Allelopathy Of The Dominant Noxious Weed Ligularia Virgaurea On Pasture Plants In Psychro-grasslands

Ligularia virgaurea is one kind of noxious compositae weed, distributed widely in psychro-grasslands in the east of Qinghai-Tibet Plateau of China. It is extremely harmful to psychro-grasslands by its monodominant species community. In this thesis, the allelopathy of L. virgaurea on 5 kinds of pasture plants was studied. The possible chemical relationship between the successful invasion of L. virgaurea and the actuality of psychro-grasslands degeneration was investigated, and its potential influence to the community structure of psychro-grasslands was deduced. We hope the results will provide valuable information for the selection about pasture plants kinds during vegetation recovery course of psychro-grasslands. The main results are as follows:1. Volatilization and eluviation were two ways which L. virgaurea released allelochemicals to surroundings. The results demonstrated that the volatile of growing L. virgaurea could inhibit the seed germination speed and germination rate of all tested pasture plants. The inhibitory effects on Elymus nutans and Bromus magnus were significant, while Poa annua and Festuca ovin were not very sensitive.2. The chemical constituents of L. virgaurea were analyzed by GC-MS. 18 major compounds were identified from the essential oil of L. virgaurea, accounted for 68.24% of the total. The main chemical components were 2-methyl-heptane (9.84%), 3-methyl-heptane (8.25%), Heptane (7.93%), 4-methyl-1-(methylethyl)-bicyclo [3,1, 0]hex-2-ene(7.79%), 3-methyl-hexane(6.38%), 2-methyl-hexane(5.54%) and D-limo-nene (4.70%) etc. Monoterpenoids accounted for 16.58% of the total.3. Both seed germination and seedling growth of all tested pasture plants were inhibited to different extent by aqueous extracts from L. virgaurea. The sensitivity of the 5 pasture plants species was orderly Poa annua > Bromus magnus > Festuca sinensis > Festuca ovina > Elymus nutans.4. Seed germinative stage of pasture plants was more obvious to be affected by the allelopathy of L. virgaurea than seedling growth stage. During seed germination, the germination index was more sensitive to allelochemicals than germination rate.5. The inhibitory effects of aqueous extracts from L. virgaurea roots was stronger than that from leaves, which might be related to the competition of the underground resources in natural grassland.6. Allelopathy might play an important role in enhancing the competitive ability and increasing the community of L. virgaurea, and was one of reasons of monodominant L. virgaurea community and grassland degeneration.7. According general change inclination of SOD,POD,CAT,MDA content and cell membrane permeability in leaves of Festuca sinensis,Bromus magnus,Elymus nutans and Poa annua which suffered from allelopathic stress, studied pasture plants can be divided two types, in which Festuca sinensis,Bromus magnus belonged to "slowness type" while Elymus nutans and Poa annua incline "sensitive type". There may be a critical point and a higher limen in each the former two species. Stress responses happened only when extent of stress reached the point. Each the latter two species have a relatively low limen. When the two plants were treated by aqueous extracts with low concentration, SOD, POD and CAT activities increased immediately to significant level.8. Praline content increased in all treatments and it is concentration-depended; the change of soluble sugar was inconsistent in the study.9. The protein components in Elymus nutans were changed by allelopathic stress, indicating that the protein synthesis had been adjusted by means of transcription and translation of gene so as to resist the harm of allelochemicals released by L.. virgaurea.10. Elymus nutans was the most sensitive pasture plant to the volatile of L. virgaurea in all 5 kinds of pasture plants while Poa annua and Festuca ovin had tolerance; The inhibitory effects of aqueous extracts from L. virgaurea on Poa annua was significant but Festuca ovin was not very sensitive. Accordingly, Festuca ovin could be used as preference during vegetation recovery course of psychro-grasslands.