Dynamics of Clay Fixed Potassium of Rhizosphere Soil Eco-System of Grasslands

1. 目的：研究了草地根际土壤中被粘土固定的钾离子比非根际土壤中的钾离子更容易被清除。据推测，这种关系是由草中渗出的有机酸的作用引起的。1)从草根中提取有机酸的鉴定与测定。2)测定层间蛭石钾与从根系渗出液中鉴定的有机酸反应的基间距。结果：1)钾层间蛭石基间距为1.0nm；经草根处理后，反应扩大到1.4nm，且随着草根数量的增加反应增强。2)根尖分泌物中存在许多已知和未知的有机酸。已知的有马来酸、柠檬酸、酒石酸、丙二酸、苹果酸、琥珀酸、乳酸、乙酸和丙酸。3)不同钾光照条件下根系渗出有机酸的含量不同，不同有机酸种类的根渗出部位也不同。4)经鉴定的已知有机酸（pH < 4）处理后，钾质层间蛭石基间距扩大至1.3nm。有机酸溶液中钾的含量从pH值4.3开始随pH值的降低呈指数增长。结论：阐明了根系分泌物中存在大量有机酸，它们作用于蛭石层间保持固定状态的速效钾，以速效钾的形式转移到土壤溶液中。

1. PURPOSE : It was found that the potassium fixed by clays in the rhizos-phere soil in a grassland was removed more easily than that of in the non-rhizosphere soil. It is supposed that the relationships was caused by the actions of organic acids exudated from the grasses. We investigated that 1) Identification and determination of rganic acids exdated from grass roots. 2) Measuring of basal spacings of potassium interlayered vermiculite reacted with organic acids identified from the grass root exudates.2. RESULTS : 1) The basal spacing of potassium interlayered vermiculite was 1.0nm. It expanded to 1.4nm after treatment with grass roots and the reaction increased with the numbers of grass roots. 2) There were many known and unknown organic acids in the exudates of root tips. The known ones were identified as maleic, citric, tartaric, malonic, malic, succinic, lactic, acetic and propionic acids. 3) The contents of the root-exudated organic acids were different by the conditions of potassium and light, and the sites of exudation were different accoding to the varieties of organic acids. 4) The basal spacing of potassium interlayered vermiculite expanded to 1.3nm after treatment with the identified known organic acids which pH were less than 4. The contents of potassium in the solution of organic acids began to increase exponentially with decrease of pH value from 4.3. CONCLUSION : It was clarified that there were many organic acids in the grass root exudates and they act on the less available potassium which was held in a fixed state in the interlayers of vermiculite to remove to the soil solution as an available potassium.