Climate warming could shift the timing of seed germination in alpine plants

Abstract

Background and aims: Despite the considerable number of studies on the impacts of climate change on alpine plants, there have been few attempts to investigate its effect on regeneration. Recruitment from seeds is a key event in the life-history of plants, affecting their spread and evolution and seasonal changes in climate will inevitably affect recruitment success. Here, an investigation was made of how climate change will affect the timing and the level of germination in eight alpine species of the glacier foreland.

Methods: Using a novel approach which considered the altitudinal variation of temperature as a surrogate for future climate scenarios, seeds were exposed to 12 different cycles of simulated seasonal temperatures in the laboratory, derived from measurements at the soil surface at the study site.

Key results: Under present climatic conditions, germination occurred in spring, in all but one species, after seeds had experienced autumn and winter seasons. However, autumn warming resulted in a significant increase in germination in all but two species. In contrast, seed germination was less sensitive to changes in spring and/or winter temperatures, which affected only three species.

Conclusions: Climate warming will lead to a shift from spring to autumn emergence but the extent of this change across species will be driven by seed dormancy status. Ungerminated seeds at the end of autumn will be exposed to shorter winter seasons and lower spring temperatures in a future, warmer climate, but these changes will only have a minor impact on germination. The extent to which climate change will be detrimental to regeneration from seed is less likely to be due to a significant negative effect on germination per se, but rather to seedling emergence in seasons that the species are not adapted to experience. Emergence in autumn could have major implications for species currently adapted to emerge in spring.

Fig. 1.

Mean daily temperatures (°C) about 2 cm deeep in the soil at the species growing site (2500 m a.s.l., dashed line) and at 400 m lower (2100 m a.s.l., continuous line), between September 2009 and September 2010.

Fig. 2.

Cumulative germination percentage (means ± s.e.) of each species under three temperature treatments at the end of autumn (September, black columns) and at the end of spring/summer (August, white columns). See Table 1 for the incubation temperatures. Winter germination has been omitted because no seeds germinated during incubation at this temperature. Different letters indicate significant differences of germination at P < 0·05 level (Tukey multiple comparison test).

Fig. 3.

Percentage germination (means ± s.e.) of each species at the end of the three temperature treatments listed in Table 1, performed in the absence of an autumn simulation. Also shown are the same results after subzero winter temperature (–7 °C, dashed columns), but only if significantly different from the winter-treated seeds performed at 0 °C. Winter germination has been omitted because no seeds had germinated during incubation at this temperature. Different letters indicate significant differences of germination at P < 0·05 level (Tukey multiple comparison test).

Fig. 4.

Mean time to germinate of each species under three autumn temperatures. See Table 1 for the incubation temperatures. Different letters indicate significant differences of MTG at P < 0·05 level (Tukey multiple comparison test).

Fig. 5.

Mean time to germinate in spring/summer for each species and temperature treatment listed in Table 1 performed in the absence of autumn. Also shown are the same results after subzero winter temperature (–7 °C, dashed columns), but only if significantly different from the winter-treated seeds performed at 0 °C. Different letters indicate significant differences of MTG at P < 0·05 level (Tukey multiple comparison test).