Plant induced weathering of minerals in the subsoil - release of 'non-exchangeable' potassium from 2:1 layer minerals (TransMinK)

该提案探讨了底土对作物钾素营养的贡献潜力。更具体地说，我们将讨论控制K从2：1粘土矿物层间释放的过程，因为这预计是底土中的主要K组分。虽然过去的研究表明，这种所谓的“非交换性”K可以由于根系活动而释放，但对于触发这一过程所需的根际土壤溶液K浓度的作用，仍有争议的结果。同样，关于根际其他阳离子(NH4、Ca)的浓度动态及其对K释放和蠕虫化的影响的信息也很少，这被认为是与这一过程有关的。使用中央现场试验的底物的模型研究将在配备微型吸盘的隔室系统中进行。用X射线衍射仪、透射电子显微镜和扫描电子能谱研究土壤溶液组成随距离增加的动态变化与矿物学变化相结合。还将在中心田和中心微宇宙试验中采集大量土壤和根际样品，并在一个作物周期内露出矿物袋，研究由于植物诱导层间钾释放而导致的矿物学变化。最后，X射线CT将被用来了解土壤质地的变化，即根周围的粘土分布和根在生物孔中的时间扩散，这是从这种结构中吸收钾的先决条件。

The proposal addresses the potential of subsoil to contribute to K nutrition of crops. More specifically we will address the processes controlling release of K from interlayer of 2:1 clay minerals as this is expected to be the dominant K fraction in the subsoil. While it has been shown in the past that this so called “non-exchangeable” K can be released due to root activity, there are controversial results concerning the role of soil solution K concentration in the rhizosphere required to trigger the process. Likewise little information is available about the concentration dynamics of other cations (NH4, Ca) in the rhizosphere and their impact on K release and vermiculitization supposed to be associated with this process. Model studies with substrate from the central field trial will be conducted in compartment systems equipped with micro suction cups. The measurement of dynamic changes of soil solution composition with increasing distance from the root surface will be combined with investigations of changes in mineralogy by XRD, TEM and SEM-EDX. Changes of mineralogy as a result of plant induced K release from interlayer will also be studied on bulk soil and rhizosphere samples collected within the central field and the central microcosm experiment and with mineral bags exposed in the field during a cropping cycle. Finally, X-ray CT will be used to access changes in soil texture, i.e. clay distribution around roots and the temporal spread of roots in biopores which is a prerequisite for K uptake from such structures.