About This Project

Soils are not homogeneous ecosystems. While humans often focus on visible, above-ground life, beneath the surface exists remarkable microbial diversity with access to plant roots, mediating above-ground plant biodiversity. Point Reyes, a spatially heterogeneous coastal California ecosystem, is ideal for studying how soil microbial communities affect plant biodiversity. Thus, we will identify and compare the microbial communities of twenty plant species in Point Reyes.

Ask the Scientists

What is the context of this research?

Plant-associated microbes have specific ecological roles as mutualists and pathogens. Mutualists provide nutrients in exchange for carbohydrates, benefiting their plant hosts, while pathogens cause disease by disrupting physical barriers, manipulating host cell activities, and suppressing immune responses. However, plants associate with specific microbial guilds, like ectomycorrhizal (EM) or arbuscular mycorrhizal fungi (AM) and N-fixing bacteria, that differentially enhance plant resistance to pathogens. These interactions can generate positive or negative plant-soil feedback, where plants influence soil properties and vice versa, and are hypothesized to be key regulators of plant biodiversity, by suppressing or promoting plant species coexistence, respectively. However, the influence of mutualistic microbial guilds on the direction and strength of plant-soil feedback under plant competition is not well understood and requires further investigation.

What is the significance of this project?

To test how plant competition influences microbes to generate positive or negative plant-soil feedback, we must first characterize the mutualist-to-pathogen ratio in roots and soils of differing guilds where plant monodominance and biodiversity co-occur. Point Reyes, a coastal ecosystem, is ideal due to its patches of plant monodominance within a heterogeneous landscape hosting over 900 plant species (15% of California's flora). Here, EM-plants like bishop pines recruit microbes that act as a biological filter against competitors, reducing biodiversity. In contrast, AM-plants like coyote bush enhance soil conditions, promoting coexistence. Such work is crucial for conservation efforts by monitoring pathogen occurrence, determining coexistence outcomes, and predicting shifts in ecosystem functions. Given the rise of soil-borne pathogens and climate-induced niche shifts, it is vital to understand how mutualists generate below-ground feedbacks that mediate aboveground biodiversity.

What are the goals of the project?

The primary goal of this project is to characterize via DNA sequencing the identity and similarity of plant root and soil microbes within the same microbial guild then quantify the proportion of mutualists to pathogens in those samples. Such data will provide the foundation for a greenhouse study to test how competition between varying microbial guilds influences plant-soil feedbacks and above-ground biodiversity. 180 root and soil samples that differ in mutualistic microbial guild from twenty of the most prevalent plant species at Point Reyes will be collected in the Fall of 2025 and Spring of 2026. Further, this work will inform conservation efforts by enhancing our understanding of how microbes contribute to plant disease and inform us of the potential use of microbes for soil transfer to allow plant species to escape severe pathogen pressure or exhibit greater climate tolerance.