Study On The Allelopathic Pathways And Mechanisms Of Solidago Canadensis L.

Canadian goldenrod (Solidago canadensis L.) is an invasive plant native to North America. This species was introduced into China as an ornamental plant in 1930s and became a serious weed after the 1980s. S. canadensis is an allelopathic weed in many crops and weeds. We studied 4-pathways of allelochemicals release:volatiles, leachates from stems and leaves, root exudation and decomposition of its residue. S. canadensis was used as donor and wheat (Triticum aestivum) and radish (Raphanus sativus) as recipient plants. And the main allelopathic pathways of S. canadensis were clarified. Then the compound n-hexadecanoic acid was isolated from S. canadensis extracts by organic solvent. The compound inhibited the seedling growth of wheat significantly. Subsequently, to clarify allelopathic potential and its preliminary mechanism of S. canadensis on wheat, study on a-amylase activity, lipid peroxidation and root activity of wheat treated by S. canadensis extract solution was carried out. The results were as follows:In this article, Petri dishes with filter paper and sand culture methods were used to study volatiles, leachates from stems and leaves and decomposed residue. The S. canadensis seedlings were grown with 1/4 Hoagland nutrients solution to examine the root exudation. The results suggested that volatiles and root exudates from S. canadensis had no remarkable effects on recipient plants. However, leachates from stems and leaves and decomposed residue of S. canadensis were allelopathic to seed germination and seedling growth of wheat and radish, and the allelopathic effects increased with increasing concentrations. At the highest concentration 0.1 g/mL, the inhibition of germination, root length and shoot length in wheat by S. canadensis leachates was 15.6.67.2 and 34.0%, respectively; while for radish was 27.6、62.3 and 39.5%, respectively. For S. canadensis decomposition, at the highest concentration 0.05 g/mL, the inhibition of germination, root length and shoot length in wheat was 21.2、82.0 and 67.7%, respectively; while for radish was 75.0、70.6 and 40.4%, respectively. So the main allelopathic pathways of S. canadensis were leaching and decomposition of its residue.The 80% methanol extract from S. canadensis was isolated and identified by silica gel column chromatography, Sephadex LH-20 gel column chromatography, recrystallization, infrared absorption spectroscopy,1H、13C-nuclear magnetic resonance spectroscopy and gas chromatography-mass spectrometry. A compound, n-hexadecanoic acid, was isolated from the ethyl acetate extract. This compound inhibited the seedlings growth of wheat significantly, and the inhibition increased with its increasing concentrations. At 10μg/mL, inhibition has already reached significant level. At the highest concentration 1000μg/mL, the inhibition of root length and shoot length in wheat by n-hexadecanoic acid was 80.5 and 69.8%. n-hexadecanoic acid was one of allelochemicals from S. canadensis.Allelopathic effects of S. canadensis extract solution on seed germination and seedling growth were assessed in wheat. The results showed that extract solutions from the concentration of 0.025,0.05 and 0.1 g/mL of S. canadensis inhibited the seed germination and seedling growth of wheat significantly, and the inhibitory intensity increased with enhancing extract concentrations. Then study on a-amylase activity, lipid peroxidation and root activity of wheat treated by S. canadensis extract solution was carried out. These results suggested that the extracts not only inhibited a-amylase activity and increased root activity but also led to lipid peroxidation. This study supported the assumption that the changes of a-amylase activity, lipid peroxidation and root activity were associated with the inhibitory effects on wheat seed germination and seedling growth of S. canadensis extracts. It can be used as a baseline for the further study on allelopathic mechanism of S. canadensis.