Research Group of Soil Fertility and Nutrient Management, Department of Environment, Ghent University, Coupure Links 653, 9000, Gent, Belgium.
British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK.
Sci Rep. 2021 Jan 11;11(1):370. doi: 10.1038/s41598-020-79681-5.
Degradability of organic matter (OM) in soil depends on its spatial location in the soil matrix. A recent breakthrough in 3D-localization of OM combined dual-energy X-ray CT-scanning with OsO staining of OM. The necessity for synchrotron-based µCT and the use of highly toxic OsO severely limit applications in soil biological experiments. Here, we evaluated the potential of alternative staining agents (silver nitrate, phosphomolybdenic acid (PMA), lead nitrate, lead acetate) to selectively enhance X-ray attenuation and contrast of OM in CT volumes of soils containing specific mineral soil particle fractions, obtained via lab-based X-ray µCT. In comparison with OsO, administration of Ag and Pb resulted in insufficient contrast enhancement of OM versus fine silt (< 20 µm) or clay (< 2 µm) mineral particles. The perfusion procedure used in this work induced changes in soil structure. In contrast, PMA staining resulted in a selective increase of OM's attenuation contrast, which was comparable to OsO. However, OM discrimination from other soil phases remained a challenge. Further development of segmentation algorithms accounting for grey value patterns and shape of stained particulate OM may enable its automated identification. If successful in undisturbed soils, PMA staining may form an alternative to OsO in non-synchrotron based POM detection.
土壤中有机质（OM）的降解性取决于其在土壤基质中的空间位置。最近在 OM 的三维定位方面取得了突破，将双能 X 射线 CT 扫描与 OM 的 OsO 染色相结合。基于同步加速器的 µCT 的必要性和使用剧毒的 OsO 严重限制了其在土壤生物学实验中的应用。在这里，我们评估了替代染色剂（硝酸银、磷钼酸（PMA）、硝酸铅、乙酸铅）的潜力，以选择性增强含有特定矿物土壤颗粒分数的土壤 CT 体积中 OM 的 X 射线衰减和对比度，这些分数是通过基于实验室的 X 射线 µCT 获得的。与 OsO 相比，Ag 和 Pb 的给药导致 OM 对细粉（<20 µm）或粘土（<2 µm）矿物颗粒的对比度增强不足。本工作中使用的灌注程序会引起土壤结构的变化。相比之下，PMA 染色导致 OM 的衰减对比度选择性增加，与 OsO 相当。然而，OM 与其他土壤相的区分仍然是一个挑战。进一步开发考虑染色颗粒状 OM 的灰度值模式和形状的分割算法，可能使其能够自动识别。如果在未扰动的土壤中成功，PMA 染色可能成为基于非同步加速器的 POM 检测中 OsO 的替代方法。
