海拔梯度对藏北高寒草地生产力和物种多样性的影响

草地群落物种多样性和生产力在海拔梯度的变化规律及其关系,以及不同功能群的变化一直是热点问题,目前尚未得出一般性规律。本研究通过藏北地区那曲县日参波山样线的高寒草地样方调查实验,分析各海拔梯度(4485~4635m)植物群落生产力、结构和物种多样性的变化。结果表明,随着海拔升高,高寒草地植物群落生产力先增加后降低,并在海拔4535~4585m左右达到最佳;莎草类在群落由相对优势变为绝对优势,禾草类和杂草类的重要值以不同幅度下降,豆科类的重要值先上升后下降;物种丰富度、Shannon-Weiner多样性指数、Simpson多样性指数和E.Pielou均匀度指数均呈现"单峰"型格局,物种多样性指数与地上生物量呈正相关关系,但只能作为部分解释地上生物量变化的因素。

Effects of altitude on plant productivity and species diversity in alpine meadows of northern Tibet

Changes in the species diversity and productivity of grass communities along altitudinal gradients and the relationship between diversity and productivity are important issues in ecology,and can explain variations among functional groups.The aim of this study was to determine the variations in the species diversity and productivity,and the factors affecting them,in the alpine meadow ecosystem.Field surveys of alpine meadows were conducted at four different altitudes (around 4485,4535,4585,4635 m) in northern Tibet.Plant biomass and species composition were determined,and diversity indexes were calculated from the data.The productivity increased then decreased with rising altitude,and the highest productivity was around 4535-4585 m.In terms of functional groups,sedges moved from a comparative advantage to an absolute advantage as the altitude increased,while forbs and grasses became less important at different rates.Legumes became more important and then less important as the altitude increased.The species richness,Simpson index,Shannon-Wiener index,and Pielou evenness index were significantly higher at middle altitudes than at higher and lower altitudes (P＞0.05),leading to a hump-shaped curve in plots of species richness vs.altitude and diversity vs.altitude.There were positive correlations between biomass and the Shannon--Wiener index and between biomass and the Simpson index (P＜0.05),but not between biomass and the Pielou evenness index or biomass and the importance of functional groups (P＞0.05).These findings indicate that the productivity and diversity of alpine meadows in northern Tibet are strongly influenced by altitude,which is related to variations in many environmental factors.This information will be useful for developing strategies to manage and preserve this important ecosystem.