孑遗植物水杉种子萌发的生理生态特性研究

Ecophysiological characteristics of seed germination of the relict plant Metasequoia glyptostroboides

从种子活力和抗氧化酶活性两个方面研究了温度和光照对孑遗植物水杉 (Metasequoiaglyptostroboides)种子萌发的生理生态特性的影响。实验结果表明 ,萌发温度对水杉种子的活力和抗氧化酶活性有较大影响 ,在 19-2 8℃范围内 ,种子的发芽率、发芽速率、活力指数、脱氢酶及超氧化物歧化酶 (SOD)、过氧化物酶 (POD)和过氧化氢酶 (CAT)等抗氧化酶活性均较高 ,其中在 2 4℃条件下最高 ;当温度低于 15℃或者高于 32℃时 ,种子活力很低 ;10℃条件下种子几乎不萌发。可以认为 ,水杉种子萌发的适宜温度范围为 19- 2 8℃ ,最适温度为 2 4℃。光照萌发试验表明 ,6 5 μmol·m-2 ·s-1(12h/d)光照对水杉种子的萌发有较大的抑制作用 ,黑暗条件更适于水杉种子的萌发。自然状态下水杉种子质量很差 ,空瘪率超过 90 % ,加之产地春季温度不适于水杉种子的萌发 ,这两者可能是限制水杉种群更新的重要因素。这也许是水杉种群中缺乏幼苗和幼树的原因之一。

Metasequoia glyptostroboides, known as a “living fossil” that was once widely distributed in the Northern Hemisphere, is now only found in a few restricted places in China. Many researches have been done on this species, but few on its seeds. Seed, as a key phase of spermatophyte life cycle, is important for regeneration and dispersal. Seed germination, which can be considered the initiation of the spermatophyte life cycle, is easily affected by environment. We studied the effects of temperature and light on ecophysiological characteristics of seed germination of M. glyptostroboides. Seed samples were collected from Lichuan City, Hubei Province, and stored at -20℃ before the experiment. A temperature gradient from 10℃ to 35℃ was used to study the effect of temperature on seed germination. Germination percentage, vigor index, and activities of dehydrogenase and antioxidant enzymes were used as a measure of seed vigor and stress resistance. The results indicated that temperature had a strong effect on seed vigor and activities of antioxidant enzymes. The germination rate, vigor index, and activities of dehydrogenase and antioxidant enzymes of M. glyptostroboides seeds were higher when temperature ranged from 19℃ to 28℃, whereas seed vigor declined greatly when the temperature was above 32℃ or below 19℃, and little germination was observed below 10℃. Our results imply that a temperature ranging from 19℃ to 28℃ is suitable for seed germination, with an optimum of 24℃. Seed germination was greatly inhibited by light (65 μmol·m -2 ·s -1 , 12 h/d), which implied that the germination of M. glyptostroboides seeds requires dark conditions. The seeds were of poor quality with the percentage of empty seed over 90%. The unsuitable temperature in the original habitat of M. glyptostroboides, together with the poor seed quality might be important factors limiting the regeneration of the species, and this might explain the lack of seedlings and saplings in M. glyptostroboides populations.