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.
Highlights
Climate warming is one of the main drivers of future ecosystem changes [1]
In the absence of heat waves, seed germination mainly occurred in spring, after seeds had experienced autumn and winter seasons
The present study investigated the effects of short-term heat events on the germination of alpine plants by exposing the seeds of 53 high mountain species that grow in the Northern Apennines (Italy) to different temperature treatments and water potentials in the lab, simulating heat waves that occurred in southern Europe in spring 2003 and autumn 2011
Summary
Climate warming is one of the main drivers of future ecosystem changes [1]. Current knowledge about plant response to climate change is largely based on the effects of climatic trends, such as gradual warming. Over the last twenty years, extreme weather events, such as heat waves, drought, late frost events and heavy and irregular rainfalls have increased in frequency and intensity [2,3,4,5], bringing about changes to ecosystems [6,7]. In this regard, heat waves (defined by the WMO World Meteorological Organization as a period in which the daily maximum temperature of more than five consecutive days exceeds the average maximum temperature by 5°C, the normal period being 1961–1990) are one of the most studied phenomena [8,9], having shown a significant increase in frequency and duration in the northern hemisphere [10,11,12]. Heat waves may favour plant performance (in the absence of drought), by increasing photosynthetic activity [28] and overall plant fitness through acclimation to warmer conditions [29]
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