| In recent decades, grassland on the Qinghai-Tibetan Plateau was degraded continuously, which have been paid high attention by human beings. And the restoration and reconstruction of degraded grassland have become an important issue. Building artificial grassland can not only solve the issue, but also meet the unbalanced question of forage provision. However, people found that the artificial grassland began degradation and renewedly became "black-soil-type" grassland after rebuilding three to five years, when artificial grassland was planted in the Yangtze and Yellow River Headwater Reign. This made that the work of improving degraded grassland was fallen into a passive position. In last three decades, the relationship between biodiversity and ecosystem function has emerged as a major scientific issue, with the unprecedented loss of biodiversity. Many experiments addressed that the increase of productivity, invasion resistance and stability in experimental grassland communities resulted from species richness of communities. However, some studies found that there was no relationship between productivity and biodiversity, and communities with more species were easily invaded by other species. Because there is no a definite conclusion in this respect, there are a lot of difficulties on theory directing practice. Therefore, In order to investigate productivity, invasion resistance and stability of artificial grassland, our experiment chose three kinds of perennial grasses-Elymus nutans, Festuca sinensis and Festuca ovina, which distributed widely in the east of the Qinghai-Tibetan alpine meadow, and was established in Hezuo branch of the Research Station of Alpine Meadow and Wetland Ecosystems of Lanzhou University(N34°55′, E102°53′, altitude 2900 m a.s.l., yearly average temperature and precipitation are 2.0℃and 557.8 mm), and last six years. In general,5-years of experiments indicated that:1. Species composition had a significant influence on forage community productivity, and there was a positive relationship between species richness and forage productivity. During the initial phase of communities. forage community productivity was increased when sown density increased. Fertilization significantly increased forage community productivity and the positive relationship between biodiversity and the productivity.2. Species composition had also a significant influence on forage community selection effects, and the positive relationship between species richness and selection effects became significant with increase of soil nutrient level. During the initial phase of communities, the value of selection became bigger with the increase of sown density. Fertilization had different influence on the selection seffect when communities were in different phase.3. The complementarity effects were influenced by species composition, and the values of complementarities were higher in the communities with high biodiversity than with low biodiversity. Increasing densities decreased the complementarity effects during the initial phase of communities. Fertilization significantly increased complementarity effects of forage communities.4. The increase of forage community productivity with biodiversity was resulted from joint effects of selection and complementarity, but with an increase of growth time, complementarity effects strengthened though time and substituted the role of the selection effect.5. Forage composition had also significant influence on the number of invading species, the number of individual invaders and their biomass. The ability of community to resist weed would significantly increased when forage biodiversity increased. During the initial phase of communities, high density communities had lower weed than low density communities. Fertilization significantly decreased the number of weed species and individual invaders, but increased weed absolute biomass.6. Community and population stability of forage were influenced by forage composition. Community stability had an increasing trend and population stabilities had different response, when forage biodiversity increased. The stability of community or population was not influenced by sown density. Fertilization had no influence on the community stability, but had different influence on the stabilities of different forage populations.7. In order to make artificial grassland to keep high productivity, invasion resistance and stability, forage composition should include Elymus nutans, Festuca sinensis and Festuca ovina, or Elymus nutans and Festuca ovina. Sown density should select 1600 plant·m-2 Perennial grasses should not be clipped, and forage communities should also be properly fertilized during growing seasons. So, the production of artificial grassland would reach 10 ton·hm-2.
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