| Allelopathy is one of the most important chemoecological phenomena, which refersto one plant (donor) impact the growth and development on its neighboring plants (accepter)through the release of secondary metabolism chemical compounds into the environment viavolatilization, leaching, excretion, and decomposition. Walnut (Juglans regia L.) is awidespread tree in walnut genus (Juglans) of walnut family (Juglamdacea). It is plantedoriginally for a long history in China. However, all of the foliage, root and fruit peel of walnutcan inhibit the growth of neighbor plants signigicantly. In this study, bioassay methods wereused to probe into the walnut allelopathic effect on receiver plants, and chemical componentswere analyzed and identified with gas chromatograph-mass spectrometer (GC-MS), therhizosphere soil extracting effects with different solvents,root exudates extracts of walnuttrees, and the effect of root exudates on rhizosphere soil microecology were studied to providea scientific basis and the theoretical basis for optimizing the practice of the economic modelfor agroforestry systems in the loess area of nothern Wei River. The results showed:1. Walnut leaf aqueous extract affected the seed germination and seedling growth offritillaria, wheat, turnip, peanut, mung bean, and cabbage, showing significant allelopathiceffect and concentration effect. Receiver plants for further study were selected, which wereturnip and cabbage.2. The rhizosphere soil of walnut trees was extracted with different solvents (20%methanol, methanol, ethyl acetate, and n-hexane). Bioassay methods were used to probe intothe four different extracts of walnut trees rhizosphere soil, which showed the significantallelopathic effect. Totally12sorts91components were identified from the rhizosphere soilof2-year-old walnut trees, which included esters, alcohols, alkanes, olefins, ketones,aldehydes, naphthalenes, acids, phenols, amides, benzene, and quinones; totally11sorts90components were identified from the rhizosphere soil of3-year-old walnut trees, whichincluded alkanes, olefins, alcohols, acids, esters, aldehydes, ketones, phenols, and amides;totally14sorts89components were identified from the rhizosphere soil of4-year-old walnuttrees, which included alkanes, olefins, alcohols, acids, esters, ketones, phenols, aldehydes, quinones, benzene rings, aromatic hydrocarbons, cyanogens, benzenes.3. Root exudates extracts of walnut trees in different ages all showed the significantallelopathic effect. Totally9sorts35components were identified from the root exudates of2-year-old walnut trees, which included alkanes, olefins, alcohols, acids, esters, amides,phenols, quinones, benzenes; totally10sorts43components were identified from the rootexudates of3-year-old walnut trees, which included alkanes, alcohols, acids, esters, amides,ketones, phenols, quinones, olefins, and aldehydes; totally9sorts50components wereidentified from the root exudates of4-year-old walnut trees, which included alkanes, alcohols,acids, esters, amines, phenols, olefins, quinones, aromatic hydrocarbons.4. In the growth process of walnut trees, the contents of organic and inorganic nutrientsin rhizosphere soil were basically higher than those in bulk soil and the contents of organicmatter, total N, available N, total K, and available K increased with the age increasing; total Pand available P content and pH value reduced with the age increasing, and excepting the pHvalue significantly increased with the increase of soil depth, obviously decreased with theincrease of soil depth. Compared to bulk soil, the catalase, urease, phosphatase and sucraseactivities in rhizosphere soil of walnut trees decreased and activities of the four enzymesdecreased with the depth of spatial profile, indicated that the soil enzymes activities may berelated with the root secretion. Urease and sucrase activities in rhizosphere soil increased withthe ages of walnut trees; phosphatase activities decreased with the ages of walnut trees. In therhizosphere soil of walnut trees in different ages, variation rules of different soil enzymeactivities were inconsistent, this was because of rhizosphere of the walnut secretion types andquantity, and microorganism that displayed the different functions to each kind of soilenzyme's synthesis. The microorganism numbers in the rhizosphere soil varied significantlywith ages of walnut trees. Compared with the bulk soil, the bacterium and fungi quantity inrhizosphere soil increased along with the age increasing, actinomycetes quantity reducedalong with the age increasing and bacterium, fungi, and actinomycetes quantity reduced withthe depth of spatial profile. |
