Andosol genesis: Transition from silandic to aluandic properties and the related changes for organic carbon storage.

安多索土细分为硅质安多索土和硅质安多索土，它们通常被视为安多索土成因的端元。硅兰期安多斯土主要由OM和类莫来石相形成的有机-矿物组合组成，包括尿磷矿、蒙脱石和原蒙脱石。Al-OM络合物(Al-OM络合物)主要由Al-OM络合物组成。在这两个亚组中，结果是有机质和土壤矿物质基质的密切联系。目前的理论认为，硅质和金红石性质是原生风化的直接结果，即来自两种不同的成壤作用。然而，我们自己以前的研究表明，随着时间的推移，具有硅质性质的层位可能会转变为具有银质性质的层位。我们认为，这是由于酸性溶解有机物(DOM)随渗水进入下层土壤，导致拟沸石类相溶解，释放铝所致。释放的铝和DOM立即形成Al-OM络合物，因此，拟议的工作旨在验证这一假说并确定影响这一过程的因素。我们将研究一种单层厄瓜多尔安多索尔，其表土以银质为主，下层以硅质为主。首先，我们将通过进行吸附批次实验来确定底土和表土是否饱和了OM。然后，我们将使用酸性DOM溶液(模拟石型相溶解的pH)在渗流实验中监测从硅酸盐到铝酸盐的原位转变。我们将结合不同的技术跟踪矿物相的变化。由于土样的短程有序和纳米或微晶性质，伊莫高石型相以及Al-OM复合体在表征和定量方面具有挑战性。此外，它们往往彼此密切相关。为了对它们进行定量化和定量化，我们将结合使用密度分馏、化学提取和显微镜(结合元素检测的透射电子显微镜)和现代光谱技术(傅立叶变换红外光谱、X射线光电子能谱、同步加速器Al K边X射线吸收光谱)，以期对安多索的成因以及短程有序矿物相的形成和转化有新的认识。这些矿物相对安多斯土和其他土壤中有机质的积累和储存起着关键作用。

Andosols are subdivided in silandic and aluandic Andosols, which are often seen as endmembers of the Andosols genesis. Silandic Andosols mainly consist of organic‒mineral associations formed by OM and imogolite-type phases, including allophanes, imogolites, and protoimogolites. Aluandic Andosols consist mainly of aluminium‒OM complexes (Al‒OM complexes). In both subgroups the result is an intimate association of OM and the soil mineral matrix. The current theory is that silandic and aluandic properties are direct results of primary weathering, i.e., result from two different lines of pedogenesis.Our own previous investigations, however, suggest that horizons with silandic properties may transform to horizons with aluandic properties over time. We think that this is caused by acidic dissolved organic matter (DOM) entering the subsoil with the percolating water, causing dissolution of the imogolite-type phases and releasing aluminium. The released aluminium and DOM instantly form into Al‒OM complexes.Thus, the proposed work aims at testing this hypothesis and determining the factors influencing that process. We will study a one-layered Ecuadorian Andosol, with pre-dominating aluandic properties in the topsoil and pre-dominating silandic properties in the subsoil. First, we are going to determine if the sub- and topsoils are saturated with OM by performing sorption batch experiments. Then, the in situ transformation from silandic to aluandic properties will be monitored in a percolation experiment, using an acidic DOM solution (pH at which imogolite-type phases dissolve).We will track changes of the mineral phase with a combination of different techniques. Imogolite-type phases as well as Al‒OM complexes are challenging to characterize and quantify in soil samples due to their short range-ordered and nano- or micro-crystalline nature. Also, they are often closely associated with each other. In order to characterize and quantify them, we will apply a combination of density fractionation, chemical extractions and microscopy (transmission electron microscopy in combination with element detection) as well as modern spectroscopic techniques (Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, synchrotron-based Al K-edge X-ray absorption spectroscopy).We expect to gain new insights into the genesis of Andosols, as well as on the formation and transformation of short range-ordered mineral phases. These mineral phases play a key role for accumulating and storing organic matter in Andosols and other soils.