西藏高原高寒草原生态系统植被C/N值的分布特征及其影响因素

Distribution characteristics and its influence factors of vegetation C /N value of alpine steppe ecosystem in Tibetan Plateau

以西藏高原高寒草原生态系统的4个自然地带（高山草原、高山灌丛草甸、山地半荒漠与荒漠以及山地灌丛草原）的19个草地型植被为研究对象，采用野外调查与室内分析相结合的方法，对高寒草原生态系统植被C／N值的分布特征及其影响因素进行了研究。结果表明：西藏高原高寒草原植被C／N值总体上呈现出东西部低而中间高的态势以及斑块状交错分布的格局。不同自然地带间和不同草地型间植被地上部分和根系的C／N值有明显差异，且地上部分的C／N值均大于根系。19个草地型植被地上部分的平均C／N值为34．17，变异系数为35．87％；根系的平均C／N值为29．58，变异系数为40．02％。4个自然地带植被地上部分的平均C／N值为31．98，变异系数为13．82％；根系的平均C／N值为31．86，变异系数为16．92％。回归分析结果显示：植被地上部分C／N值与地上部生物量以及土壤全N和全K含量呈显著正相关、与植被高度呈显著负相关；根系C／N值与海拔和20～30em土壤容重呈显著正相关、与年均降水量和年均蒸发量呈显著负相关，这些因子均为影响西藏高原高寒草原植被C／N值的关键环境因子。总体上看，地理因子、气候因子和土壤物理因子对西藏高原高寒草原生态系统植被C／N值的影响不显著，而植被因子和土壤化学因子则对其有显著影响。

Taking vegetation of nineteen grassland types of four natural transects （alpine grassland, alpine shrub and meadow, mountain semidesert and desert, mountain shrub steppe） in alpine steppe ecosystem in Tibetan Plateau as research objects, distribution characteristics of vegetation C/N value and its influence factors in alpine steppe ecosystem were studied by means of combining field investigation and laboratory analysis. The results show that the vegetation C/N value of alpine steppe ecosystem in Tibetan Plateau appears generally a tendency with lower in east and west parts and higher in the middle part of Tibetan Plateau, and a patch distribution pattern. There are obvious differences in C/N value of above- ground part and root among different natural transects and different grassland types, and C/N value in above-ground part is higher than that in root. Average C/N value in above-ground part of vegetation of nineteen grassland types is 34.17 with coefficient of variation （CV） of 35.87% , and that in root is 29.58 with CV of 40.02%. While that in above-ground part of vegetation of four natural transects is 31.98 with CV of 13.82% , and that in root is 31.86 with a CV of 16.92%. Regression analysis result shows that C/N Value in above-ground part of vegetation has a significant positive correlation with above-ground part biomass, total N and total K contents in soil, and has a significant negative correlation with vegetation height; C/N value in root has a significant positive correlation with altitude and soil bulk density in 20-30 cm soil depth, and has a significant negative correlation with mean annual precipitation and mean annual evaporation. And these factors are the key environmental factors influencing vegetation C/N value of alpine steppe ecosystem in Tibetan Plateau. General, the influence of geographical, climatic and soil physical factors on vegetation C/N value of alpine steppe ecosystem in Tibetan Plateau is not significant, while that of vegetation and soil chemical factors is significant.