Dissertation Research: Local adaptation and gene flow: The legume-rhizobia mutualism and edaphic heterogeneity

虽然细菌对较大生物体的负面影响是众所周知的，但更神秘的是它们对宿主可能产生的大量积极影响。一个典型的例子是豆科植物，如豆类和三叶草，从根瘤菌中获得的固氮细菌所带来的好处。植物将能量丰富的光合糖交换到根瘤中的细菌，以换取细菌获得的氮，这是植物生长的一种限制营养。这种共生已被证明是一种非常有效的策略，豆科植物可以在各种各样的栖息地持久存在。豆科植物在任何特定环境中的表现取决于植物和根瘤菌对场地特定方面的适应程度，因为两者高度相互依赖。然而，关于寄主植物与根瘤菌适应对配偶双方生存的相对重要性，人们知之甚少。这个项目解决了原生豆科植物和入侵豆科植物及其根瘤菌伙伴在蛇形露头和蛇形露头外的相互作用有何不同。这些露头蕴藏着加州本土植物多样性的残余物，受到恶劣土壤条件的保护，不受大多数入侵植物的侵袭。原生或入侵的豆科植物也许能够在没有特定根瘤菌的帮助下适应这种恶劣的环境，或者它们可能依赖于具有专用于该特定环境的共生体。了解蛇纹石土壤上和土壤外豆类根瘤菌共生的性质，是管理和保护这些受到威胁的植物群落的重要第一步。本科生将参与这项研究，结果将通过现有的网页公开。

While the negative effects of bacteria on larger organisms are familiar, more mysterious are the multitudes of positive effects they can have on their hosts. One model case is the benefit leguminous plants, like beans and clovers, receive from nitrogen-fixing bacteria called rhizobia that live in the plant's roots. Plants trade energy-rich photosynthetic sugars to bacteria housed in root nodules for bacterially-obtained nitrogen, a limiting nutrient for plant growth. This symbiosis has proven to be a highly effective strategy, and legumes can persist in a wide variety of habitats. The performance of a legume in any particular environment can depend on how well adapted both the plant and rhizobia are to the particular aspects of a site, since both partners are highly interdependent. However, very little is known about the relative importance of host plant versus rhizobia adaptations to the survival of either partner. This project addresses how interactions between a native and an invasive legume and their rhizobial partners differ on and off serpentine outcrops. These outcrops harbor remnant pockets of California's native floral diversity, protected from most invasive plants by harsh soil conditions. Native or invasive legumes may be able to adapt to this harsh environment without the aid of specific rhizobia, or they may depend on having symbionts that are specialized for that particular environment. Understanding the nature of legume-rhizobia symbioses on and off serpentine soils is an essential first step toward managing and conserving these threatened plant communities. Undergraduate students will be involved in this research, and results will be made public via an existing webpage.