Identification of water flow through non-root soil macropores and along roots using X-ray computed tomography (CT) is still challenging because of limited methods to quantify roots and pore structures. This study selected shrub-encroached grassland consisting of a mosaic of shrub patches and interspace grass patches and the original grassland as a control treatment. Twelve intact soil columns (0–30 cm deep) were excavated, which included four replicates each from the soils under the original grassland, the shrub patches and interspace grass patches. Three-dimensional networks of soil macropores and roots were quantified using CT scanning and image analysis techniques, and active flow pathways were identified through KI tracing experiment using CT scanning. The results showed that the tracer depths of soils under the shrub patches and interspace grass patches were deeper than those of the original grassland, which was attributed to the well-developed root system. The tracer volume density was significantly and positively correlated with soil macropore node density and root volume density (p < 0.05), and significantly and negatively correlated with root mean angle (p < 0.05). Soils under the shrub patches had lower tracer volume density than that under the interspace grass patches, which was attributed to the horizontal-oriented roots under the shrub patches. The relative contribution of water flow along roots was larger than that through non-root soil macropores 35 min after dye application. This provided direct evidence that shrub roots were the main pathway of macropore flow resulting in water flow into deep soil layers in the shrub-encroached grassland.

中文翻译：

---

灌丛草地非根系土壤大孔隙和沿根系水流的识别

由于量化根和孔隙结构的方法有限，使用 X 射线计算机断层扫描 (CT) 识别通过非根土壤大孔和沿根的水流仍然具有挑战性。本研究选择由灌木斑块和间隙草斑块组成的灌木侵占草地和原始草地作为对照处理。挖掘了 12 个完整的土柱（0-30 厘米深），其中包括原始草地下的土壤、灌木斑块和间隙草斑块的四个重复。采用CT扫描和图像分析技术对土壤大孔隙和根系的三维网络进行量化，并通过CT扫描的KI示踪实验识别活跃的流动路径。结果表明，灌丛斑块和间隙草斑块下土壤示踪深度较原草地深，归因于根系发达。示踪体积密度与土壤大孔节点密度和根体积密度呈显着正相关（p  < 0.05），与均根角呈显着负相关（p  < 0.05）。灌木斑下的土壤示踪体积密度低于间隙草斑下的土壤，这归因于灌木斑下的水平定向根系。染料施用后35 min，沿根部的水流的相对贡献大于通过非根部土壤大孔的水流。这直接证明了灌木根系是大孔隙流动的主要途径，导致水流入灌木侵占草地的深层土壤。