关键词: 人工草地, 混播比例, 生产力, 超产效应, 土壤养分, 三江源

Abstract:

Establishing pastures by cultivation and sowing a mixture of perennial grass species is an effective measure to restore degraded grassland in the black soil zone of the Sanjiangyuan region. However， the changes in vegetation and soil nutrient characteristics under different mixed planting ratios are still unclear. Therefore， in the current study， Elymus nutans， Festuca sinensis and Poa pratensis cv. Qinghai were used to establish mixed swards at the rates of 1∶1∶1 （M₄）， 2∶1∶1 （M₅）， 1∶2∶1 （M₆）， 1∶1∶2 （M₇）， 2∶2∶1 （M₈）， 2∶1∶2 （M₉） and 1∶2∶2 （M₁₀） （the seed mixture ratios were calculated by weight of seed）. A monoculture of each component species was used as the control. The monoculture seeding rates of E. nutans， F. sinensis and P. pratensis cv. Qinghai were 30， 20 and 10 kg·ha^-1， respectively. We measured the differences in productivity， species diversity， the transgressive overyielding effect， net effect of biodiversity （composed of a complementarity effect and a selection effect） and soil nutrients in the different mixed planting ratios. The multi-criteria decision model TOPSIS was used for multivariate data evaluation to identify the best performing mixed planting ratio. It was found that aboveground biomass in the all seven mixed planting treatments were significantly higher than in the F. sinensis and P. pratensis cv. Qinghai monoculture treatments， but significantly lower than in the monoculture of E. nutans. The highest aboveground biomass among the mixed swards was found in the M₅， M₈， M₉ and M₁₀ treatments. However， there was no significant difference in underground biomass among the seven mixed species swards sown. In the mixed treatments， only M₅， M₈， M₉ and M₁₀ treatments had over yielding， which ranged from 40.4-71.1 g·m^–2. The net effect of biodiversity of M₄ and M₆ treatments were all less than 0， indicating that species competition in the community led to a decrease of community yield. However， the net effect of biodiversity of M₇-M₁₀ treatments were all greater than 0， indicating that the niche complementarity of species led to an increase of community yield. In the M₈ and M₉ treatments， the complementary and selection effects jointly contributed to the over yielding， while in M₅ and M₁₀ treatments， only the complementary effect was important and dominated the over yielding. The highest values of the content of organic matter， total nitrogen， total phosphorus， available phosphorus and available potassium in the topsoil were found in the M₆， M₇ and M₁₀ treatments. The multivariate data evaluation with the TOPSIS model showed that the M₁₀ treatment not only maintained high productivity and transgressive over yielding， but also significantly improved the soil nutrient status. This mixture is therefore recommended for the establishment of sown pasture in the Sanjiangyuan region.

Key words: artificial grassland, mixed planting ratio, productivity, transgressive overyielding effect, soil nutrients, Sanjiangyuan region