Effects of Autumn and Spring Heat Waves on Seed Germination of High Mountain Plants

Abstract

Alpine plants are considered to be particularly vulnerable to climate change and related extreme episodes, such as heat waves. Despite growing interest in the impact of heat waves on alpine plants, knowledge about their effects on regeneration is still fragmentary. Recruitment from seeds will be crucial for the successful migration and survival of these species and will play a key role in their future adaptation to climate change. In this study, we assessed the impacts of heat waves on the seed germination of 53 high mountain plants from the Northern Apennines (Italy). The seeds were exposed to laboratory simulations of three seasonal temperature treatments, derived from real data recorded at a meteorological station near the species growing site, which included two heat wave episodes that occurred both in spring 2003 and in autumn 2011. Moreover, to consider the effect of increasing drought conditions related to heat waves, seed germination was also investigated under four different water potentials. In the absence of heat waves, seed germination mainly occurred in spring, after seeds had experienced autumn and winter seasons. However, heat waves resulted in a significant increase of spring germination in c. 30% of the species and elicited autumn germination in 50%. When heat waves were coupled with drought, seed germination decreased in all species, but did not stop completely. Our results suggest that in the future, heat waves will affect the germination phenology of alpine plants, especially conditionally dormant and strictly cold-adapted chorotypes, by shifting the emergence time from spring to autumn and by increasing the proportion of emerged seedlings. The detrimental effects of heat waves on recruitment success is less likely to be due to the inhibition of seed germination per se, but rather due to seedling survival in seasons, and temperature and water conditions that they are not used to experiencing. Changes in the proportion and timing of emergence suggest that there may be major implications for future plant population size and structure.

Germination responses to winter warm spells and warming vary widely among woody plants in a temperate forest

“…If autumn habitat temperatures rise high enough so that they overlap with the germination envelope of fresh seeds, seedling emergence could be triggered in the field. Indeed, alpine plants have been shown to have the potential to shift to autumn (from spring) germination with autumn heatwaves (Orsenigo et al 2015). Such a shift does not need to be limited to alpine regions, since populations of species in temperate regions have also been shown to have potential to shift (Bandara et al 2019).…”

Habitat‐related seed germination traits in alpine habitats

“…Examples of direct environmental features driving variation in germination strategies include habitat disturbance (Angevine & Chabot, ), altitude (Fernández‐Pascual, Jiménez‐Alfaro, & Bueno, ), soil nutrients (Hilhorst & Karssen, ), density of plant cover (Jankowska‐Blaszczuk & Daws, ), and chorology (Orsenigo et al., ). Despite the strong environmental control on plant regenerative traits (e.g., dispersal vectors, seed longevity, germination), they still remain underrepresented when studying the drivers of vegetation patterns in local and global scales (Kleyer et al., ).…”

Plant–environment interactions through a functional traits perspective: a review of Italian studies

“…Alpine plant seeds directly exposed to warming after dispersal showed a general increase in germination rate both in spring and autumn, with a subsequent high percentage of seedling survival in winter (Mondoni et al 2012(Mondoni et al , 2015Orsenigo et al 2015). The exposition of seeds of two Mediterranean annual species to water stress led to reduced and delayed germination with contrasting responses among populations, revealing a possible adaptation to drought stress in the southernmost population (Orsenigo et al 2017).…”