| The allelopathic effect has become one of the important invasive mechanisms of alien invasive plants,and there are many ways to generate allelopathic compounds.Plant leaf litter releasing allelopathic substances in the environment is an important way during degradation in the soil.The Solidago canadensis L.is a typically noxious invasive alien plant in the world,and the allelopathic effect of leaf litter,especially allelopathy in the simulation of the actual ecological environment has not been reported.Therefore,we designed a pot experiment that leaf litter and green leaves were used as experimental materials and Lactuca sativa as receiver plant to verify the allelopathic effect of S.canadensis leaf litter and green leaves in the actual ecological environment.Secondly,through the pot experiment to study the effects of S.canadensis leaf litter and root exudates on soil properties and microbial community in the natural conditions.Finally,the physiological responses of Arabidopsis thaliana seedlings with difference concentration of metholic extract and two compounds from S.canadensis leaf litter were studied.The aim of this study was to identify the allelopathic effects and its chemical and ecological functions of S.canadensis leaf litter,and to elucidate the role between allelopathic effect and its invasion,to provide theoretical basis for the invasion mechanism.The results as follows:1.S.canadensis leaf litter and green leaves significantly inhibited the germination rate of L.sativa seed,and decreased plant height,aboveground biomass of L.sativa seedling,inhibition effects were increased with the increasing of concentrations and green leaves was higher than leaf litter.The peroxidase(POD)and catalase(CAT)activity increased at the concentration of 0.05 and 0.1 g/g,the CAT activity decreased when the concentration of green leaves increased to 0.2 g/g;S.canadensis leaf litter and green leaves causes an oxidative damage which resulted in the increasing of malondialdehyde(MDA)content in seedlings.We identified 27 and 34 kinds of compounds in the leaf litter and green leaves by GC-MS,and most of the terpenoids,ketones,phenols,alcohols,alkaloids.The content of total flavonoids and total phenols in soil and L.sativa seedlings also increased with the increasing of treatment concentrations.On the one hand,it proved that the allelopathy of S.canadensis leaf litter and green leaves inhibited the growth of L.sativa seedlings.On the other hand,the allelopathy of green leaves was stronger than that of leaf litter,it showed the timeliness of allelopathy of leaf litter in the actual environment,allelopathic effect of leaf litter may decrease with its decomposition.2.S.canadensis leaf litter and root exudates changed the soil physical and chemical properties,expecially the soil pH was changed from 6.55 to 7.34,and the amount of total nitrogen(TN)increased from 0.21 to 0.51 g/kg;leaf litter treatment significantly increased the abundance and diversity of bacterial communities,but there was no significant difference between low concentration and high concentration.S.canadensis root exudates had no significant effect on bacterial community diversity and abundance.Leaf litter and root exudates increased the total number and total relative content of soil compounds.The relative abundance of Sphingomonas,Acidobacteriales,Gemmatimonas decreased with the increase of leaf litter concentration and seedling density,however,the relative abundance of Methylobacillus,Rhizomicrobium,Novosphingobium and Bradyrhizobium increased with leaf litter treatments,and no significant effect with root exudates.Redundancy analysis(RDA)analysis showed that soil pH,TN and soil organic matter(SOM)content were not only positively correlated with the concentration of leaf litter and density of S.canadensis seedling,but also associated with bacterial communities.The results showed that the interaction between soil properties,chemical composition and soil bacterial community changed the soil ecological process,and the leaf litter and root exudates increased soil nutrient content and bacterial community diversity and relative abundance,which provides a rich soil ecological environment for the growth of S.canadensis.3.Crude extract and complund 1 from the S.canadensis leaf litter significantly inhibited the growth of A.thaliana seedling.The inhibition rate of root length was 66.82%,fresh weight and chlorophyll content were decreased by 58.46% and 41.79% at the concentration of 1 mg/m L of crude extract;high concentration treatment reduced the content of MDA increased antioxidant enzyme activities;the concentration of 0.5 and 1 mg/mL increased seedling soluble sugar and amino acid content,decreased the starch and soluble protein content.The concentration of the compounds 1 at 25,50 and 100 ?g/mL inhibited the growth of the A.thaliana seedlings,high concentration significantly increased the content of soluble sugar and reduced the content of starch and soluble protein,concentration at 100 ?g/m L the content of free amino acid was increased to 121.44 mg/g.There was no significant effect of compound 2 on the growth of seedlings and the changes in metabolites.These changes in physiological indicators of A.thaliana seedling demonstrated the allelopathic activity of compounds from S.canadensis leaf litter.The increase of soluble sugar and amino acid content and the decrease of starch and soluble protein content of the A.thaliana seedling showed that the strong allelopathic effect of leaf litter on the growth of A.thaliana seedling was achieved by changed the normal C and N metabolic pathways in plants,which provided the theoretical basis for the study of the allelopathic mechanism of S.canadensis leaf litter. |
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