Rhizosphere soil is known to differ from the bulk soil due to numerous physicochemical processes induced by root growth. The spatial extent and magnitude of the influence of roots on the surrounding soil is still debated controversially. To date, most studies focused on a limited number of soil types and plant species and were carried out under homogeneous soil structure conditions (i.e., finely sieved and repacked soil). With the help of X-ray computed tomography (CT), we present the results of an image processing workflow, which enabled to analyze soil structure around roots of maize (Zea mays L.) plants under different degrees of soil structure heterogeneity. We analyzed >400 samples extracted during laboratory and field experiments covering various combinations of texture, bulk density, packing heterogeneity, maize genotype, and soil moisture. We show that soil texture and structure heterogeneity predominantly governs the magnitude of bulk density alteration around roots. In homogeneous soil structure, roots had to create their own pores by pushing away soil particles, which confirms previous findings. Under more heterogeneous conditions, we found that roots predominantly grew in existing pores without inducing compaction. The influence of root hairs, root length density, and plant growth stages had no or little impact on the results. The effect of root diameter was more pronounced in sand than in loam. Fine roots caused sand grains to align along their axis, whereas big roots broke the fragile arrangement of grains. Our findings have implications for water and solute transport dynamics at the root–soil interface, which may affect plant productivity.

中文翻译：

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土壤质地和结构异质性主要控制根部周围的体积密度梯度

由于根系生长引起的许多物理化学过程，根际土壤与大块土壤不同。根系对周围土壤影响的空间范围和大小仍存在争议。迄今为止，大多数研究都集中在数量有限的土壤类型和植物物种上，并且是在均质土壤结构条件下（即细筛和重新填充的土壤）进行的。在 X 射线计算机断层扫描 (CT) 的帮助下，我们展示了图像处理工作流程的结果，该工作流程能够分析玉米 ( Zea mays)根部周围的土壤结构L.) 不同程度土壤结构异质性下的植物。我们分析了在实验室和田间实验中提取的 400 多个样本，涵盖了质地、堆积密度、包装异质性、玉米基因型和土壤水分的各种组合。我们表明土壤质地和结构异质性主要控制根部周围体积密度变化的幅度。在均质的土壤结构中，根部必须通过推开土壤颗粒来产生自己的孔隙，这证实了之前的发现。在更异质的条件下，我们发现根主要在现有孔隙中生长而不会引起压实。根毛、根长密度和植物生长阶段的影响对结果没有影响或影响很小。根直径的影响在沙土中比在壤土中更显着。细根使沙粒沿轴线排列，而大根破坏了沙粒的脆弱排列。我们的研究结果对根 - 土壤界面处的水和溶质运输动力学有影响，这可能会影响植物生产力。