Isolation and identification of allelochemicals in rhizosphere and adjacent soil under walnut (Juglans regia L.) trees
2012
Cui, Cui | Cai, Jing | Jiang, Zaimin | Zhang, Shuoxin
The mechanism of allelopathic effects in the rhizosphere soil of walnut (Juglans regia L.) trees was investigated. To identify the allelochemicals present in the rhizosphere soil, the rhizosphere and adjacent soil beneath walnut trees was extracted using 20% methanol, methanol, ethyl acetate and hexane. The effects of these extracts (20% methanol, methanol, ethyl acetate and n-hexane) from the rhizosphere and adjacent soil were investigated separately on the seed germination and seedling growth of cabbage (Brassica oleracea L. var. capitata L). All these extracts inhibited the seed germination and the length of cabbage seedlings than control (soil adjacent to walnut trees). This indicated the presence of compounds in the rhizosphere soil of walnut trees with allelopathic effects on cabbage, presumably derived from the root exudates of walnut trees. Many compounds were identified in these four extracts of walnut tree rhizosphere soil and these compounds were different from those found in the adjacent soil. The extractions with different polarity solvents showed that n-Hexadecanoic acid, 9,12-octadecadienoic acid (Z,Z), 8-Octadecenoic acid and 5-hydroxy-1,4-naphthoquinone may also be important allelochemical components in walnut tree rhizosphere soil. Based on these data, we concluded that the compounds identified in the rhizosphere soil of walnut trees using different polarity extracts provided a comprehensive evaluation of the allelopathic compounds present.
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