中国三种水韭属植物的地理分布与生境特征

The geographic distribution and habitat of the Isoetes plants in China

水韭属 (Isoetes)是水韭科中的孑遗属 ,分类上属拟蕨类 ,对研究蕨类植物的系统演化具有重要价值。由于人类活动对其水生生境的破坏 ,水韭属植物在我国的分布范围及其种群数量日趋减少 ,濒临灭绝 ,其中 ,高寒水韭(I.hypsophila)、云贵水韭 (I.yunguiensis)和中华水韭 (I.sinensis)已被列为国家一级重点保护野生植物。对原产中国的 3种水韭的地理分布与生境特征进行调查 ,将为合理保护该属植物提供相关基础数据和科学依据。本文野外实地考察了原产中国的 3种水韭属植物的现存种群及历史记载曾经分布但现已绝迹的水韭属植物种群 (绝迹种群 )所在地。在每一调查点 ,测定了各样点的海拔高度、水体基底状况以及水体pH值等生境特征 ;在现存种群所在地 ,分别记载了所见水生植物种类、水韭种群规模及其生长状况 ,并采集和鉴定了 3种水韭属植物及其伴生种。调查发现 3种水韭属植物种与种之间为间断分布 ,且具有垂直梯度差异 ;种内各种群之间相互隔离 ,各种群的个体数均偏少 ;现存种群所生长的水体及其水体基底的pH特性无明显差异 ,为酸性或中性 ;绝迹种群所在的原生境已遭到严重破坏 ,一些地点的水体pH和基底pH与以往存在水韭的时期相比已明显升高。此外 。

Isoetes is a genus of primitive vascular plants classified in the subdivision Lycopsida and occupies a very important position in the evolutionary history of the pteridophytes. In recent years, Isoetes has declined rapidly in population quantity (number) and has even disappeared from many locations in China's Mainland. The genus is now considered to be rare and threatened or endangered in China and is listed among first category protected plants. The progressive decline in populations of Isoetes in China's Mainland has been attributed to on-going anthropogenic changes; however, no data have been adduced to support this assumption. In this study, all present locations of Isoetes populations and locations where the genus had been previously recorded but is now extinct were investigated in China's Mainland. The habitat characteristics, including elevation, water pH value and the conditions of substrate were measured at each site. Associated plants growing together with Isoetes were collected from each population. The result indicated that the geographic distribution of Isoetes in China's Mainland is discontinuous and that every population of Isoetes is insulated from other populations. The three species of Isoetes in China's Mainland occur at different elevations. The current populations showed no obvious differences in water pH and other characteristics. But habitats where Isoetes plants had been extirpated currently have higher water and substrate pH values compared to the period when the sites supported Isoetes populations. These sites also had higher readings than the current locations of remaining Isoetes populations. This study indicates that populations of Isoetes growing in marshy areas close to farmland are faced with intense competition from other hydrophyte species whose proliferation is encouraged by the use of fertilizers in adjacent farmland. The populations of Isoetes growing in the freshwater intertidal zone avoid competition with other hydrophytes because of the periodic fluctuation of water level and thus grow comparatively well. The results indicate that the geographic distribution and occurrence of Isoetes plants in China's Mainland is closely correlated with elevation, water pH, competition with other species, and water depth.