Symbionts and saprotrophs: Cooperation and competition in the rhizosphere determine belowground feedbacks

A major goal of ecosystem science is to understand complex processes occurring belowground. These hidden processes involve microbial communities made up of bacteria and fungi. It has been difficult to correctly identify and measure the mechanisms operating belowground. Specifically, the balance between saprotrophs (organisms that feed on decaying organic matter) and mycrorrhizae (fungi that have a symbiotic relationship with the roots of many plants) has been difficult to understand. It is commonly assumed that saprotrophs are pretty much all alike with respect to their traits and function. However, some recent data demonstrate that saprotrophic community composition, and interactions between mycorrhiza and saprotrophs, have a significant impact on ecosystem carbon cycling. This project advances our fundamental understanding of the belowground interactions that regulate ecosystem function. The project conducts experiments in a forest in West Virginia to develop, parameterize, and validate representations of these interactions in an ecosystem model. The project also provides hands-on learning activities for K-12 students, undergraduate biology students, graduate students, and postdoctoral scholars. The goal of the project is to determine how cooperative and competitive soil microbial interactions shape ecosystem level carbon and nitrogen cycling. This knowledge is used to improve the sophistication and performance of an ecosystem model. The Carbon Acquisition Ecological Strategies (CAES) framework has been developed to facilitate the incorporation of soil saprotrophic microorganisms into a leading model of below ground ecosystem function (the Carbon, Organisms, Rhizosphere, and Protection in the Soil Environment (CORPSE) model). In CAES, soil saprotrophs are classified into groups that are similar to the carbon pools in CORPSE. This project provides the empirical data necessary for parameterization of this model. The project uses a field experiment, a greenhouse experiment, and different techniques like quantitative stable isotope probing to identify the taxonomic composition of saprotrophic functional groups in different soil environments. Ultimately, the research links cross-scale experiments with a novel modeling platform (CAES-CORPSE) to transform our predictive understanding of belowground processes. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.