This week’s BEACON Researchers at Work blog post is by MSU graduate student Tomomi Suwa.
Tomomi inoculating hog peanuts with rhizobia
When you get thirsty, what do you do? You simply get something to drink, right? Plants don’t have the ability to move like animals, so they had to come up with other strategies to deal with stress like drought, heat stress, and salinity. For example, they can reproduce and disperse seeds to less stressful habitats or they can associate with other organisms, such as symbiotic microbes, that can “help them out” when times get tough. Although the second strategy has received very little attention, there is increasing evidence that interacting species, particularly microbial symbionts, are capable of facilitating plant adaptation to stress.
Ecologically, there is lots of evidence supporting that microbial symbionts can facilitate a plant’s tolerance to abiotic stress. For example, resource mutualists, such as arbuscular mycorrhizal fungi and nitrogen-fixing bacteria, can help plants acquire nutrients and can help mitigate the effects of drought and low pH. Evolutionarily, genetic variation in microbial symbionts may even facilitate plant adaptation to local environments. Given their short generation times, genetic diversity and dispersal ability, rapid evolution of microbial symbionts may facilitate adaptive plant responses to environmental stress.
Can you find nodules in the roots?
My research focuses on whether soil bacteria make it possible for plants to adapt to and live in different habitats. One type of soil bacteria, called rhizobia, infect the roots of plants from the Fabaceae family (a.k.a legumes). Once inside the root, they form “root bumps,” called nodules. Rhizobia live inside the root nodules and convert nitrogen in the atmosphere into ammonia, in a form that legumes can use (like a natural fertilizer!). In turn, legumes provide photosynthetic carbon to the rhizobia. Rhizobia therefore can help plants grow in areas where they might not live otherwise. But just like human relationships, plants and rhizobia may not be compatible, or one of the partners may not be even available! For example, rhizobia may not survive or convert nitrogen effectively in certain environmental conditions, like dry soil or shade. Using a native legume called the hog peanut (Amphicarpaea bracteata), I study how mutualism between plants and rhizobia are affected by environmental stress.
In particular, I test whether rhizobia mediate plant adaptation to soil moisture, a well-characterized stressor to plants that also is known to influence plant-microbe interactions. I’m interested in three specific questions: 1) Are plants locally adapted to soil moisture conditions? 2) Do resource mutualists contribute to plant adaptation to soil moisture? 3) What plant traits drive adaptation to wet vs. dry environments?
Reciprocal transplant experiment in progress
I am currently conducting a series of field and greenhouse experiments to test these questions. I don’t have all the answers yet, but so far I have found soil moisture affects nodulation and benefits that rhizobia provide to plants. I also found that there’s genetic variation for symbiosis-related traits (e.g. nodulation, nodule size) among plant genotypes, suggesting the potential for plants and rhizobia to co-evolve in response to soil moisture. My goal of this project is to expand our understanding of the mechanisms behind local adaptation in two ways. First, I will examine whether symbiotic mutualists are contributing to local adaptation to soil moisture. Given the intimate relationships between plants and symbiotic microbes, it is likely that rhizobia play a role in plant adaptation. Second, I will identify environmental factors driving local adaptation and phenotypic traits under selection, which are critically important to understanding the cause of natural selection and variation in selection among local habitats.
High school students from KAMSC conducting an experiment testing the effects of fertilization on soybean-rhizobia interactions
Sam Peters (high school student from KAMSC) working on his independent project in winter 2013
Plant-rhizobia as educational tool: Along with a research on plant-rhizobia interactions, I have shared my excitement for this topic with middle school and high school students. For example, through a BEACON education project, I had an opportunity to mentor a motivated high school student from Kalamazoo Math and Science Center on his independent project, testing whether rhizobia from different soil nitrogen have evolved differently to benefit the plants. I also worked with Brad Williamson, a former president of National Biology Teachers, to create a guided inquiry biology lesson, using the plant-rhizobia symbiosis as a model system (in review for The American Biology Teacher). In this lesson, students gain experience in scientific methods by coming up with hypothesis, designing and conducting experiments, to making claims based on the data they collect. We think that the plant-rhizobia interaction is an excellent system to teach inquiry-based science at high school and college levels.
For more information about Tomomi’s work, checkout her website at tomomisuwa.com or contact suwatomo at msu dot edu.
