structure. The results provide important insights into soil structural degradation caused by long-term cultivation.
