| Walnut (Juglans regia L.), which is planted in a wide range in China, is one of the typical allelopathic trees in economic forest species. In order to take full advantage of economic benefits of walnut and improve resource utilization of agricultural production, intercropping of walnut and other crops has become a trend. However, during long-term growth and development, walnut forms some allelochemicals to affect the growth of neighboring crops. Therefore, allelopathic effects of root extracts, root exudates, rhizosphere and non-rhizosphere soil extracts of walnut were measured in this study, the allelopathic mechanism was also preliminary investigated to provide theoretical evidence for comprehensive research of allelochemicals source and allelopathic mechanism. The main findings were as follows:(1) Allelochemicals of walnut root were extracted by different solvents and methods, and allelopathic activities of them were valued by the indicator of synthesis effect. The results showed that95%ethanol cold soak extract had the strongest inhibition on the seed germination and seedling growth of wheat, cabbage and mung bean.(2) Allelopathy of different extract phases and aqueous phase of alcohol extracts from walnut root were measured. The results showed that when the tested concentration was40mg-mL-1, the SE of ethyl acetate extracts was the strongest one, and inhibited effect on root growth of wheat and cabbage was stronger than inhibited effect on seelding growth. As the increasing of extracts concentration, there was a significant increase in inhibited effect on root length and seedling height of wheat. However, allelopathic effect on root length and seedling height of cabbage and mung bean presented dual effects; low concentration promoted growth, while high concentration inhibited growth. Ethyl acetate extract phase of alcohol extracts from walnut root has more, or more stable, or more active allelochemicals.(3) After treated by different concentrations of ethyl acetate extracts, the activity of SOD showed a trend that firstly increased and then decreased with extracts concentration increasing. Meanwhile, the activity of POD decreased; the content of MDA increased; the soluble protein content firstly increasd and then decreased, at last increased. Defense enzyme system and structure of cell membrane of acceptor were broken by allelochemicals.(4) Active tracking means was adopted to preliminary separate allelochemicals from ethyl acetate extract phase through column chromatography. Fr4had the strongest inhibited effect on seed germination, root length and seedling height of wheat. After further separation, inhibitory rate of Fr4-5and Fr4-6to seed germination, root length and seedling height of wheat reached100%.(5) Sand culture and hydroponic culture method were adopted to collect root exudates. The amounts of sand culture were more than that of hydroponic culture. Inhibited effect on seed germination of root exudates of hydroponic culture was greater than that of sand culture. Within the tested concentrations, root exudates of sand culture all had inhibited effect on root length and seedling height of wheat; however, for hydroponic culture, low concentration promoted growth, while high concentration inhibited growth. Evaluation of synthesis effect showed that inhibited effect of root exudates of sand cultrue on wheat growth is stronger than inhibited effect of hydroponic culture.(6) Effects of root exudates from sand cultrue on the characteristics of physiological and biochemical of wheat is greater. Within the tested concentrations, root exudates of two collection methods all inhibited the growth of wheat and broken normal metabolic levels. With concentration of root exudates increasing, the activity of SOD and POD showed a trend that firstly increased and then decreased; the content of MDA increased. The soluble protein content of wheat that was treated by sand culture root exudates decreased, but firstly increasd and then decreased when wheat was treated by hydroponic culture root exudates.(7) Allelopathy of rhizosphere and non-rhizosphere soil extracts of walnut from HL and SY were measured. For inhibited effect on wheat growth, rhizosphere soil extracts had more impact than non-rhizosphere soil extracts; soil extracts from HL had more impact than that from SY. With extracts concentration increasing, inhibited effects on seed germination, root length, seedling height and relative water content of wheat increased. Inhibited effect of rhizosphere and non-rhizosphere soil collected within the vertical drip line of walnut tree crown on wheat growth was stronger than that of soil collected out of vertical drip line. Wheat growth was hardly affected by soil which had been collected away from walnut root. It is better to plant intercropping species outside the vertical drip line of walnut tree crown. In this way, allelopathy of walnut root and leaching materials from branches and leaves will have no effect on plant growth condition and crop output. |
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