Symbiosis between land plants and microbes, such as rhizobia and mycorrhizal fungi, improves nutrient acquisition and plant fitness under nutrient limiting conditions. Sustainable agricultural practices leveraging plant-microbe symbiosis could enable reduced synthetic fertilizer application, reduce greenhouse gas emissions, and improve plant yield. A better understanding of the plant and microbial genetics contributing to differences in symbiosis and its effects on host fitness will help identify gene traits and microbial consortia that improve plant nutrient uptake and plant productivity. Common methods for assessing plant-microbe fitness, such as plant biomass weight, root nodule number and size, and root length colonization, are destructive and lack spatiotemporal information. A more ideal direct and in situ measurement of resource exchange between a plant and its symbionts would facilitate characterization of plant development in response to changes in nutrient demand and symbiont sink strength. In this presentation, I will highlight our multimodal 3D imaging pipeline that combines chemical tracer information from 11C positron emission tomography (PET) with root structure information from x-ray computed tomography (XCT) to measure changes in carbon allocation and root organ development in two different symbiotic systems. In our first study, we evaluated the effects of Bradyrhizobium on root growth and nodule development in soybean plants. Soybean plants grown with Bradyrhizobium exhibited an increase in 11C carbon allocation to root nodules resulting in slower root growth rate. In our second study, we characterized the effects of arbuscular mycorrhizal fungi (AMF) on belowground carbon allocation and root growth in maize plants. Plants grown with AMF invested more 11C belowground to support AM symbiosis and lateral root growth. Altogether, these studies highlight the effects of plant-microbe symbiosis in shifting plant nutrient foraging strategy and root system architecture as characterized by our in situ multimodal 3D imaging pipeline combining 11C PET and XCT technologies.
