混播比例对三江源人工草地植被和土壤养分特征的影响

建植混播人工草地是修复三江源黑土滩退化草地的有效措施，但不同混播比例下植被和土壤养分特征的变化尚不明确。以垂穗披碱草、中华羊茅和青海草地早熟禾分别按1∶1∶1（M₄），2∶1∶1（M₅），1∶2∶1（M₆），1∶1∶2（M₇），2∶2∶1（M₈），2∶1∶2（M₉）和1∶2∶2（M₁₀）建植混播人工草地，并以各组分单播为对照，研究生产力、物种多样性、超产效应、多样性净效应（包括互补效应和选择效应）和土壤养分特征的变化，并采用多准则决策模型-TOPSIS进行综合评价，以筛选最佳混播比例，以期为三江源退化草地生态修复提供科学依据。结果表明：混播处理地上生物量显著高于中华羊茅和青海草地早熟禾单播的生物量，但显著低于垂穗披碱草单播处理，混播处理地上生物量在M₅、M₈、M₉和M₁₀处理较高。而地下生物量在混播处理间无显著差异。混播处理中，仅M₅、M₈、M₉和M₁₀处理存在超产，达40.4~71.1 g·m^-2。M₄和M₆处理的多样性净效应均小于0，说明由于物种竞争导致群落减产。而M₇~M₁₀混播处理的多样性净效应均大于0，说明物种生态位的互补使得群落高产。M₈和M₉处理中互补效应和选择效应共同主导了超产效应，而M₅和M₁₀处理中主要由互补作用主导超产效应。表层土壤的有机质、全氮、全磷、速效磷和速效钾含量在M₆、M₇和M₁₀混播处理中较高。TOPSIS模型综合评价表明，M₁₀混播处理不但可保持较高的生产力，还可显著提高土壤的养分含量，是三江源区人工草地建植的理想混播比例。

Effects of different mixed planting ratios on vegetation and soil characteristics of sown pasture in the Sanjiangyuan region

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.