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

种子萌发和幼苗生长是植物生命周期中最脆弱、压力最大的阶段。这在恶劣、不可预测和动态的栖息地尤其如此，因为只有短暂的有利条件才能成功地建立幼苗。提高发芽速度和幼苗生长是解决这一问题的可能办法，因为它可以降低幼苗死亡率。快速发芽的能力（即在一天或几天内）需要大量的种子生态和形态适应，例如不休眠和完全发育的胚胎。苋科/藜科（A/C）联盟包含大量快速发芽的物种。此外，在开花植物中萌发最快的是藜科植物，其胚胎呈螺旋状盘绕。有趣的是，a /C联盟中快速发芽的物种中有很高比例是C4植物和异精植物。本项目的目的是研究A/C复合体作为一个整体和Atriplex作为一个物种丰富、种子性状高度多样化的属的种子快速萌发的进化和适应性。我们将重建祖先性状状态来追踪种子性状的进化，并在分子系统发育的基础上寻找萌发速度、种子性状、营养植物性状和生境条件的相关进化。我们将测试的主要假设是：1。快速发芽是对有压力的生境条件的适应。2. 在逆境环境下的物种进化出了特定的种子形态特征，使其能够快速发芽。3. 短寿命物种和先锋物种比长寿命物种从快速发芽中获益更多。4. 在种子二态性、种子质量、种子休眠和种子传播等下注对冲机制之间存在权衡。5. 较高的萌发速度与C4光合作用共同进化，C4光合作用使幼苗生长和建立更快。

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.