Root exudates alter the rhizosphere's physical properties, but the impact that these changes have on solute transport is unknown. In this study, we tested the effects of chia mucilage and wheat root exudates (WREs) on the transport of iodide and potassium in saturated or unsaturated soil. Saturated solute breakthrough experiments, conducted in loamy sand soil or coarser textured quartz sand, revealed that increasing the exudate concentration in soil resulted in non-equilibrium solute transport. This behavior was demonstrated by an initial solute breakthrough after fewer pore volumes (PVs) and the arrival of the peak solute concentration after greater PVs in soil mixed with exudates compared to soil without exudates. These patterns were more pronounced for the coarser textured quartz sand than for the loamy sand soil, and in soil mixed with mucilage than in soil mixed WREs. Parameter fits to these breakthrough curves with a mobile-immobile transport model indicated the fraction of immobile water increased as the concentration of exudates increased. For example, in quartz sand the estimated immobile fraction increased from 0 without exudates to 0.75 at a mucilage concentration of 0.2%. The solutes' breakthrough under unsaturated conditions was also altered by the exudates, demonstrated by a smaller volume of water extracted from soil mixed with exudates, compared to soil without exudates, before the arrival of the peak solute concentration. The results indicate that exudates alter the rhizosphere's transport properties; we hypothesize that this is due to exudates creating low-conducting flow paths that result in a physical non-equilibrium solute transport.

中文翻译：

---

根系分泌物改变土壤中的养分运输

根系分泌物改变了根际的物理特性，但这些变化对溶质运输的影响尚不清楚。在这项研究中，我们测试了奇亚籽粘液和小麦根系分泌物 (WRE) 对饱和或不饱和土壤中碘化物和钾的运输的影响。在壤质砂土或质地较粗的石英砂中进行的饱和溶质突破实验表明，增加土壤中渗出物浓度会导致非平衡溶质迁移。与没有渗出物的土壤相比，在与渗出物混合的土壤中，在较小的孔隙体积 (PV) 后初始溶质突破和在更大的 PVs 之后达到峰值溶质浓度证明了这种行为。质地较粗糙的石英砂的这些图案比壤质砂土更明显，并且在与粘液混合的土壤中比在土壤混合 WRE 中。使用移动-固定传输模型拟合这些突破曲线的参数表明，固定水的比例随着渗出液浓度的增加而增加。例如，在石英砂中，在粘液浓度为 0.2% 时，估计的固定分数从没有渗出物的 0 增加到 0.75。渗出液也改变了不饱和条件下溶质的突破，这表明在溶质浓度达到峰值之前，与没有渗出液的土壤相比，从混有渗出液的土壤中提取的水量更小。结果表明，渗出物改变了根际的运输特性；