The Communtiies Characteristics, Biodiversity And Stability Of Artificia Alfalfa Grassland Plant In Loess Reigion

The changes of the communities characteristics,biodiversity and stability of alfalfa grasslands communities under different fertilizations,different growth age alfalfa grasslands communities in cropping wheat-alfalfa rotation system from the trial of long-term located fertilize.and the investigation of different growth age alfalfa grassland in gully region of the Loess Plateau were analyzed,respectively,to provide the scientific basis for sustainable and efficient use of artificial alfalfa grassland in Loess Region.The results were as follows:1.The species diversity indexes and ecological dominance index of the continuous cropping alfalfa grassland under different fertilizer treatments did not significantly differ,but the vegetation biomass tended to obviously increase,and the yield and importance value of alfalfa populations also raised significantly.Pmanure could maintain species diversity and stability of communities to some extent,and enhance alfalfa grassland productivity.2.After fertilizer treatments,niche breadth of alfalfa population increased and the competitiveness relatively strengthened;niche overlaps and competitives between two forbs were the larger and more intense,while the competitives.between Medicago sativa and other species were relative ease.fertilization can enhance the competitive of alfalfa populations, reduced the pressure between two species and improve the stability of communities.Under different fertilizations,the relationship between species diversity and productivity in the continuous cropping alfalfa grassland had been some changes, generally showed a negative quadratic function.3.The vegetation biomass,species diversity and ecological dominance index of the alfalfa rotation grassland,and the important value and yeild of alfalfa populations with the growth years decreased at first and increased subsquently decreased,but the species richness index and the aboveground biomass of forbs were opposite trends.After artificial grassland 3 years old,the stability of community productivity began to decline significantly,artificial glassland was in significantly degraded situation with the growth years of alfalfa and forbs prolonged invasion.4.The relationship between species diversity and productivity in alfalfa rotation grassland had undergone some changes with the plant years extension,which is closely related to interspecific competition.In rotation glassland the ecological amplitude (0.60)of alfalfa populations was the most wide,and the ecological amplitude of forbs such as Peduncularis(0.58) were larger , alfalfa and Peduncularis attached to the overlap value(0.995).maximum,and with other forbs also higher degree of overlap,the competitions between Medicago sativa and fors were most intense,which led to the sowing grassland degrade.5.The stability of alfalfa grassland in rotation was best in 3 years old,and later reduced with the decline in grassland productivity and biological diversity,grassland artificial would soon degrade,fertilization may be appropriate to delay the process of natural succession of artificial glassland.6.Artificial alfalfa grassland communities began to evolved toward the original vegetation community after about 26 years,was gradually replaced by bungeana community,which marked the alfalfa pasture has been completely degraded.After age 6 of grassland succession,the species diversity increased significantly,the structure of communities tended to be more complex,and its ecological stability relatively increased,showing that the artificial alfalfa grassland was in a stage of regressive succession.7.The relationship between species diversity and productivity had undergone some changes in alfalfa artificial grassland with the succession process forward,the overall relationship between them was a negative quadratic function under different under different successional time and habitat conditions.Maximum overlap occured between alfalfa and Peduncularis,its value was 0.99,there were the most competitive among alfalfa and forbs.The competitions between forbs and alfalfa for a limited resource is an important factor,which made the sowing grassland more degenerative.