天鹅洲湿地退化区土壤种子库与地面植被的关系初探

2015年1-7月在湖北石首天鹅洲麋鹿国家级自然保护区湿地退化区内选取30个样点，研究土壤种子库特征，并比较种子库与地表植被在物种组成上的差异。采用幼苗萌发法确定种子库物种组成和种子数量，通过样方法进行地面植被调查。结果显示，种子库萌发次序依次为禾本科（Gramineae）、苍耳（Xanthium sibiricum）和葎草（Humulus scandens）；在生长速率方面，葎草（0.4-1.2 cm/d）> 苍耳（0.2-1.0 cm/d）> 禾本科（0.1-0.4 cm/d）。退化区内种子库物种由18科、33属、34种组成，平均种子密度为6 153粒/m2，生活型以一年生草本植物为主（23种）；地面植被由21科、32属、32种组成，以多年生草本植物为主（21种）。种子库与地面植被兼有物种数为20种，物种相似性较高（Jaccard相似性系数和S?renson相似性系数分别为0.435和0.606），但地面植被的物种多样性和均匀度均高于种子库（Shannon-Wiener多样性指数2.488>1.886，Simpson多样性指数0.889>0.672，Pielou均匀度指数0.783>0.539）；种子库优势种为狗尾巴草(Setaria viridis)和早熟禾(Poa annua)，地面植被优势种为乌蔹莓(Cayratia japonica)、鸡矢藤(Paederia scandens)、接骨草(Sambucus javanica)。研究结果初步揭示了天鹅洲湿地退化区土壤种子库与地面植被的关系，可为退化湿地生态恢复提供理论指导和科学依据。

Relationship between Soil Seed Bank and Above-ground Vegetation in the Degraded Wetland Region of Shishou Swan Island Elk Nature Reserve, Hubei Province

The soil seed bank accumulates from seeds produced by above-ground vegetation and, to a certain extent, reflects the condition of past vegetation and can be used to predict vegetation composition and succession. Therefore, the study of soil seed bank composition and characteristics is important for evaluating seed reserves and the self-restoring potential of a degraded wetland ecosystem. In this study, the relationship and differences between seed bank and above-ground vegetation were investigated in the degraded wetland zone of Shishou Swan Island Elk Nature Reserve using a seedling germination experiment and field survey from January to July, 2015. The reserve is located on the north shore of lower Jingjiang River, part of a former channel of the Yangtze River. The nature reserve wetland area has been declining sharply since construction of Three Gorges Dam due to decreased water circulation, large scale expansion of Populus euramericana and other human activities. Soil samples for the seedling germination experiment were collected at 30 sites in January and stored in the laboratory. The seedling germination experiment was carried out from March 25 to July 25 and field investigation of vegetation at soil sampling sites was carried out July 22-23. Plant species and number, height and cover were recorded for the seed germination experiment and field investigation. In the germination experiment, Gramineae was the first to germinate, followed by Xanthium sibiricum and Humulus scandens. The growth rate of Humulus scandens (0.4-1.2 cm/d) was faster than Xanthium sibiricum (0.2-1.0 cm/d) and Gramineae (0.1-0.4 cm/d). The seed bank in the degraded wetland zone contained 18 families, 33 genera and 34 species with an average seed density of 6153 seeds/m2 and dominated by 23 annual herbs. The above-ground vegetation consisted of 21 families, 32 genera and 32 species, dominated by 21 perennials herbs. The soil seed bank and above-ground vegetation displayed a high similarity in species composition, sharing 20 species, a Jaccard similarity coefficient of 0.435 and a S?renson similarity coefficient of 0.606. However, species diversity and evenness were higher in the above-ground vegetation than in the seed bank; Shannon-Wiener diversity index 2.488 > 1.886, Simpson diversity index 0.889 > 0.672 and Pielou uniformity index 0.783 > 0.539. Dominant species in the seed bank were Setaria viridis and Poa annua, while dominant species in the above-ground vegetation were Cayratia japonica, Paederia scandens and Sambucus javanica. Our results revealed the relationship between the seed bank and above-ground vegetation in the degraded wetland zone of Swan Island and will provide theoretical and practical knowledge to support restoration of degraded wetlands.