BIOGEOCHEMISTRY AMONGST NON-LEGUMINOUS PLANTS, ARBUSCULAR MYCORRHIZAL FUNGI, AND FREE-LIVING NITROGEN FIXERS IN TRIPARTITE ASSOCIATIONS
Creators: name: Kasanke, Shawnee Amelia
Publisher: name: Washington State University
Year: 2024
Subjects: subject: AM fungi
subject: Mutualism
subject: N-fixation
subject: Soil health
subject: Switchgrass
subject: Biogeochemistry
subject: Ecology
subject: FOS: Biological sciences

description: Microbial food webs are important drivers of global nutrient cycling and soil function. Interactions between microorganisms and their environments can quickly change in response to environmental shifts and disturbances. These disturbances can alter nutrient cycles and have subsequent impacts on soil health, water quality, greenhouse gas emissions, and other important ecosystem processes. Nutrient-exchange-based biological relationships can be leveraged to manage microbial driven ecosystem processes when controls on nutrient cycling are known. One successful application for utilizing biological nutrient exchange relationships is in sustainable agriculture, where interactions between plants and root associated microorganisms can reduce the need for inputs of synthetic fertilizer and improve overall soil health. Currently, the successful use of this approach is limited to a few specific cropping systems and environmental conditions. One common but variable plant-microbe relationship with potential for improving soil health exists between non-leguminous plants, free-living nitrogen-fixing bacteria (FLNF), and arbuscular mycorrhizal (AM) fungi. However, underlying controls on and mechanisms of resource exchange between these organisms remain poorly understood. To expand our understanding of potential benefits of tripartite associations between non-leguminous plants, FLNF, and AM fungi to plant and microbial health, this dissertation describes three studies that: 1) define the current state of knowledge regarding multipartite relationships between these key organisms, 2) expand our understanding of influential factors effecting microorganisms and plant responses to co-inoculation, and 3) describes a novel method to measure carbon (C) partitioning by taxonomically distinct groups of microorganisms. In the first study I showed that most research to date on tripartite relationships between non-leguminous plants and microorganisms are conducted under greenhouse growing conditions. Studies commonly use only 1-2 representative taxa of both FLNF and AM fungi as experimental inoculates and are generally focused on production outcomes of annual cereal crops. I also identified critical knowledge gaps where conditions that foster positive outcomes of co-inoculation are uncommonly tested. To address some of these knowledge gaps, in the second study, I demonstrated how plant phenology can be a powerful driver of both microbial community structure and functional gene abundance in root-affected soils, and, in the third study I described a new method to quantify C partitioning in fungi and bacteria. Collectively, this body of work is useful to inform new approaches to improve and manage soil health, direct future studies to fill important knowledge gaps, and provides a tool to improve assessment of C budgets across ecosystem types.