Evolution and ecology of fast seed germination in the Chenopodiaceae/Amaranthaceae alliance

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Seed germination and seedling growth are the most vulnerable and stressful phases in a plants life-cycle. This is especially the case in harsh, unpredictable and dynamic habitats where only short spells of favorable conditions allow for successful seedling establishment. Increasing germination speed and seedling growth is a possible solution to this problem because it reduces seedling mortality. The ability to germinate fast (i.e. within one or a few days) requires a number of seed ecological and morphological adaptations, e.g. non-dormancy and a completely developed embryo. The Amaranthaceae/Chenopodiaceae (A/C) alliance contains a high number of fast germinating species. Furthermore the fastest germinators in flowering plants have been recorded from Chenopodiaceae with spirally-coiled embryos. Interestingly a high proportion of fast germinating species in the A/C alliance are C4 plants and heterospermic. The goal of this project is to investigate the evolution and adaptive nature of fast seed germination in the A/C complex as a whole and in Atriplex as a species-rich genus with highly diverse seed traits. We will reconstruct ancestral characters states to trace the evolution of seed traits and we will search for correlated evolution of germination speed, seed characters, vegetative plant traits and habitat conditions on the basis of molecular phylogenies. The major hypotheses we will test are: 1. Fast germination is an adaptation to stressful habitat conditions. 2. Species in stressful habitats have evolved specific seed morphological traits enabling fast germination. 3. Short-lived species and pioneer species benefit more from fast germination than long-lived species. 4. Trade-offs exist between bet-hedging mechanisms such as seed dimorphism, seed mass, seed dormancy and seed dispersal. 5. Higher germination speed co-evolved with C4 photosynthesis and the latter enables for faster seedling growth and establishment.