Effect of Temperatures on Dormancy and Germination in Three Species in the Lamiaceae Occurring in Northern Wetlands

Abstract

In the temperate region temperature is the main factor influencing the germination period of plant species. The purpose of this study was to examine effects of constant and fluctuating temperatures on dormancy and germination under laboratory and field conditions in the three wetland species Lycopus europaeus, Mentha aquatica and Stachys palustris. The results should give indications if the temperature-dependent regulation of dormancy and germination is phylogenetically constrained. Tests for germination requirements showed a minimum temperature for germination of 9°C in Mentha and 12°C in Lycopus and Stachys, and a maximum temperature of 33°C for Lycopus and 36°C for Mentha and Stachys. Fluctuating temperatures promoted germination in all three species but the amplitude required for high germination (>50%) differed: it was 8°C in Mentha, 10°C in Stachys and 14°C in Lycopus (mean temperature 22°C). The effect of temperatures on the level of dormancy was examined in the laboratory by imbibing seeds at temperatures between 3°C and 18°C for periods between 2 and 28 weeks, as well as by a 30-month burial period, followed by germination tests at various temperatures, in light and darkness. In the laboratory only low temperatures ( £ 12°C) relieved primary dormancy in seeds of Lycopus, while in Mentha and Stachys also higher temperatures lead to an increase of germination. Dormancy was only induced in Lycopus seeds after prolonged imbibition at 12°C in the laboratory. Buried seeds of all species exhibited annual dormancy cycles with lower germination in summer and higher germination from autumn to spring. Exhumed seeds, however, showed considerable differences in periods of germination success. Dormancy was relieved when ambient temperatures were below 12°C. Ambient temperatures that caused an induction of dormancy varied depending on species and test condition, but even low temperatures (8°C) were effective. At high test temperatures (25°C) in light, exhumed seeds of all three species showed high germination throughout the year. The three species showed various differences in the effects of temperatures on dormancy and germination. Similarities in dormancy and germination found among the species are in common with other spring-germinating species occurring in wetlands, so it seems that the temperature dependent regulation of dormancy and germination are related to habitat and not to phylogenetic relatedness.

Dormancy and germination in Stachys germanica L. subsp. bithynica (Boiss.) Bhattacharjee seeds: Effects of short-time moist chilling and plant growth regulators

“…The dormant status of the seeds is probably not related to the seed coat. Similar results were found by Brändel (2006) for Stachys palustris.…”

Restoration guidelines for wetlands of the western Prairie Pothole Region /

“…Timing of seeding requires considering the optimum temperature range required for germination. Although there can be slight differences in germination temperature requirements among similar species (Brandel 2006), most northern temperate wetland species germinate to higher percentages under fluctuating day/night temperatures, generally with at least a 10 to 15º F diurnal temperature difference.…”

Seed Germination and Early Growth Responses of Hyssop, Sweet Basil and Oregano to Temperature Levels

“…For three species, the highest germination rate occurred in moderate and warm temperatures like germination percentage, indicating that these temperatures may be optimum range of temperatures for their germination. Brändel (2006) reported that the minimum temperature for germination of Mentha aquatica was 9 °C and 12 °C in Lycopus europaeus and Stachys palustris (three species from lamiaceae family), and a maximum temperature of 33 °C for L. europaeus and 36 °C for M. aquatica and S. palustris. For majority of plant species, optimum and ceiling temperatures have been reported from ranges of 15-30 °C and 30-40 °C, respectively (Copeland and McDonald, 1995).…”