Study On Allelopathy Mechanism In The Invasion Of Alien Plant Solidago Canadensis L.

In recent decades, the frequency of exotic plants invasions has reached to an unprecedented level. Progresses had been made in allelopathy research of exotic plant invasion, but it is also possible to identify a range of researchable areas that still need attention, such as bioassay, the mechanism of allelopathy expression under environment stresses, rhizosphere biology of alien plant, identifying allelochemicals, searching for physiochemical response in exotic plant allelopathy, etc.In present work, the bioassay method was used to test the allelopahtic effect of Solidago canadensis L. on the target plants in laboratory condition, then the allelopathy of S.canadensis was further detected by allelopathy- competition-separation-based approach under different nitrogen regimes in near natural condition, and rhizosphere biology of S.canadensis was also analyzed through the investigation of soil microbial flora and the allelochemicals in 5. canadensis, which were extracted, separated and identified by GC-MS. Finally, physiobiochemical approach was employed to get first insight into the mechanism of allelopathy in S.canadensis. The results were summarized as follows:1 The extract of fresh and litter leaves of 5. canadensis both showed allelpathic potential, and fresh one was more stronger in the suppression on the the target plants of mungbean, lettuce, wheat, cabbage and pakchoi when compared with the same parts of its counterpart, Solidago decurrens Lour. In all target plant tested, wheat was the most sensitive receiver to extracts from the fresh and litter leaves of S. canadensis. Based on field trial using the method of radial area from the base of donor plant, S. canadensis also performed higher allelopathic potential in the suppression on wheat.2 The allelopathic potential of the rhizosphere soil was weaker when its distance from the surface of the root of S. canadensis was increased. It was indicated that S. canadensis had higher ability in the resource competition and exhibited its increasing allelopathic potential in the suppression of the target plant wheat as N supplies was decreased in the cocultured system, showing the allelopathic potential of 5. canadensis was 1.7 times as high as its resource competition especially in lower N supplies,.3 S. canadensis caused greater reduction on the number of fungi compared with control Solidago decurrens Lour. The reverse was true on bacteria and actinomycetes. Further analysis indicated that the root exudates from S. canadensis promoted the number of nitrite bacteria, aerobic azotobacter, sulphate reducer, ammonifier and aerobic cellulose-decomposer. But the growth of denitrifier, anaerobic cellulose-decomposer and desulphate reducer were inhibited by the invasive alien weed. The invasive plant, S. canadensis also increased the activities of soil enxyme as urease, dehydrogenase, cellulose etc.4 It was found that the allelochemicals most existed in the chloroform cream of 5. canadensis. The inhibition rate was 77.02% at chloroform cream of 1% concentration. Six groups of chloroform cream showed inhibition rate of 53.2%-64.3% at the 0.1% concentration. These groups contained the compounds as hydrocarbon, terpenoid, ester, hydroxybenzene and acid matter. The synergism and antagonistic relationship were evaluated among those allelopathic compounds.5 The allelopathy of S. canadensis significantly decreased the activities of protective enzymes such as SOD, POD and CAT in wheat, consequently increased the contents of free radical contents, decreased the uptake of nutrients from the enviroment and reduced the chlorophyll concentration, thereby, weakened the photosynthesis and inhibited the growth of wheat seedlings.