Philippi T
Am Nat. 1993 Sep;142(3):474-87. doi: 10.1086/285550.
Prolonged seed dormancy in desert annuals is thought to be an adaptation to environmental uncertainty. Germination spread over several years could reduce the year-to-year variation in the fitness of a genotype. Previous work has demonstrated that, for a number of species, not all viable seeds germinate under one set of conditions in the first year, but the subsequent fate of the dormant seeds has not been tested. In this study, germination experiments were performed on seeds of six species of winter annuals from Portal, Arizona. Seeds that do not germinate under good conditions in the first year germinate under the same conditions in subsequent years. However, germination fractions in the first 2 yr are not equal fractions of remaining viable seeds, which is the theoretical optimal behavior, and the germination distributions differ greatly among species. Germination under good conditions following a year of bad conditions for germination also differs among species. Germination behavior is age-dependent, and germination trials conducted on seeds of unknown ages from soil samples may give misleading results. These results indicate that seed dormancy acts as a form of bet hedging but that selection for an optimal distribution of germination across years may be weak.
沙漠一年生植物种子的长期休眠被认为是对环境不确定性的一种适应。多年间分散发芽可以减少一个基因型适合度的逐年变化。先前的研究表明，对于许多物种来说，并非所有有活力的种子在第一年的一组条件下都会发芽，但休眠种子随后的命运尚未得到检验。在本研究中，对来自亚利桑那州波特尔的六种冬季一年生植物的种子进行了发芽实验。第一年在良好条件下未发芽的种子在随后几年的相同条件下会发芽。然而，前两年的发芽率并非剩余有活力种子的等比例发芽率，而这是理论上的最优行为，并且不同物种间的发芽分布差异很大。在不利于发芽的一年之后，在良好条件下的发芽情况在不同物种间也存在差异。发芽行为依赖于种子年龄，对来自土壤样本的未知年龄种子进行的发芽试验可能会给出误导性结果。这些结果表明种子休眠起到了一种风险规避的作用，但跨年度发芽最优分布的选择可能很弱。
