Department of Biology, Middle Tennessee State University, Murfreesboro, TN 37132, USA.
Ann Bot. 2010 Dec;106(6):945-55. doi: 10.1093/aob/mcq189. Epub 2010 Sep 29.
Bulbils serve as a means of vegetative reproduction and of dispersal for many plants; this latter aspect making them analogous to seeds. However, germination of bulbils may differ considerably from seeds due to dissimilar anatomical structures and perhaps environmental cue perception. The few laboratory studies done on bulbils suggest that their germination is similar to that of seeds in the same habitats and to vegetative buds of winter-dormant plants. The present study is the first to examine how bulbil germination is controlled in nature in relation to dispersal (before vs. after winter of the same cohort) and to ambient temperatures.
Under laboratory conditions, temperature and light requirements for root and shoot emergences from bulbils of Dioscorea polystachya collected in September, 2005, February, 2006 (produced in 2005) and July, 2006 were determined. Effects of cold stratification and dry storage for releasing dormancy were tested on September and July bulbils. The phenology of dormancy release and of root and shoot emergences and the persistence of bulbils in soil were followed over time under field conditions.
Although a low percentage of bulbils collected in July or in September produced roots, but no shoots, in the laboratory and field, these roots died within approx. 1 month. Regardless of collection date, cold stratification markedly increased root and shoot emergences. Bulbils sown outdoors in October produced roots and shoots the following March and April, respectively. The soil bulbil bank is short lived.
Bulbils of D. polystachya are similar to seeds of many temperate plants being mostly dormant when dispersed in summer or autumn and overcoming dormancy with cold stratification during winter. Adaptively, bulbil germination primarily occurs in spring at the beginning of a favourable period for survivorship and growth.
球茎作为许多植物的营养繁殖和扩散的手段；后者使它们类似于种子。然而，由于解剖结构的不同，以及环境线索的感知，球茎的萌发可能与种子有很大的不同。对球茎进行的少数实验室研究表明，它们的萌发与同一栖息地的种子相似，与冬季休眠植物的营养芽相似。本研究首次研究了球茎在自然条件下是如何控制萌发的，包括与扩散（同一批次的冬季之前与之后）和环境温度的关系。
在实验室条件下，测定了 2005 年 9 月、2006 年 2 月（2005 年生产）和 2006 年 7 月采集的薯蓣多穗薯球茎的根和芽从球茎中出现所需的温度和光照条件。测试了低温层积和干藏对解除休眠的作用，分别对 9 月和 7 月的球茎进行了测试。在野外条件下，随着时间的推移，跟踪了休眠释放、根和芽出现的物候学以及球茎在土壤中的持久性。
尽管在实验室和野外，7 月或 9 月采集的球茎中只有一小部分产生了根，但没有产生芽，但这些根在大约 1 个月内死亡。无论采集日期如何，低温层积显著增加了根和芽的萌发。10 月室外播种的球茎分别于次年 3 月和 4 月生根发芽。土壤球茎库的寿命很短。
薯蓣多穗薯的球茎类似于许多温带植物的种子，在夏季或秋季传播时大部分处于休眠状态，在冬季通过低温层积来克服休眠。适应性地，球茎的萌发主要发生在春季，这是一个有利于生存和生长的时期。
