Mesoclimatic origin affects alpine plant germination but not its plasticity

Abstract

Mountain ecosystems are disproportionately exposed to global warming, which may put alpine plant species in particular at risk. Plant species' migration and persistence depend on successful seed regeneration, with demographic traits such as germination being strongly sensitive to both present and ancestral climate. Germination may, thus, present a major bottleneck to alpine plant species under climate change, or they may cope through phenotypic plasticity. However, little is known about alpine plant germination under warming, its plasticity, and whether any of these are co‐determined by the climatic origin of the seeds. We investigated intraspecific variation in germination proportion and timing of six co‐occurring alpine plant species from different micro‐ and mesoclimatic origins as response to three temperature treatments using growth chambers. Elevation as well as topographic strata were used as proxies for mesoclimate and mean soil temperature, growing‐ as well as freezing‐degree‐days for microclimate. Our results show that species were plastic in germination proportion and timing in response to temperature, with all species germinating in the warmest treatment. Micro‐ and mesoclimatic origin affected germination traits but did not co‐determine species responses to the temperature treatments. We also demonstrated maternal climatic effects, with seeds from warmer microclimates displaying higher phenotypic plasticity. Furthermore, seeds originating from colder mesoclimates, i.e. the upper elevation range, generally germinated less. Our results suggest that global warming will impact alpine plant regeneration from seeds through concurrent effects during germination, climatic origin as well as shifts in germination timing. Importantly, our results indicate that regeneration from seed may contribute to defining the upper elevational limit of alpine plant species through climatic origin and maternal microclimatic effects.