Allelopathic activity and metabolite differences of walnut leaf litter in the three main producing areas of Shaanxi Province

【Objective】To explore the effects of latitude factor on the allelopathic activity and metabolites of walnut leaf litter， so as to provide a theoretical basis for the deep development and utilization of walnut leaf litter and composite planting under walnut forest.【Method】Taking the leaf litter of walnut from Huanglong， Linwei and Shangzhou， the three main production areas of Shaanxi Province， as research objects， the allelopathic effects of aqueous extract and 70% ethanolic extract on wheat were studied by indoor bioassay. The optimal extraction solvent was selected，and the appropriate solvent extracts components were identified by liquid chromatography-tandem mass spectrometry LC-MS/MS to further explore the allelopathy of the best solvent extracts on wheat and ryegrass and screen the sensitive receptors.【Result】Under the same experimental conditions， the yield of walnut leaf litter extract varied in different producing areas， and the colors of two extracts deepened with decreasing latitude. The allelopathic activity of the same concentration treatment solution was ethanolic extract＞aqueous extract， indicating that ethanol could be used as a suitable solvent for extracting allelopathic substances from walnut leaf litter. The sensitivity level to the allelopathic effect of ethanolic extract was ryegrass＞wheat， indicating that ryegrass could be used as a sensitive receptor for subsequent experiments. The allelopathic activity of walnut leaf litter in different producing areas was in the order of Huanglong＞Linwei＞Shangzhou. A total of 1139 metabolites in 13 categories were detected in the 70% ethanolic extract of walnut leaf litter from the three regions. A total of 601， 716 and 664 metabolites were detected in Huanglong， Linwei and Shangzhou respectively， all of which were mainly lipids and lipidlike compounds. There were 7 types and 27 species of metabolites with a relative content greater than 1% in leaf litter， mainly organic acids. Five of these metabolites， including succinic acid,4-hydroxybenzoic acid， malic acid， quinic acid and caryophyllene oxide， were known allelopathic substances.【Conclusion】The synthetic allelopathic effects of walnut leaf litter extracts from the different producing areas decrease with the decrease of sampling latitude， which may be due to changes in the walnut growth environment causing different types and contents of allelopathic substances in the leaves， thereby affecting the allelopathic activity of the extracts.