Title: Influence of environmental factors on seed germination of<i>Bombax malabaricum</i>DC.
Abstract: 木棉(<em>Bombax malabaricum</em> DC.)是一种可以生长在干热河谷的落叶大乔木。河谷内,木棉成年树木生长良好,有大量结实,而其周围却很少有种苗出现。通过室内条件研究木棉种子的物理特性和萌发的生物学特性,可以了解该物种种子萌发对环境因子的需求,为探讨木棉在干热河谷内自然种群更新难和萌发阶段对这一特殊生境的适应性提供理论依据。经测定,木棉种子千粒重为39.08 g,比同科的其它物种要轻。四唑(TTC,1.0%)染色测定种子生活力的结果表明有生活力种子占64.0%。种皮对吸胀无障碍,种子在25 ℃吸胀2 d时就开始萌发。检测了环境因子对种子萌发和幼苗生长的影响,结果表明,种子萌发对光照不敏感而且对温度有较广的适应性,15-35 ℃都可以萌发,25-35 ℃萌发率无显著差异,但随温度升高,萌发速率加快,幼苗长势增加;萌发过程对渗透胁迫敏感,聚乙二醇(PEG)浓度为0.10 g/mL时萌发率较对照显著下降,0.15 g/mL时种子就不能萌发;室温吸胀24 h的种子对热激敏感,42 ℃热激2 h后萌发率就已经显著下降;室温下水杨酸(SA,1, 10, 100 mg/L)浸种24 h,没有提高种子在萌发期间对干旱和热激的抗性。可见,高温和干旱是限制木棉种子成功萌发的关键因子,然而发现,温度较高时水分过大也会造成萌发后幼苗的死亡。;<em> Bombax malabaricum</em> DC. is a deciduous tree that can grow in the dry-hot valley biome of southwestern China. In the dry-hot valley, the adult trees of <em>B. malabaricum</em> produce many seeds, however, few seedlings are found around the mature trees. This discrepancy has important consequences for conservation and reforestation efforts. Therefore, we measured the physical and biological characteristics of seed germination to determine the required environmental factors for natural seed germination. The average weight of 1000 seeds was 39.08 g; the percentage of viable seeds tested via 2,3,5-triphenyl tetrazolium chloride (TTC, 1.0%) was 64.0%, similar to the percentage of germination under controlled conditions (25 to 35 ℃). The seeds of <em>B. malabaricum</em> had good water-absorption capacity; they began to germinate after soaking in distilled water for 2 days at 25 ℃. Seed germination was not sensitive to light and seeds germinated at a broad range of temperatures (15 to 35 ℃). Temperatures ranging from 25 ℃ to 35 ℃ had no significant effect on seed germination percentage. However, germination rate and seedling growth increased with temperature. Germination was sensitive to osmotic stress and decreased significantly in 0.10 g/mL Polyethylene glycol (PEG) solution, compared to the control in distilled water, and no germination occurred at 0.15 g/mL PEG. Seeds soaked in distilled water for 24 h at room temperature were sensitive to heat shock and germination percentage decreased significantly after heat shock for 2 h at 42 ℃. Pre-treatment by soaking with salicylic acid (SA, 1, 10, 100 mg/L) for 24 h with room temperature did not improve drought and heat tolerance of seeds during germination. In conclusion, drought and heat are two key factors that limit seed germination of<em> B. malabaricum</em>. However, an excess of water could also lead to seedling death after germination at relatively high temperatures.