• Mediterranean back dune species
• seed germination
• global warming
• fresh
• after-ripening
• thermal limits

Annual plant species in Mediterranean coastal dunes are subject to extreme environmental conditions, including high soil temperature and water stress, which threaten their survival. As annual plant species must regenerate each year by seeds, they are particularly affected by environmental cues due to climate change, reducing water availability during certain periods and increasing temperature during the whole year. Additionally, the disruption of the natural seed dormancy cycles is an important problem that occurs with the climate change. This leads an advanced or delayed seed germination and following seedling emergences under unfavorable periods. This study is designed to assess the hypothesis that, Mediterranean back dune species may germinate at cool temperatures and be not pre-adapted to global warming or may germinate at higher temperature and be pre-adapted to global warming. If these species germinate at the cooler temperatures during autumn/winter period, their germination is finely tuned to the current climate, avoiding of high risk seedling mortality in summer season. Alternatively, these species may also exhibit pre-adaption to global warming, characterized by a broad germination thermal niche breadth.

Therefore, this study aims to understand how seeds respond to environmental cues, simulating current and future climatic conditions in laboratory. We sampled three characteristic annual species in the back dunes of the central Mediterranean: Festuca fasciculata Forssk. (Poaceae), Marcus-kochia ramosissima (Desf.) Al-Shehbaz and Silene canescens Ten. (Caryophyllaceae). Seeds were collected in late spring from approximately 100 randomly selected individuals for each species. They were immediately sown on plain agar to quantify the dormancy level at dispersal (fresh seeds) or after-ripened (~20°C, 50% RH; ~25°C, 20% RH; ~35°C, 15% RH) for 6 months. Seeds were exposed to different temperatures (5, 10, 15, 20, 25 and 35), 2 temperature regimes (constant and alternating) and 2 light conditions (diurnal light and constant dark) for a total of 32 experimental treatments.

We found that fresh seeds reach very low germination proportions (3-4%) at any condition in all species, while after-ripening overcomes dormancy, allowing for wide germination responses. Germination temperature optimum was around 20°C for Festuca fasciculata and 25°C for Silene canescens, which is higher compared to the majority of Mediterranean species, while Marcus-kochia ramosissima seeds germinate at low percentage, thus this species probably exhibits deeper dormancy.Studying seed responses to current and future climatic scenarios, will allow to identify the thermal germination thresholds, as critical information to forecast the germination risk and to define future potential threats to the long-term persistence of back dune species in Mediterranean habitat, avoiding biodiversity losses.