疏勒河上游地区植被物种多样性和生物量及其与环境因子的关系

物种多样性与生物量及其环境因子的关系是生态学和环境科学领域的热点问题,而多年冻土退化的生态效应是冰冻圈科学研究的重要内容之一。因此,本研究以疏勒河上游地区21处试验样地的9种类型植被为对象,初步分析物种多样性和群落盖度、生物量及其同海拔梯度、土壤理化性质和多年冻土区活动层厚度的关系。结果表明,物种多样性与群落盖度、生物量存在显著的“单驼峰型”关系,同海拔梯度关系满足“中度膨胀”理论。另外,0～40 cm深度土壤中有机质和全氮含量高,速效养分含量适中,而pH值、全钾和全磷低,则使植被群落盖度升高、生物量增加,物种多样性表现出先增加后减少的趋势,而具有高饲用价值的莎草科类植物增多,杂草类植物减少。定量分析表明,多年冻土退化,活动层厚度增加,土壤pH值升高,有机质、全氮、速效磷和速效氮含量明显降低,全钾和速效钾含量增加至一定程度后减少;从而导致植物组成由湿生型逐渐向中旱生乃至旱生型转变,植被类型由高寒沼泽草甸演替为高寒草甸、黑土滩及高寒草原,最终成为沙化草地,群落盖度不断降低、生物量不断减少;功能群类型中高饲用价值的莎草科类植物不断减少,而禾本科、豆科及杂草类植物先增加后减少,致使物种多样性同样表现出先增加后减少的变化趋势。

Species diversity of vegetation in relation to biomass and environmental factors in the upper area of the Shule River

The relationship of species diversity with biomass and environmental factors is a hot topic in ecological and environmental sciences. Cryospheric science includes important research concerning the ecological effects of permafrost degeneration. This study provided an analysis of changes in species diversity, community coverage and biomass in relation to elevation gradient, soil physicochemical properties, and depth of permafrost active layer for 21 plots of nine vegetation types in the upper Shule River area of the northeastern Qinghai-Tibet Plateau. There were “Single-hump Type” relationships between species diversity and community coverage as well as biomass, confirming the “Moderate Inflation” theory between species diversity and elevation gradient. In the 0 to 40 cm layers of soils containing high contents of organic matter and total nitrogen, medium levels of available nutrients and with decreases in pH, total potassium and total phosphorus, the community coverage and biomass increased while species diversity initially increased but then decreased. At that time, sedge plants of high feeding value increased, while weed plants decreased. Quantitative analysis revealed that as permafrost degraded, the thickness of the active layer and soil pH both increased, while the contents of organic matter, total nitrogen, available phosphorus and available nitrogen all significantly decreased while total potassium and available potassium increased to a lesser extent but then reduced in the active layer (0-40 cm). As a result there was a gradual change in vegetation composition from wetland plants to mesoxerophytes, and later, to xerophytes. Sequentially, the successive stages changed from alpine marsh meadow to alpine meadow, to “black-soil-beach” grassland and alpine steppe, and eventually to desertified grassland. Along with this process, community coverage and biomass decreased, and sedge plants of high feeding value diminished as a functional group. However, grass, legumes and weeds in plant communities initially increased but then decreased, and species diversity showed the same trend.