ABSTRACT

Potassium (K) fertilizers have been widely used to promise agricultural production, yet rice (Oryza sativa L.) showed healthy growth for long periods under K-deficient conditions. These findings imply that rice could take up minerals-bound K as non-exchangeable K. When the weathering of primary silicate minerals occurs in the rhizosphere of rice, the rice takes up not only dissolved K but also dissolved silicic acid (SiO₂). We grew three rice cultivars with different Si-uptake abilities (Hokuriku 193, Oochikara, and Lsi-1) in granitic Fluvisol under K- and Si-deficient conditions to quantitatively reveal the significance of the Si-uptake by rice for the mineral weathering in the rhizosphere. As a result, the Si-uptake quantity by rice was positive linearly correlated with the amount of Al accumulation in soil, suggesting a substance containing a certain ratio of Si and Al was decomposed by rice. The K:Al:Si molar ratio of the decomposed substance by rice was 0.2:1:2.6, and the ratio is suggestive of silicate minerals such as K-feldspar. Because silicate minerals such as K-feldspar (e.g., KAlSi₃O₈) contain a large amount of aluminum (Al), Al release alongside K ions and silicic acid in their weathering. Dissolved Al is highly active and can be stabilized by combining with organic matter (OM) or silicic acid in the rhizosphere. The Si-uptake levels and mineral decomposing abilities of rice affected the variety of the accumulated substances (i.e., Al hydroxy oxide with OM, clay minerals) in the soil after cultivation. In particular, the Al hydroxy oxide with OM accumulates as persistent soil organic carbon. Thus, it appears that the Si-uptake abilities of plants have a great influence on the weathering of minerals and their products.

摘要

钾 (K) 肥料已广泛用于保证农业生产，但水稻 ( Oryza sativa L.) 在缺钾条件下长期健康生长。这些发现意味着水稻可以吸收矿物质结合的钾作为不可交换的钾。当水稻根际原生硅酸盐矿物风化时，水稻不仅吸收溶解的钾，而且吸收溶解的硅酸（SiO ₂）。我们种植了三种具有不同 Si 吸收能力的水稻品种（Hokuriku 193、Oochikara 和Lsi-1) 在缺钾和缺硅条件下的花岗岩 Fluisol 中，定量揭示水稻吸收硅对根际矿物风化的重要性。结果表明，水稻对硅的吸收量与土壤中铝的积累量呈正线性相关，表明含有一定比例硅铝的物质被水稻分解。大米分解物的K:Al:Si摩尔比为0.2:1:2.6，该比例提示钾长石等硅酸盐矿物。由于硅酸盐矿物，如钾长石（如 KAlSi ₃ O ₈) 含有大量的铝 (Al)，Al 在风化过程中与 K 离子和硅酸一起释放。溶解铝具有高活性，可以通过与根际中的有机物 (OM) 或硅酸结合来稳定。水稻对硅的吸收水平和矿物质分解能力影响栽培后土壤中积累物质（即含有机质的羟基氧化铝、粘土矿物）的种类。特别是，含 OM 的羟基氧化铝以持久性土壤有机碳的形式积累。因此，植物对硅的吸收能力似乎对矿物及其产物的风化有很大影响。