Effects of germination time on seed morph ratio in a seed-dimorphic species and possible ecological significance

Yang Fan, Jerry M. Baskin, Carol C. Baskin, Xuejun Yang, Dechang Cao, Zhenying Huang

萌发时间对种子异型性物种的种子比例的影响以及可能的生态意义

由于异型种子休眠和萌发的需求条件不同,异型种子物种能够在一年中不同时期萌发,这种萌发时间的差异可以影响生活史特性。我们研究了角果碱蓬二型种子的不同萌发时间对子代生活史的影响。在4月至9月的每月20日,将刚萌发的棕色和黑色种子移栽到近似野外生境当中。测量植株的物候和营养生长指标,以及子代种子数量、大小和萌发率。我们发现,晚萌发的种子比早萌发的种子形成的植株更小,产生更多更大的棕色种子(非休眠)。棕色种子幼苗建成时间比黑色种子短,而且由棕色种子萌发而来的植株比由黑色种子发育而来的植株在根茎比和繁殖分配方面更具有可塑性。晚萌发的棕色种子形成的植株大于晚萌发的黑色种子形成的。因此,种子二型种子比例随着萌发时间改变,能够帮助减轻晚萌发所带来的不利影响。角果碱蓬通过产生不同比例的二型种子来应对萌发时间的变异,这种灵活的策略有利于种群在不可预测的环境中维持和更新。

Background and Aims Diaspores of heteromorphic species may germinate at different times due to distinct dormancy-breaking and germination requirements, and this difference can influence life history traits. The primary aim of this study was to determine the effect of germination time of the two seed morphs of Suaeda corniculata subsp. mongolica on life history traits of the offspring.
Methods Germinated brown and black seeds were sown on the 20th of each month from April to September in a simulated but near-natural habitat of the species. Phenological and vegetative traits of the maternal plants, and number, size and germination percentage of the offspring were determined.
Key Results Germinated seeds sown late in the year produced smaller plants that had a higher proportion of non-dormant brown than dormant black seeds, and these brown seeds were larger than those produced by germinated seeds sown early in the year. The length of the seedling stage for brown seeds was shorter than that for black seeds, and the root/shoot ratio and reproductive allocation of plants from brown seeds were more variable than they were for plants from black seeds. Late-germinating brown seeds produced larger plants than late-germinating black seeds.
Conclusions Altering the proportion of the two seed types in response to germination timing can help alleviate the adverse effects of delayed germination. The flexible strategy of a species, such as S. corniculata, that produces different proportions of dimorphic seeds in response to variation in germination timing may favour the maintenance and regeneration of the population in its unpredictable environment.
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