Conditional cold avoidance drives between-population variation in germination behaviour in Calluna vulgaris

Area of Science:

• Ecology
• Plant Biology
• Evolutionary Biology

Background:

• Widely distributed species exhibit life history variations due to diverse environmental conditions.
• Seed germination in cold climates can involve cold tolerance or cold avoidance strategies.
• Calluna vulgaris, a dominant heathland species, displays contrasting germination responses to winter temperature variations.

Purpose of the Study:

• To investigate the germination responses of Calluna vulgaris populations across bioclimatic gradients.
• To determine if germination strategies vary with latitude and altitude in Norway.
• To understand the adaptive significance of germination timing in different climatic conditions.

Main Methods:

• Collected Calluna vulgaris seeds from ten populations across Norwegian latitude and altitude gradients.
• Assessed germination rates and percentages under controlled incubation temperatures (10–25 °C).
• Analyzed germination performance in relation to seed collection site's temperature conditions and seed mass.

Main Results:

• All populations exhibited high germination at warmer temperatures (25 °C).
• Populations from colder climates showed significantly lower germination rates and percentages at low temperatures (10 °C).
• Seed mass influenced germination but did not explain the observed variation along climatic gradients.

Conclusions:

• Calluna vulgaris populations display a cold-avoidance germination strategy, with higher temperature requirements in colder climates.
• This strategy suggests a shift in selection pressures from climatic adversity to competitive performance.
• Germination timing is a crucial adaptive trait for exploiting the growing season effectively in varying climates.