Sticky Roots: Plants and microbes poised to attack mineral-associated organic matter

Gaps exist in our understanding of the mechanisms through which rhizodeposition by plant roots can mobilize mineral-associated organic matter (MAOM), exposing it to microbial attack. Yet the capacity of rhizodeposition to mobilize the large pool of MAOM could contribute to strong feedbacks among plant-microbial associations and soil carbon cycling. In a multi-institutional project, we are developing plant viral infection (aboveground) as a tool to alter rhizodeposition and probe effects of that alteration on MAOM mobilization and mineralization. Here, we infected Avena sativa (oat) with barley yellow dwarf virus (BYDV) in combined hydroponics and soil experiments. BYDV infects a broad range of natural and agricultural grasses and can lead to an overall increase in phloem flow, potentially spurring increased delivery of phloem contents to growing root tips and the rhizosphere, making them sticky. To assess plant and microbial responses to virus-induced shifts, we measured plant physiological properties, rhizodeposits composition (FTICR-MS), and microbial community structure (16S rRNA gene sequencing). In soil-grown plants, we found infection significantly decreased leaf-level photosynthesis, plant biomass, and root:shoot ratio. In hydroponic liquid, we detected increased carbohydrates and amino sugars around roots of infected vs. uninfected oats, supporting the idea that resources available to rhizosphere microbes may be altered by infection. The microbial community around roots in soil differed among treatments (acting as a biosensor), with e.g. Acidobacteria and Gemmatimonadetes more prominent around roots of infected vs. uninfected oats. These results indicate that virus-induced shifts in rhizodeposition may alter microbial community structure, with the potential to alter mobilization and mineralization of MAOM and influence soil carbon storage. Our next step is a greenhouse experiment combining plant infection, microbial metaomics analyses, and tracking of mobilization and mineralization of MAOM in soil using stable isotopic techniques.