The Invasion Mechanism And Control Measures Of Cenchrus Pauciflorus In Meadow Grassland

The project of grassland desertification control was conducted in the northwest of Liaoning Province in 2009-2015. Zhangwu County was one of the controlling areas. Because of the long-term lack of control of grassland weeds, Cenchrus pauciflorus spread all over the county rapidly, and trending for all grassland of our province, leading to severe impacts to the grassland ecological environment and herdsmen yielding and travel. In this paper, Cenchrus pauciflorus in meadow grassland as the object, its occurrence and distribution laws, germination and dormancy characteristics, the invasive mechanism such as photosynthetic physiological characteristics, allelopathy, competitive effects on other native species and the influences of plant communities, and control measures, chemistry, biology, and physicas were investigated and studied.Cenchrus pauciflorus mainly distributes in 4 counties in grassland of Liaoning province, Zhangwu,Fumeng, Yixian, and Lingyuan county, which were the areas of the Liaoning northwest grassland desertification control project. Cenchrus pauciflorus began emergence in late April, June 11 to 25 reached the peak and stopped in early August; The tiller peak were early July, fruit maturing began in early August, late September reached the peak; stopped growing in October 10.The appropriate temperature for the gemination of Cenchrus pauciflorus seeds were 20-25 ℃. pH value had no obvious influence on seed germination. In the suitable moisture conditions,the germination rates of the small naked seed and the big seed in one thorn were the same, but the big seed germinated earlyer than the small.The seeds of Cenchrus pauciflorus could germinate and unearth normally in 3-10cm buried depth, and the more shallow buried, the more quickly unearthed. Cenchrus pauciflorus seeds had dormancy, and they could spend the dormancy period when store for 75d at room temperature, and low temperature was not the essential condition for germination.The light saturation point(LSP) of Cenchrus paucifloruswas 1573.74μmol·m-2·s-1, the light compensation point(LCP) was 75.16μmol·m-2s-1, and the maximum net photosynthetic rate(Pnmax) was 20.39μmol·m-2s-1, which was heliophile plant. Cenchrus pauciflorus had wider effective optical radiation range and the higher maximum light photosynthetic rate than its two associates plants Digitaria Sanguinalis and Chenopodium album.Cenchrus pauciflorus had allelopathy. By soaking with the water extracting solution from leaves of Cenchrus pauciflorus, the germination speed of Medicago saliva and Bromus inermis seeds were delayed, and the higher the solution the slower the germination. The germination rate of Bromus inermis seeds were reduced, but the Digitaria sanguinalis seeds improved. Roots and rhizosphere soil water extract on the germination rate of 3 plants seeds, Medicago saliva, Bromus inermis and Digitaria sanguinalis had no significant effect; the seedling radicle growth of Medicago saliva and Bromus inermis were obviously inhibited, of Digitaria sanguinalis inhibited by high concentration and promoted by the low.Tests for sowing Cenchrus pauciflorus seedings in mixture of Medicago saliva, Digitaria sanguinalis or Bromus inermis showed that their growth have been seriously inhibited and the relative yield decreased significantly when they sowing mixed with Digitaria sanguinalis. The height of Cenchrus pauciflorus were inhibited greatly and the dry mass accumulation decreased by hybriding Digitaria sanguinalis. But Digitaria sanguinalis had relative response, whose growth were promoted.The diversity of terrestrial plant in invaded area decreased with Cenchrus pauciflorus invading, the diversity index(H), dominance index(D) and evenness index(E) were all in the order no hazard areas (damage degree<15%)> mildly invaded areas (damage degree 16%-35%)> moderately invaded areas (damage degree 36%-50%)> heavily invaded areas (damage degree> 50%). Which were that,the higher the invaded degree, the lower the plant diversity, the more concentrated the plant species, the lower the species evenness and the simpler the structure of plant community. The powerful invasiveness of Cenchrus pauciflorus were leading to decreases to the dominance of the artemisia plant of asteraceae family and the chenopodium plant of chenopodiaceae family in the plant community.The results showed that the mechanical tillage could significantly reduce the emergence rate of Cenchrus pauciflorus by large area demonstration measuring, the germination rate could be reduced by 64.16% in the next year; Continuous cutting ears for 3 years, the germination rate could be reduced by 85.21%. Several herbicides screening tests showed that the two herbicides, quizalofop-p-ethyl and nicosulfuron. were the best to control Cenchrus pauciflorus in grassland. The quizalofop-p-ethyl and nicosulfuron of 40% lower volume appending adjuvane were detected, suggesting that the controlling effects had no differences between 40% lower volume with adjuvance and 100% volume alone. Spraying the leaves herbicides, quizalofop-p-ethyl, nicosulfuron and clethodim in mixture of soil herbicides, acetochlor and imazethapyr, could control Cenchrus pauciflorus effectively, and also could reduce the application frequency, save manpower. The investigation showed that sowing Medicago sativa, Astragalus adsurgens, Coronilla varia, Agropyron desertorum, Lolium perenne, Leymus chinensis and Elymus dahuricus had inhibitted the growth of Cenchrus pauciflorus significantly. The height, tillers, number of thorn bud and caryopsis in sowing areas were all fewer than the blank area, whose controlling effects were significant.