Topsoil hardening is one of the major causes of poor root growth although its effects on subsoil roots are still not well-known. Our aim was to examine the effects of topsoil hardening on the growth and functioning of shallow and deep roots of soybean plants. Two rain shelter experiments were conducted in two consecutive years. Plants were grown in topsoil monoliths (0–20 cm) with low (LR) or high mechanical resistance (HR), extracted from adjacent no-tillage cropping fields, and placed above 180 cm-high containers filled with a sandy loam soil. The effects of topsoil hardening were largely regulated by the level of water stress. In stressed plants, HR conditions reduced total aboveground biomass (up to 13%), total root biomass, root length density, and root surface area (up to 23, 38, and 37% respectively). Mechanical impedances reduced root biomass and length in both shallow (0–20 cm) and very deep layers (+ 160 cm). No changes were observed in specific root length or specific surface area. Plants growing in HR topsoils showed lower total water extraction but greater specific water uptake rates (29–47% higher in year 1 and 2 respectively). No clear architectural (i.e., root density) or morphological (i.e., specific root length/area) responses of enhanced root foraging capacity were observed in subsoil roots. However, soybean root system responded through functional mechanisms (i.e., specific water uptake) which partially attenuated the negative effects of mechanical impedances.

中文翻译：

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表土硬化：对大豆根系结构和水分提取模式的影响

表土硬化是根系生长不良的主要原因之一，尽管其对底土根系的影响仍不为人所知。我们的目的是检查表土硬化对大豆植物浅根和深根的生长和功能的影响。连续两年进行了两次避雨实验。植物生长在具有低 (LR) 或高机械阻力 (HR) 的表土整块（0-20 厘米）中，从相邻的免耕农田中提取，并放置在 180 厘米高的容器上方，容器中装有沙壤土。表土硬化的影响在很大程度上受水分胁迫水平的调节。在受胁迫的植物中，HR 条件降低了总地上生物量（高达 13%）、总根生物量、根长密度和根表面积（分别高达 23%、38% 和 37%）。机械阻抗降低了浅层（0-20 厘米）和非常深层（+ 160 厘米）的根生物量和长度。在比根长或比表面积方面没有观察到变化。在 HR 表土中生长的植物显示出较低的总水提取量，但比吸水率更高（第 1 年和第 2 年分别高出 29-47%）。在底土根系中没有观察到明显的结构（即根密度）或形态（即特定的根长/面积）响应增强的根觅食能力。然而，大豆根系通过功能机制（即特定吸水量）作出反应，部分减弱了机械阻抗的负面影响。在 HR 表土中生长的植物显示出较低的总水提取量，但比吸水率更高（第 1 年和第 2 年分别高出 29-47%）。在底土根系中没有观察到明显的结构（即根密度）或形态（即特定的根长/面积）响应增强的根觅食能力。然而，大豆根系通过功能机制（即特定吸水量）作出反应，部分减弱了机械阻抗的负面影响。在 HR 表土中生长的植物显示出较低的总水提取量，但比吸水率更高（第 1 年和第 2 年分别高出 29-47%）。在底土根中没有观察到明显的结构（即根密度）或形态（即特定的根长度/面积）响应增强的根觅食能力。然而，大豆根系通过功能机制（即特定吸水量）作出反应，这部分减弱了机械阻抗的负面影响。