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

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

Could plant diversity metrics explain climate-driven vegetation changes on mountain summits of the GLORIA network?

High-elevation habitats host a large number of plant species and are characterized by high biodiversity. The vegetation 31 dynamics in these cold adapted ecosystems are difficult to predict, being affected by global warming, especially in the 32 last decades. With the aim to promote a better understanding of climate-driven changes of alpine vegetation, we 33 investigated the variation in species richness, α-diversity, β-diversity, and total cover of plant functional types over a 34 time lapse of 15 years, relying on multiple re-surveys of mountain summit vegetation in 2001, 2008 and 2015. The 35 study area, included in the long term global observation network GLORIA, was at the boundary between temperate and 36 mediterranean mountains of S-Europe (northern Apennines, Italy). We identified a trend of loss in biodiversity and 37 signals of biotic homogenization using multiple diversity metrics, despite the overall species richness increment 38 observed in the study area. Cold-adapted and rare species declined while dominant species like shrubs and graminoids 39 increased. Our results highlights that long-term vegetation monitoring activities paired with multiple measures of 40 diversity are required to properly assess biodiversity and to obtain useful indications for future conservation activities in 41 alpine environments. The methods here presented could be applied in all GLORIA sites to quantify biodiversity changes 42 over time, obtaining comparable results for biodiversity monitoring in high-elevation habitats from all over the world

List of species used in the experiment.

<p>Information on species chorotype was adapted from Alessandrini <i>et al</i>. 2003 [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0133626#pone.0133626.ref042" target="_blank">42</a>]. For each species we reported the site and the elevation of the collected population.</p><p>Nomenclature follows Conti <i>et al</i>. 2005 [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0133626#pone.0133626.ref064" target="_blank">64</a>] and Peruzzi <i>et al</i>. 2010 [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0133626#pone.0133626.ref065" target="_blank">65</a>] and successive updates.</p

Autumn germination percentage (means ± s.e.) of ten species at different water potentials (MPa) under BASE treatment (B) and autumn heat waves (HW1).

<p>Autumn germination percentage (means ± s.e.) of ten species at different water potentials (MPa) under BASE treatment (B) and autumn heat waves (HW1).</p

Temperatures during the different days of the incubation treatments and the equivalent week (w.) of the year.

<p>The two HW treatments are highlighted in bold.</p

Cumulative germination percentage (means ± s.e.) of each species (<i>Hypericum</i>-<i>Vaccinium myr</i>) under three temperature treatments at the end of autumn (black columns) and at the end of summer (white columns).

<p>Winter germination is not shown since no seeds germinate during cold stratification period. Final germination is given by the sum of black and white. Lowercase letters indicate significant differences of germination at P<0.05 level (Tukey's honest significance test) in autumn. Capital letters indicate significant differences of final germination at P<0.05 level (Tukey's honest significance test) (i.e. sum of autumn and spring/summer germination).</p

Results of the generalized linear mixed effects models (GLMMs) on the effects of treatments (HW1, HW2 and B) on autumn, summer and final seed germination.

<p>Results of the generalized linear mixed effects models (GLMMs) on the effects of treatments (HW1, HW2 and B) on autumn, summer and final seed germination.</p