作 者 ：李文良,张小平*,郝朝运,张慧
期 刊 ：生态学报 2008年 28卷 11期 页码：5445~5453
Keywords:Cercidiphyllum japonicum, seed germination, seed size, moisture content, temperature, light intensity,
摘 要 ：连香树（Cercidiphyllum japonicum Sieb. et Zucc.）属第三纪孑遗植物，被列为国家二级保护植物，种群的自然更新困难。在实验室条件下研究了连香树种子萌发的生物学特性，以了解该种自然种群更新困难的原因和机制，为其有效保护提供理论依据。经测定，连香树种子千粒重为(0.5821±0.0166)g，种子重量极轻且产量大。四唑染色法对种子生活力的测定表明有活力种子比率仅为19.8%±1.3%。种子吸胀时吸水量达种子干重的482.13%±8.54%。将种子划分为6种表面形态类型进行萌发实验，发现不同形态种子萌发率显著不同，大小适中的黄褐色饱满种子萌发率最高，可达91.25%±2.36%。仅用饱满种子进行萌发实验，验证主要环境因子对种子萌发过程的影响，结果表明，以滤纸置床时萌发率高且有利于种子萌发整齐；种子表面可能存在促进种子萌发的物质；种子萌发对于湿度的响应最为明显，适宜的萌发湿度是20%～25%；萌发具有广泛的温度和光照适应性，除5℃萌发率降低外，10～30℃之间的萌发率无显著差异，随温度升高，萌发开始时间提前，萌发速率加快，幼苗活力指数增加；过弱光照不利于幼苗生长。种子萌发特性导致连香树种群自然更新困难的原因可能是：（1)虽然占有更多安全位，但小种子在竞争中处劣势；（2)生境片断化减少了种子产量也降低了种子质量；（3)较低温度条件下启动萌发有利于幼苗的物质积累，但增大了种群的风险；（4)林下光照不足使幼苗根茎生长严重失衡；(5)湿度依赖易造成爆发型萌发。
Abstract:Cercidiphyllum japonicum Sieb. et Zucc., one of the tertiary relict plant species, is the only species in a single genus, Cercidiphyllum, of the family Cercidiphyllaceae which is native to China and Japan. It was listed as one of national protected plants at the second category in China because of its extremely low ability of regeneration in natural population. In present research, the biological characteristics of seed germination were surveyed experimentally for the species, so that what conditions seed germination requires in natural regeneration would be clarified. C. japonicum during the period of fructification releases many compressed, winged seeds which are quite light with the 1000-seed weighting 0.5821±00166g. The percentage of viable seeds was tested by TTC(1.0%) to be 19.8%±1.3%, nearly close to germination percentage(GP). The imbibitional rate of seeds was 482.13%±8.54% in 14 hours. All seeds could be classified into six kinds of forms according to their surface morphology, each form having its own unique GP of seeds which differs significantly from each other, with the plump seeds of snuff color and moderate size being the highest of 91.25%±2.36%. The effect of several important environment factors on seed germination was tested for the plump seeds. The results showed that germination may be facilitated by some substance on seed capsule and the filter paper was approved to be an appropriate germination texture in comparison with sand. The germination was also affected by moisture content(MC) remarkably and the optimal range was 20%-25%. The germination could occur in an abroad range of light intensity and temperature. With exception of the decrease of GP at 5℃, temperature had no significant effect on GP, and the germination rate did, however, increase gradually with raise of temperature. Seedlings hadn′t adapted well to extremely low light intensity. To sum the above results up, the immediate causes that made it difficult for the natural populations of C. japonicum to regenerate may be inferred as follows: (1) small seeds could impose restriction for its success in competition with other plant species; (2)Quantity and quality of seeds were both decreased by erosion of habitat fragmentation; (3) seed germination in low temperature conditions led population to be exposed to danger, although favorable to accumulation of metabolic substances; (4) growth of root and stem was negatively influenced by extremely low light intensity under forestry; (5) Rapid germination could be possibly initiated by positive correlation with MC.
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