通过太湖野外调查、室内培养、种子与块茎萌发及幼苗生长试验,对太湖苦草(Vallisneria natans)种群的繁殖生态特征进行了研究。结果显示:1)苦草分配于有性繁殖部分的生物量较无性的大,分别占总生物量的25.0%±13.8%和10.1%±7.0%。雌花数与座果率平均分别为22.9±13.8朵·株^-1和73.3%±17.9%。雄株可以产生11~33个佛焰苞,每个佛焰苞内平均含有364±38朵雄花,每个雄花产生的花粉为128~184粒。每个果实内种子丰富,多达150~360粒,估算太湖苦草种群立地种子量可达1.68×10⁴~1.01×10⁶个·m^-2。但每年种群主要来自地下块茎和匍匐茎,水深、风浪等可能是种子苗难以在湖泊中定植成功的主要因素。2)苦草的块茎数量较大,平均90~226个·m^-2,是种群发展的强大物质基础。3)温度、光照、基质及种子保存方式与时间长短对种子发芽率均有较大影响。10 ℃时种子发芽率较低,仅8.35%±1.89%;20 ℃时发芽率较高,为56.73%±6.42%;30 ℃时发芽率有所降低,为43.55%±4.34%。种子发芽对光照有一定要求,20 ℃、无光条件下,种子发芽率下降63.6%。在没有湖泥为基质的情况下,发芽率下降36.5%。此外,随干燥保存时间增加,种子发芽率下降。4)块茎发芽对光照需求不大,但温度对块茎的发芽率有较大影响,10 ℃时发芽率为20.3%±5.7%,20 ℃时较高,达90.2%±12.6%,30 ℃时发芽率降低至60.4%±7.6%。5)光照对幼苗生长有一定影响。有光照的幼苗伸长生长比无光条件下慢,但生物量积累较大,有光的苗生长速度平均为0.56~0.70 cm·d^-1,无光的为0.86~0.96 cm·d^-1。试验结果还显示,苦草的块茎苗初期的伸长生长主要依赖于基部的根茎生长。6)根据研究结果认为,在湖泊中恢复苦草种群应主要利用地下块茎,种子只适用于相对静止的浅水池塘种植。

Vallisneria natans is a dominant submerged macrophyte in Lake Taihu. The biomass and quantity of propagules of V. natans were investigated in Lake Taihu in October, 2003 and in March, 2004. Seed and tuber germination, and development of seedlings produced from tubers under different conditions were also studied in the laboratory. Our objectives were to understand characteristics of the reproductive ecology in V. natans. The results showed that the biomass of asexual and sexual propagules was 10.1%±7.0% and 25.0%±13.8% of total biomass, respectively, and the biomass of sexual propagules was greater than asexual propagules. The average number of female flowers was 22.9±13.8 per individual plant, and seedset rate was 73.3%±17.9%. There were 11-33 spathes per individual male plant and 364±38 male flowers inside each spathe. Based on ourin situ investigation, we estimated a density of 6.29×10⁵-1.89×10⁶ microspores·m^-2 around V. natans populations in Lake Taihu. Seedlings produced from seeds were not able to survive in Lake Taihu, which is likely caused by factors such as wind, wave and water depth. Most populations in V. natans reproduced asexually from root tubers. We estimated a mean tuber density of 90-226 per square meter. Light, temperature, sediment, thermal fluctuation and seed age had a marked influence on germination rates. Germination rates of seeds stored for 4 months under water in the lake was 8.35%±1.89%, 56.73%±6.42% and 43.55%±4.34% at 10, 20 and 30 ℃, respectively. Seed germination rates stored for one year was 35.53%±3.53% under natural light conditions and decreased to 12.63%±2.86% under dark conditions. Germination rates of seeds stored for one or two years was 35.53%±3.53% and 12.63±2.86%, respectively. Germination rates of seeds stored for four years was near zero. Germination rates of seeds decreased under conditions without sediment. Tubers did not require light for germination. There was an optimal temperature of 20 ℃ for tuber germination to occur that was as high as 90.2%±12.6%. Biomass accumulation in seedlings produced from tubers under light conditions was greater than that in the dark, while leaves of seedlings grown in the dark were longer. Seedling increases in length mainly depends on the stems of the lower end of leaves. We present suggestions for restoration efforts of populations ofV. natans in Lake Taihu.