Institute of Soil Science, Leibniz Universität Hannover, Herrenhäuser Str. 2, 30419 Hannover, Germany.
Soil Science and Soil Protection, Martin Luther University Halle-Wittenberg, Von-Seckendorff-Platz 3, 06120 Halle (Saale), Germany.
Sci Rep. 2017 Feb 17;7:42877. doi: 10.1038/srep42877.
Soil wettability (quantified in terms of contact angle, CA) is crucial for physical, chemical, and biological soil functioning. As the CA is determined by components present within the outmost nanometer of particles, this study applied X-ray photoelectron spectroscopy (XPS) with a maximum analysis depth of 10 nm to test the relationship between CA and surface elemental composition, using soil samples from a chronosequence where CA increased from 0° (0 yrs) to about 98° (120 yrs). Concurrently, as seen by XPS, C and N content increased and the content of O and the mineral-derived cations (Si, Al, K, Na, Ca, Mg, Fe) decreased. The C content was positively correlated with CA and least squares fitting indicated increasing amounts of non-polar C species with soil age. The contents of O and the mineral-derived cations were negatively correlated with CA, suggesting an increasing organic coating of the minerals that progressively masked the underlying mineral phase. The atomic O/C ratio was found to show a close negative relationship with CA, which applied as well to further sample sets of different texture and origin. This suggests the surface O/C ratio to be a general parameter linking surface wettability and surface elemental composition.
土壤润湿性（以接触角 CA 来量化）对土壤的物理、化学和生物功能至关重要。由于 CA 是由颗粒最外层存在的成分决定的，因此本研究采用 X 射线光电子能谱（XPS），其最大分析深度为 10nm，以测试 CA 与表面元素组成之间的关系，所用土壤样本取自一个时间序列，其中 CA 从 0°（0 年）增加到约 98°（120 年）。同时，如 XPS 所见，C 和 N 含量增加，而 O 和矿物衍生阳离子（Si、Al、K、Na、Ca、Mg、Fe）的含量减少。C 含量与 CA 呈正相关，最小二乘法拟合表明，随着土壤年龄的增加，非极性 C 物质的含量增加。O 和矿物衍生阳离子的含量与 CA 呈负相关，表明矿物表面逐渐被有机物质覆盖，从而掩盖了潜在的矿物相。发现原子 O/C 比与 CA 呈密切负相关，这同样适用于不同质地和来源的进一步样本集。这表明表面 O/C 比是一个将表面润湿性和表面元素组成联系起来的通用参数。
