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.
