Bioengineering Sciences Research Group, Faculty of Engineering and Physical Sciences, School of Engineering Sciences, University of Southampton, Southampton, SO17 1BJ, UK.
Paul Scherrer Institute, Swiss Light Source, Villigen, 5232, Switzerland.
New Phytol. 2020 Feb;225(4):1476-1490. doi: 10.1111/nph.16242. Epub 2019 Nov 12.
Rhizosphere soil has distinct physical and chemical properties from bulk soil. However, besides root-induced physical changes, chemical changes have not been extensively measured in situ on the pore scale. In this study, we couple structural information, previously obtained using synchrotron X-ray computed tomography (XCT), with synchrotron X-ray fluorescence microscopy (XRF) and X-ray absorption near-edge structure (XANES) to unravel chemical changes induced by plant roots. Our results suggest that iron (Fe) and sulfur (S) increase notably in the direct vicinity of the root via solubilization and microbial activity. XANES further shows that Fe is slightly reduced, S is increasingly transformed into sulfate (SO ) and phosphorus (P) is increasingly adsorbed to humic substances in this enrichment zone. In addition, the ferrihydrite fraction decreases drastically, suggesting the preferential dissolution and the formation of more stable Fe oxides. Additionally, the increased transformation of organic S to sulfate indicates that the microbial activity in this zone is increased. These changes in soil chemistry correspond to the soil compaction zone as previously measured via XCT. The fact that these changes are colocated near the root and the compaction zone suggests that decreased permeability as a result of soil structural changes acts as a barrier creating a zone with increased rhizosphere chemical interactions via surface-mediated processes, microbial activity and acidification.
根际土壤的物理和化学性质与体相土壤明显不同。然而，除了根系诱导的物理变化外，在孔隙尺度上原位广泛测量化学变化尚未得到广泛研究。在这项研究中，我们将先前使用同步加速器 X 射线计算机断层扫描（XCT）获得的结构信息与同步加速器 X 射线荧光显微镜（XRF）和 X 射线吸收近边结构（XANES）相结合，以揭示植物根系诱导的化学变化。我们的结果表明，通过溶解和微生物活动，铁（Fe）和硫（S）在根的直接附近显著增加。XANES 进一步表明，Fe 略有还原，S 越来越多地转化为硫酸盐（SO ），P 越来越多地被吸附到富里酸物质中，在这个富化区。此外，水铁矿分数急剧下降，表明优先溶解和形成更稳定的 Fe 氧化物。此外，有机 S 向硫酸盐的转化增加表明该区域的微生物活性增加。这些土壤化学变化与之前通过 XCT 测量的土壤压实区相对应。这些变化与根和压实区相邻的事实表明，由于土壤结构变化导致的渗透率降低会形成一个通过表面介导的过程、微生物活性和酸化增加根际化学相互作用的区域。
