Evolution of dispersal and pollination in ecologically dominant grasses

北美的高草草原是美国历史上的标志性景观。草原得名的那些草与构成东非广阔草原的那些草是近亲。这些草为牲畜和野生动物提供食物，也为鸟类提供栖息地；它们还从大气中吸收碳并将其深埋在地下，在那里它支持有益的微生物，这些微生物形成了美国农业所依赖的肥沃土壤。这个项目是密苏里州圣路易斯市唐纳德·丹福斯植物科学中心的研究科学家、伊利诺伊州埃尔萨市普林西亚学院的本科生和东非的同事们合作完成的，旨在揭示草传播花粉的方式，它们如何为种子提供碳，以及种子如何在景观中传播。这些信息将告诉我们，面对当前的干扰，如火灾、城市化和农田改造，以及气候变化引起的未来干扰，草原将如何应对。该项目重点研究了三个主要的草属，Andropogon， Schizachyrium和Hyparrhenia，以及一些较小的相关属，总共包括大约250个物种，其中许多是生态优势。研究人员将首先使用DNA序列来揭示这一群体的系统发育历史，然后利用这一历史来追踪植物的种子部分在进化过程中是如何变化的，以及它们与气候、火灾和湿度的关系。这些植物的种子不是简单地从植物上掉下来的。相反，它们是作为一个复杂的扩散结构的一部分释放出来的，这个结构包括花茎和叶状苞片。不同物种的分布结构在大小、有无毛、有无雄花和雌花、有无芒（苞片的吸湿延伸）等方面各不相同。这种结构可能是为了适应种子的传播，在特定的土壤类型中控制发芽，或者是为了耐火。然而，同样的结构也可能有助于授粉。此外，扩散结构的许多部分在发育过程中是绿色的，可能为发育中的种子提供光合物质。因此，该结构可以在传粉、灌浆和传播三个不同的生活史阶段发挥作用。该项目将使用历史系统发育方法和实验方法来测试分散结构的当前功能。这里研究的分布结构与高粱、甘蔗和芒草的分布结构非常相似，因此这些数据将适用于这些作物以及主要的草原物种。

The tallgrass prairie of North America is an iconic landscape, central to America history. The grasses from which the prairie takes its name are close relatives of those that make up the vast grasslands of eastern Africa. The grasses provide food for livestock and wild animals, and habitat for birds; they also pull carbon from the atmosphere and bury it deep in the ground where it supports beneficial microbes that make the rich soil on which American agriculture depends. This project is a collaboration between research scientists at the Donald Danforth Plant Science Center in St. Louis, Missouri, undergraduates at Principia College in Elsah, Illinois, and colleagues in eastern Africa, and is aimed at unraveling the ways the grasses spread their pollen, how they provide their seeds with carbon, and how the seeds are dispersed across the landscape. This information will tell us how the grasslands will respond in the face of current disturbance such as fire, urbanization, and conversion to farmland, and future disturbances caused by a changing climate. This project focuses on three major grass genera, Andropogon, Schizachyrium, and Hyparrhenia, plus a few smaller related genera, that together include some 250 species many of which are ecological dominants. Researchers will first use DNA sequences to uncover the phylogenetic history of the group, and then use that history to trace how the seed-bearing portions of the plant have changed over evolutionary time and how they correlate with climate, fire, and moisture. The seeds in these plants do not simply drop off the plant. Instead they are released as part of a complex dispersal structure that includes pieces of floral stalks and leaf-like bracts. The dispersal structure varies between species in size, presence or absence of hairs, presence of male and female flowers, and presence or absence of awns (hygroscopic extensions of bracts). The structure may be an adaptation for seed dispersal, for the control of germination in particular soil types, or for resistance to fire. However, the same structures may also help with pollination. In addition, many parts of the dispersal structure are green during development, and may provide photosynthate for the developing seed. Thus the structure could be selected for functions at three different life history stages: pollination, grain filling, and dispersal. This project will use both a historical phylogenetic approach and an experimental approach to test the current function of the dispersal structure. The dispersal structure studied here is much like that of sorghum, sugarcane and Miscanthus, so the data will apply to those crops as well as to the major grassland species.