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

Abstract

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.

Keywords: Germination timing; Suaeda corniculata; life history traits; maternal environmental effect; phenology; phenotypic plasticity; seed germination; seed heteromorphism.

Fig. 1.

Effects of germination date and seed type on length of key life history periods of Suaeda corniculata. (A) Vegetative and reproductive periods; (B) seedling stage. BrP, plants from brown seeds; BlP, plants from black seeds. Different letters above the bars indicate significant differences (P < 0·05) in the length of the life span or seedling stage, and different letters in the bars significant differences (P < 0·05) in the length of the vegetative or reproductive period. Upper case letters indicate differences across all germination dates in the same seed type, and lower case letters differences between seed types for the same germination date.

Fig. 2.

Effects of germination date and seed type on vegetative and reproductive characteristics of Suaeda corniculata. (A) Plant height; (B) root mass; (C) shoot mass; (D) root/shoot mass ratio; (E) vegetative mass; (F) total seed mass; (G) total seed mass/vegetative mass ratio. BrP, plants from brown seeds; BlP, plants from black seeds. Different upper case letters indicate significant differences (P < 0·05) across all germination dates in the same seed type, and different lower case letters significant differences between seed types for the same germination date.

Fig. 3.

Effects of germination date on the number of offspring seeds per plant (A, B) and seed diameter (C, D) of Suaeda corniculata for plants from brown seeds and plants from black seeds. ND, no data. Different upper case letters indicate significant differences (P < 0·05) across all germination dates for the same seed type, and different lower case letters significant differences between seed types for the same germination date and seed type.

Fig. 4.

Germination percentage of fresh dimorphic seeds of Suaeda corniculata under four temperature regimes. BrP, plants from brown seeds; BlP, plants from black seeds. Different upper case letters indicate significant differences (P < 0·05) across all temperature regimes for the same germination date, and different lower case letters significant differences across all germination dates at the same temperature.

Fig. 5.

Mean air temperatures (°C) and precipitation (mm) in the habitat of Suaeda corniculata from 1991 to 2009.