|其他摘要||Xanthium italicum Moretti (family Asteraceae, Compositae) is an annual weed native to the Americas. It was first found and reported in 1991 in Beijing, and now has been widely distributed in China. X. italicum harmed the growth of crops such as corn, cotton, soybean, which caused great economic losses to the agricultural production in China. In this paper, the allelopathy of the volatilels of different parts of X. italicum soil microbial functional community structure, soil enzyme activity and soil nutrient content, which were important to further understand the allelopathy of X. italicum and increase agricultural production.
The essential oil was obtained from leaf, stem, fruit of X. italicum by steam distillation method, and their chemical composition was identified by GC-MS. In total 25, 23, and 27 compounds were identified from leaf, stemand fruit oils. Amaranthus retroflexus L., a dicot plant, and Poa pratensis L., a monocot plant, which can be found to grow in the habitats that were invaded by X. italicum, were used as tested species to evaluate the allelopathic effects of the plant’s volatile oils. Different amounts (20, 40, 80 g/1.4 L) of fresh cut leaves, stems and fruits of X. italicum were placed in air tight containers to simulate its natural conditions to emit volatile oils into the environment, and petri dish bioassay method was used to evaluate the phytotoxic activity of its essential oils at different concentrations (0.2 μl/ml, 0.5 μl/ml, 1 μl/ml, 3 μl/ml, 5 μl/ml). Our results showed that the volatile oils of different plant parts exhibited significant allelopathic effect both under simulated natural conditions and in the petri dish bioassay.
The effects of X. italicum invaded soil, sterilized invaded soil, invaded soil with
activated carbon on tested plants were also studied. Overall, root length, seedling height, fresh and dry weights of tested plant species were the highest grown in sterilized soil.
The effects of the aqueous extract of X. italicunm (0.025, 0.05, 0.1 g/ml) on the diversity of soil microorganisms, soil enzyme activities and soil nutrients were studied. Our results showed that total bacteria increased significantly when treated with aqueous extract and reached its maximum (38.5×106 CFU/g) when 0.05 g/ml extract was applied. Biolog analysis showed that the value of Average Well Color Development (AWCD) of treated soils was lower than the control. Principal component analysis (PCA) identified two factors in relation to carbon sources; and they explained 68.2% and 11.9% of the variation, respectively. The utilization of sugar, acid and amino acid by microbial community was highest. The aqueous extract significantly increased available N and available K of treated soils as well as the activities of soil urease and invertase. Correlation analysis revealed that soil urease activity and soil invertase activity and soil bacteria were positively correlated, but negatively correlated with actinomycetes. Our results suggested that X. italicum could possibly alter soil microbial community, soil enzyme activities and soil nutrient to create favorable growth conditions for itself.
We also compared the potential allelopathic effects of plant powder, aqueous and ethanol extracts of X. italicum on the diversity of soil microorganisms, activities of soil enzymes and soil nutrient. Our results showed that total bacteria increased significantly when soil treated with plant powder, ethanol extract and aqueous extract. Soil actinomycetes under three treatments were significantly lower than the control soil. Biolog analysis showed that the value of AWCD of treated soils was lower than the control. Principal component analysis (PCA) identified two factors in relation to carbon sources; and they explained 41.6% and 27.9% of the variation, respectively. The utilization of sugar, acid and amino acid by microbial community was highest. The soil enzyme activities and all soil nutrients under the treatments of plant powder and aqueous extract were higher than the control soil. Correlation analysis showed that bacteria number was positively correlated with soil enzyme activities (except protease and alkaline phosphatase), the number of fungi and the nutrient content.|