青藏高原腹地青藏苔草草原不同退化程度的植物群落特征

Plant community features of Carex moorcroftii steppe at different degradation degrees in the interior of Qinghai-Tibetan Plateau

为揭示高寒草地退化演替过程,采用野外调查方法研究了青藏高原腹地青藏苔草(Carex moorcroftii)草原不同退化程度的植物群落特征.结果显示:青藏苔草草原退化过程中优势种从未退化时的青藏苔草演变为轻度和中度退化程度时的青藏苔草和高山嵩草(Kobresia pygmaea)并存,重度退化程度时则无明显优势种;主要伴生种表现为湿生植物逐渐消失,中生和旱生毒杂草逐渐增加;植物物种丰富度指数和多样性指数均先增加后降低,中度退化程度最大,此时优质豆科(Leguminose)植物入侵,物种更替速率最大,β多样性指数最高.盖度、高度、地上总生物量均明显降低,而禾本科(Gramineae)生物量和豆科生物量均先增加后减少,中度退化程度时最大.相关分析表明,青藏苔草草原群落高度、盖度和均匀度指数与初级生产力呈显著正相关,相关系数分别为0.936(P<0.01)、0.961(P<0.01)和0.743(P<0.05).说明植物群落组分是青藏苔草草原不同退化程度植物群落结构和生产力变化的核心,在揭示青藏苔草草原逆向演替机制的过程中应注重阐明植物群落组分更替规律.

This paper aimed to determine the plant community characteristics of Carex moorcroftii steppe embedded in the zonal meadow at different degradation degrees. A field survey was undertaken during 2011 and 2012 to investigate the plant community characteristics at different degradation degrees of C. moorcroftii steppe in the interior of Qinghai-Tibetan Plateau. Sixteen 10 m × 10 m plots were designed at each degradation degree, each plot consisted of four subplots of 1 m × 1 m. In each subplot, all plant species present were identified and recorded for cover and height. The biomass was measured for four economic values of plants（Cyperaceae, Gramineae, Leguminose, Forbs） then harvested and dried. The α diversity of the plant communities was calculated by using the Shannon Wiener index（H）, the Pielou index（J）, richness index（S）, and the β diversity was estimated by Whittacker index（βws）. The relationships between height, coverage, species diversity, and the productivity of each economic value of plants and total productivity were analyzed at each degradation degree and degradation system. C. moorcroftii was found to be the dominant plant in the non-degraded C. moorcroftii steppe, replaced by the coexistence of Kobresia pygmaea and C. moorcroftii in the lightly and moderately degraded ones, with no obvious dominant plants identified in highly degraded steppe. With degradation of C. moorcroftii steppe, the hygrophytes decreased, and the mesophytes and xerophytes increased. The richness index and diversity index firstly increased and then decreased with the degradation of C. moorcroftii steppe, peaking at the moderately degraded degree, where legumes with good quality were indentified and the β-diversity index was the highest with the biggest replacement rate of species. Although the cover, height and aboveground biomass of plant community decreased, the aboveground biomass of Gramineae and Leguminose plants firstly increased and then decreased in the degradation process of C. moorcroftii steppe, peaking at the moderately degraded degree. Correlation analysis showed that the relationships between height, cover, evenness index and total productivity were significant positive at different degradation degrees of C. moorcroftii steppe in the interior of Qinghai-Tibetan Plateau. The plant community composition is an important indicator to be included in the process of revealing the mechanism of regressive succession of C. moorcroftii steppe.