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

1.目得：结果表明，草地根际土壤中粘粒固定的钾素比非根际土壤中的钾素更容易被迁移。推测这种关系是由牧草分泌的有机酸的作用引起的。研究了1）从植物根中提取有机酸的鉴定与测定。2)测定了有机酸与钾基蛭石层间距的关系.结果：1）钾层间蛭石的层间距为1.0nm。经草根处理后，其荧光强度可达1.4nm，且随着草根数量的增加，荧光强度增强。2)根尖分泌物中含有多种已知和未知的有机酸。已知的酸被鉴定为马来酸、柠檬酸、酒石酸、丙二酸、苹果酸、琥珀酸、乳酸、乙酸和丙酸。3)根系分泌的有机酸含量因钾、光条件不同而不同，分泌部位因有机酸种类不同而不同。4)钾层间蛭石经pH小于4的已知有机酸处理后，层间距扩大到1.3nm。有机酸溶液中钾的含量从pH 4.3开始随pH值的降低呈指数增加。结论：结果表明，根系分泌物中含有大量的有机酸，有机酸作用于蛭石层间固定的速效钾，使其以速效钾的形式进入土壤溶液。

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.