Abstract:

This research investigated the community features， soil nutrient characteristics and their correlations in different degraded alpine meadows in Northern Tibet. Lightly degraded （LD）， moderately degraded （MD） and severely degraded （SD） alpine meadow sites were selected for study and our research used a combination of field investigation， laboratory measurement， variance analysis and redundancy analysis to elucidate the relationships between vegetation ecological characteristics and soil environmental factors for these three different alpine meadow degradation stages in Northern Tibet. It was found that： 1） There were 25 plant species from 20 genera and nine families present in the study area， and these were species with strong ecological adaptability， mainly from the in Cyperaceae， Poaceae， Asteraceae and Rosaceae families. Species associations commonly present across these alpine meadow sites included Kobresia pygmaea with Pedicularis longiflora， Leontopodium pusillum with K. pygmaea and Potentilla bifurca with Ajuga lupulina. Among these， K. pygmaea was the dominant species at LD and MD sites， although the functional groups were dominated by forbs. The perennial herb is the major vegetation component in Northern Tibet. 2） The characteristics of the studied plant communities， including aboveground biomass， height， density， frequency and vegetation cover showed a decreasing trend from LD to SD （P<0.05）. And the species Margalef index， Pielou index， Simpson index and Shannon-Wiener index of the LD sites had the highest values. 3） With increasing alpine meadow degradation， organic matter， total nitrogen， total phosphorus， total potassium， available nitrogen， available phosphorus and available potassium all decreased， while pH increased. 4） Species diversity index and the available phosphorus and total phosphorus across the series of degradation stages were significantly positively correlated. The aboveground biomass showed significantly positive correlations with total nitrogen. The factors contributing most strongly to vegetation growth in these alpine meadows at different stages of degradation were available nitrogen， organic matter and pH， respectively. This indicated a correlation between the degradation status of alpine meadows， plant community composition and soil nutrient status. In summary， the soil nutrient status， especially the role of soil nitrogen and phosphorus， must be considered when researching and managing alpine meadow degradation．

Key words: degraded alpine meadow, community features, soil nutrient characteristics, species diversity index, redundancy analysis