Key Laboratory of Mollisols Agroecology, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun 130102, China; University of Chinese Academy of Sciences, Beijing 100049, China.
College of Environmental Science and Engineering, Zhongkai University of Agriculture and Engineering, Guangzhou 510225, China.
Sci Total Environ. 2020 Feb 10;703:134617. doi: 10.1016/j.scitotenv.2019.134617. Epub 2019 Nov 2.
Soil structure plays a key role in soil organic carbon (SOC) dynamics. To determine how soil structure and aggregate affects SOC, we collected undisturbed soil cores of 0-5 cm layer (Typic Hapludoll) at an experimental site in Northeast China. The site had been under continuous tillage treatments of conventional tillage (CT) and no tillage (NT) for 17 years. We measured SOC by elemental analysis, aggregate size distribution by wet sieving, and soil pore parameters of pore size distribution, pore average diameter, pore numbers, pore connectivity, pore anisotropy, and pore fractal dimension by X-ray computer tomography. SOC content was significantly correlated with aggregate-associated SOC and soil water-stable aggregate content. CT with residue removal and annual plowing and cultivation increased <53 μm and 53-250 μm aggregates. CT decreased total SOC of 0-5 cm soil layer but increased aggregate-associated SOC of <53 μm. NT with greater residue input increased total SOC of 0-5 cm soil layer by 26.0% and aggregate mean weight diameter by 111.8% and increased aggregates of 250-1000 μm and >1000 μm. Soil under NT had a greater total number of micropores and greater connectivity whereas CT had a greater total number of macropores, average macropore diameter, anisotropy, and fractal dimension. Structural equation modeling showed that CT can decrease SOC of 0-5 cm soil layer by different paths, including increased anisotropy and macropore porosity, and NT can increase SOC of 0-5 cm soil layer by different paths, including increased mean weight diameter and connectivity. These results enhance our understanding of the relationship between soil structure and SOC, and could guide tillage management decisions to increase SOC.
土壤结构在土壤有机碳（SOC）动态中起着关键作用。为了确定土壤结构和团聚体如何影响 SOC，我们在中国东北地区的一个实验点采集了未扰动的 0-5cm 土层（典型的均腐殖质土）土壤芯。该实验点连续 17 年采用传统耕作（CT）和免耕（NT）处理。我们通过元素分析测量 SOC，通过湿筛法测量团聚体大小分布，通过 X 射线计算机断层扫描测量土壤孔隙参数，包括孔径分布、平均孔径、孔隙数、孔隙连通性、孔隙各向异性和孔隙分形维数。SOC 含量与团聚体相关 SOC 和土壤水稳性团聚体含量显著相关。去除残茬并进行年度耕翻和耕作的 CT 增加了<53μm 和 53-250μm 团聚体。CT 降低了 0-5cm 土层的总 SOC，但增加了<53μm 的团聚体相关 SOC。具有更大残茬输入的 NT 增加了 0-5cm 土层的总 SOC 26.0%，团聚体平均重量直径增加了 111.8%，并增加了 250-1000μm 和>1000μm 的团聚体。NT 下的土壤具有更大的总微孔数量和更大的连通性，而 CT 下的土壤具有更大的总大孔数量、平均大孔直径、各向异性和分形维数。结构方程模型表明，CT 可以通过不同的途径降低 0-5cm 土层的 SOC，包括增加各向异性和大孔孔隙度，NT 可以通过不同的途径增加 0-5cm 土层的 SOC，包括增加平均重量直径和连通性。这些结果增强了我们对土壤结构与 SOC 之间关系的理解，并可为增加 SOC 提供耕作管理决策的指导。
